Cross references:   Protobionts     Montmorillonite  
Last Universal (Common) Ancestor    Prokaryote Colonies   

Evolutionary History of Life (Wiki)    
Earth formed about 4.5 Ga (billion years) ago and there is evidence that life appeared within 0.5 billion years.[1] The similarities between all present-day organisms indicate the presence of a common ancestor from which all known species have diverged through the process of evolution.[2]
    "Microbial mats of coexisting bacteria and archaea were the dominant form of life in the early Archean and many of the major steps in early evolution are thought to have taken place within them "  


Archean Eon (Wiki) 
3.8 Ga (billion years) ago to 2.5 Ga. 
Fossils of cyanobacterial mats (stromatolites) are found throughout the Archean, becoming especially common late in the eon, while a few probable bacterial fossils are known from chert beds.In addition to the domain BacteriaEubacteria), microfossils of the domain Archaea have also been identified. Life was probably present throughout the Archean, but may have been limited to simple non-nucleated single-celled organisms, called Prokaryota (formerly known as Monera). "

Prokaryote (Wiki)
    "The prokaryotes ... are a group of organisms that lack a cell nucleus ... , or any other membrane-bound organelles. They differ from the eukaryotes, which have a cell nucleus. Most are unicellular, but a few prokaryotes such as myxobacteria have multicellular stages in their life cycles."   
The prokaryotes are divided into two domains: the bacteria and the archaea."  "The current model of the evolution of the first living organisms is that these were some form of prokaryotes, which may have evolved out of protobionts."   
The oldest known fossilized prokaryotes were laid down approximately 3.5 billion years ago, only about 1 billion years after the formation of the Earth's crust.
Bacteria and archaea reproduce through asexual reproduction, usually by binary fission or budding. Genetic exchange and recombination still occur, but this is a form of horizontal gene transfer and is not a replicative process, simply involving DNA being transferred between two cells, as in bacterial conjugation.
Prokaryotes have diversified greatly throughout their long existence ... leading to many highly distinct prokaryotic types. For example, in addition to using photosynthesis or organic compounds for energy, as eukaryotes do, prokaryotes may obtain energy from inorganic compounds such as hydrogen sulfide. This enables prokaryotes to thrive in harsh environments as cold as the snow surface of Antarctica, and as hot as undersea hydrothermal vents and land-based hot springs."

Archaea (Wiki) 
    "The origin of Archaea appears very old indeed and the archaeal lineage may be the most ancient that exists on earth.
Archaea are similar to bacteria in their general cell structure, but the composition and organization of some of these structures set the archaea apart. Like bacteria, archaea lack interior membranes so their cells do not contain organelles.[33] They also resemble bacteria in that their cell membrane is usually bounded by a cell wall and they swim by the use of one or more flagella.[51] In overall structure the archaea are most similar to gram-positive bacteria, as most have a single plasma membrane and cell wall, and lack a periplasmic space." 
Archaea exhibit a great variety of chemical reactions in their metabolism and use many different sources of energy. These forms of metabolism are classified into nutritional groups, depending on the source of energy and the source of carbon.
    Some archaea obtain their energy from inorganic compounds such as sulfur or ammonia (they are lithotrophs). These archaea include nitrifiers, methanogens and anaerobic methane oxidisers.[68] ... A common feature of all these reactions is that the energy released is used to generate adenosine triphosphate (ATP) through chemiosmosis, which is the same basic process that happens in the mitochondrion of animal cells.[69]
    Other groups of archaea use sunlight as a source of energy (they are phototrophs). However, oxygen-generating photosynthesis does not occur in any of these organisms.[69]  
    Many basic metabolic pathways are shared between all forms of life; for example, archaea use a modified form of glycolysis (the Entner–Doudoroff pathway) and either a complete or partial citric acid cycle.[70] These similarities with other organisms probably reflect both the early evolution of these parts of metabolism in the history of life and their high level of efficiency.

Archaea are genetically distinct from bacteria and eukaryotes, with up to 15% of the proteins encoded by any one archaeal genome being unique to the Archaea, although most of these unique genes have no known function.[94] ... The proteins that are shared between archaea, bacteria and eukaryotes form a common core of cell function, relating mostly to transcription, translation, and nucleotide metabolism.
Archaea reproduce asexually by binary or multiple fission, fragmentation, or budding; meiosis does not occur ..." 
Archaea exist in a broad range of habitats, and are a major part of global ecosystems,[7] and may contribute up to 20% of the total biomass on Earth.[105] Multiple archaeans are extremophiles, and historically this was seen as their ecological niche.[68] Indeed, some archaea survive high temperatures, often above 100 °C, as found in geysers, black smokers, and oil wells. Others are found in very cold habitats and others in highly saline, acidic, or alkaline water. However, other archaea are mesophiles that grow in much milder conditions, in marshland, sewage, the oceans, and soils.

Bacteria (Wiki)

Click image to enlarge. 

Cell structure of a bacterium, one of the two groups of prokaryotic life.

Some of the identified structures: 
    Cell Wall: 
    Plasma Membrane: 

The bacterial cell is surrounded by a lipid membrane, or cell membrane, which encloses the contents of the cell and acts as a barrier to hold nutrients, proteins and other essential components of the cytoplasm within the cell. As they are prokaryotes, bacteria do not tend to have membrane-bound organelles in their cytoplasm and thus contain few large intracellular structures. They consequently lack a nucleus, mitochondria, chloroplasts and the other organelles present in eukaryotic cells, such as the Golgi apparatus and endoplasmic reticulum."   
The general lack of internal membranes in bacteria means reactions such as electron transport occur across the cell membrane between the cytoplasm and the periplasmic space.

    "Bacteria are ubiquitous in every habitat on Earth, growing in soil, acidic hot springs, radioactive waste,[2] water, and deep in the Earth's crust, as well as in organic matter and the live bodies of plants and animals. There are typically 40 million bacterial cells in a gram of soil and a million bacterial cells in a millilitre of fresh water; in all, there are approximately five nonillion (5×1030) bacteria on Earth,[3] forming much of the world's biomass.

There are approximately ten times as many bacterial cells in the human flora of bacteria as there are human cells in the body, with large numbers of bacteria on the skin and as gut flora.
The ancestors of modern bacteria were single-celled microorganisms that were the first forms of life to develop on earth, about 4 billion years ago. For about 3 billion years, all organisms were microscopic, and bacteria and archaea were the dominant forms of life.
Bacteria often attach to surfaces and form dense aggregations called biofilms or bacterial mats. These films can range from a few micrometers in thickness to up to half a meter in depth, and may contain multiple species of bacteria, protists and archaea. Bacteria living in biofilms display a complex arrangement of cells and extracellular components, forming secondary structures such as microcolonies, through which there are networks of channels to enable better diffusion of nutrients.
Bacteria grow to a fixed size and then reproduce through binary fission, a form of asexual reproduction.[95] Under optimal conditions, bacteria can grow and divide extremely rapidly, and bacterial populations can double as quickly as every 9.8 minutes."   
Most bacteria have a single circular chromosome that can range in size from only 160,000 base pairs in the endosymbiotic bacteria Candidatus Carsonella ruddii,[104] to 12,200,000 base pairs in the soil-dwelling bacteria Sorangium cellulosum.[105]  ... The genes in bacterial genomes are usually a single continuous stretch of DNA and although several different types of introns do exist in bacteria, these are much more rare than in eukaryotes."   
Bacteria, as asexual organisms, inherit identical copies of their parent's genes (i.e., they are clonal). However, all bacteria can evolve by selection or changes to their genetic material DNA caused by genetic recombination or mutations ... Some bacteria also transfer genetic material between cells. This can occur in three main ways.  
    Firstly, bacteria can take up exogenous DNA from their environment, in a process called transformation.  
    Genes can also be transferred by the process of transduction, when the integration of a bacteriophage introduces foreign DNA into the chromosome.  
    The third method of gene transfer is bacterial conjugation, where DNA is transferred through direct cell contact. This gene acquisition from other bacteria or the environment is called horizontal gene transfer and may be common under natural condition

    Bacterial Cell Model (Goog)
    Good interactive animation, but can't copy-and-paste.  Click link.   

    Gram Positive Bacteria (Wiki) 
    The Gram positive bacteria are less complex than the Gram negative bacteria, and this inclines me to believe that they preceded the Gram negative bacteria in evolution.  Although there are numerous examples of more complex organisms evolving into less complex organisms, such loss of complexity always seems to be secondary to evolution from a complex, mobile, life-style to a less complex, immobile, life-style.  I don't see any sign of that here. 

    Gram Negative Bacteria (Wiki) 
    The Gram negative bacteria have an outer cell wall around the outside of an inner cell wall, and their inner cell wall seems identical to the single cell wall of the Gram positive bacteria.  So it looks like the Gram positive bacteria came first and they then developed the additional outer cell wall which makes them Gram negative.  Although this intuitive interpretation is challenged by some genetic evidence, genes are not transferred only from parent to child.  They can also be transferred by "lateral transfer" between bacteria which are not descended from one another. 

2003    Lateral gene transfer and the origins of prokaryote groups (Goog)   
"Lateral gene transfer (LGT) is now known to be a major force in the evolution of prokaryotic genomes. To date, most analyses have focused on either (a) verifying phylogenies of individual genes thought to have been transferred, or (b) estimating the fraction of individual genomes likely to have been introduced by transfer. Neither approach does justice to the ability of LGT to effect massive and complex transformations in basic biology. In some cases, such transformation will be manifested as the patchy distribution of a seemingly fundamental property (such as aerobiosis or nitrogen fixation) among the members of a group classically defined by the sharing of other properties (metabolic, morphological, or molecular, such as small subunit ribosomal RNA sequence). In other cases, the lineage of recipients so transformed may be seen to comprise a new group of high taxonomic rank ("class" or even "phylum"). Here we review evidence for an important role of LGT in the evolution of photosynthesis, aerobic respiration, nitrogen fixation, sulfate reduction, methylotrophy, isoprenoid biosynthesis, quorum sensing, flotation (gas vesicles), thermophily, and halophily. Sometimes transfer of complex gene clusters may have been involved, whereas other times separate exchanges of many genes must be invoked.

2006    Regulation of expression of the arabinose and glucose transporter genes in the thermophilic archeon Sulfolobss sulfataricus.   
    "Sugar uptake in Sulfolobus solfataricus, a thermoacidophilic archaeon, occurs through high-affinity binding of protein-dependent ABC transporters. We have investigated the expression patterns of two sugar transport operons, that is, the glucose and arabinose transporters. Analysis of the araS promoter activity, and the mRNA and protein levels in S. solfataricus cells grown on different carbon sources showed that expression of the arabinose transporter gene cluster is highly regulated and dependent on the presence of arabinose in the medium. Glucose in the growth medium repressed the expression of the arabinose transport genes. By means of primer extension, the transcriptional start site for the arabinose operon was mapped. Interestingly, expression of the arabinose transporter is down-regulated by addition of a selective set of amino acids to the medium. Expression of the glucose transporter genes appeared constitutive. These data confirm the earlier observation of a catabolite repression-like system in S. solfataricus.

2009    The Prokaryotic Origin and Evolution of Eukaryotic Chemosignaling Systems   
    "Analysis of our own results and data published over the last two decades supports the authors' hypothesis of the prokaryotic origin and endosymbiotic mechanism of appearance of chemosignaling systems in higher eukaryotes.  
    Comparison of the structural-functional organization of these information systems and their component blocks (receptors, GTP-binding proteins, enzymes with cyclase activity, protein kinases, etc.) in bacteria and eukaryotes revealed a whole series of similar characteristics pointing to evolutionary relatedness. This led to the conclusion that eukaryotic signal systems have prokaryotic roots.  
    In terms of their architecture and functional properties, the signal transduction systems seen in unicellular eukaryotes represent a transitional stage in the evolution of chemosignaling systems between prokaryotes and higher eukaryotes. The propagation of chemosignaling systems in three kingdoms - Bacteria, Archaea, and Eukarya - occurred by horizontal transfer of bacterial genes and the coevolution of the components of these systems."  
    My comment
This may lead to a discussion of LUCA-era hormones.  Unfortunately, the abstract doesn't offer any specific examples.  
    446 Similar articles  
    Note:  PubMed presented these similar articles "Sorted by Length", but I have rearranged them so they are now "Sorted by Publication Date".  However, this rearrangement must be reestablished every time the list is accessed.   
No Abstract, but a PDF.  Difficult to copy-and-paste.      
    "I wish to propose a hypothesis for the existence of stereospecificity in biological systems based upon intrinsic chemical properties of polynucleotide chains." 

Are archaebacteria merely derived 'prokaryotes'? 
The archaebacteria are a group of prokaryotes which seem as distinct from the true bacteria (eubacteria) as they are from eukaryotes. The evidence on which this conclusion rests is of two types: genotypic (quantitative)--that is, comparative sequence studies, and phenotypic (qualitative)--that is, differences in various organismal characteristics. The differences between archaebacteria and true bacteria are so great, both quantitatively and qualitatively, that the two bacterial groups should be considered as representing separate primary lines of descent, each tracing directly back to the universal ancestor. Furthermore, this ancestor itself seems not to be a prokaryote; rather it was a far simpler type of organism, one properly called a progenote. If this is true, the discovery of archaebacteria marks a major advance in the biologist's attempts to understand the basis for the evolution of the cell."  

Are messenger molecules in microbes the ancestors of the vertebrate hormones and tissue factors? 
Peptides very similar to hormones and other messenger molecules of vertebrates have been detected in extracts of unicellular eukaryotes (and prokaryotes). We present arguments to suggest the possibility that these molecules 1) originated evolutionarily in unicellular microbes, 2) serve as intercellular messenger molecules in these organisms, and 3) represent the phylogenetic ancestors of the hormones and neurotransmitters as well as paracrine and other tissue factors of the vertebrates. We suggest that the biochemical elements of intercellular communication arose very early in evolution and are highly conserved"  

Receptors for intercellular messenger molecules in microbes: similarities to vertebrate receptors and possible implications for diseases in man.
    No Abstract but 96 Similar articles:   

Prokaryotic mechanisms in eukaryotes: experimental data and speculations. 
Surprising experimental data recently provided could indicate ancestral genes common to mammals and bacteria. The detection of prokaryotic structures and/or mechanisms even in higher eukaryotes shows the extreme conservation of gene structures throughout evolution. The occurrence of common structures in pro- and eukaryotes is in good agreement with the new view concerning the early steps of cellular evolution."  

The evolution of hormonal signalling systems. 
1. A comparative analysis was made of chemosignalling systems responsible for the action of hormones, hormone-like substances, pheromones, etc. in vertebrates--multicellular invertebrates--unicellular eukaryotes. Many common features revealed in structural-functional organization of the above systems give evidence of their evolutionary conservatism.  
    2. It was shown that some molecular components as well as signal transduction mechanisms similar to those of higher eukaryote hormonal signalling systems are present in such early organisms as bacteria. This allowed a suggestion that the roots of chemosignalling systems are likely to be found in prokaryotes."  

Pathways of the evolution of hormonal signal realization systems. 
The problem of the structural-functional organization, and of the origin and evolution of the chemosignal systems which realize the effect of hormones and hormone-like substances in the higher eukaryotes-lower eukaryotes-prokaryotes series, is reviewed on the basis of an analysis of published information and our own data."  

Mammalian hormones in microbial cells. 
Hormones and hormone-binding proteins resembling those of vertebrates are widespread in fungi, yeast and bacteria. Functional responses of microbial cells to mammalian hormones have also been found. The evolutionary roots of the vertebrate endocrine system may, therefore, be far more ancient than is generally believed."  

The social behavior of myxobacteria.   
Myxobacteria are social microorganisms that undergo a spectacular cell cycle. Under starvation conditions, cells aggregate to certain points originating macroscopic fruiting bodies, inside which cells differentiate into myxospores. To accomplish this developmental cycle, cells must communicate. The signals that cells exchange during development as well as the signal transduction systems used by myxobacteria have been intensively studied during the last years.
    A family of eukaryotic-like protein serine/threonine kinases has been identified in Myxococcus xanthus, indicating that signal transduction systems similar to those used by eukaryotic cells may also function in myxobacteria."  

Do bacteria need to communicate with each other for growth? 
It is usually assumed that most prokaryotes, when given appropriate nutrients, can grow and divide in the absence of other cells of the same species. However, recent studies have suggested that, for growth, prokaryotes need to communicate with each other using signalling molecules, and a variety of 'eukaryotic' hormones have been shown to stimulate bacterial growth."  

The path from the RNA world. 
By focusing on the function of the protoribosome we develop a plausible model for the evolution of a protein-synthesizing ribosome from a high-fidelity RNA polymerase that incorporated triplets of oligonucleotides. With the standard assumption that during the evolution of enzymatic activity, catalysis is transferred from RNA --> RNP --> protein, the first proteins in the "breakthrough organism" (the first to have encoded protein synthesis) would be nonspecific chaperone-like proteins rather than catalytic. Moreover, because some RNA molecules that pre-date protein synthesis under this model now occur as introns in some of the very earliest proteins, the model predicts these particular introns are older than the exons surrounding them, the "introns-first" theory. Many features of the model for the genome organization in the final RNA world ribo-organism are more prevalent in the eukaryotic genome and we suggest that the prokaryotic genome organization (a single, circular genome with one center of replication) was derived from a "eukaryotic-like" genome organization (a fragmented linear genome with multiple centers of replication)."  

Signaling in unicellular eukaryotes. 
Intracellular systems have many common features in unicellular and multicellular organisms."  

Metabolic and membrane-altering toxins, molecular differentiation factors, and pheromones in the evolution and operation of endocrine-signalling systems. 
The endocrine systems of vertebrates and higher invertebrates may have evolved functionally from as far back on the evolutionary scale as bacteria and early multicellular organisms and their biological communities, which have been shown to produce a variety of cyclic nucleotides, peptides, fatty acids, prostaglandins and sterols with endocrine-altering effects in primative as well as more highly evolved species."  

[Phylogeny and evolution of hormone systems]. 
Studies on the potential origin and the evolution of cell-to-cell communication systems suggest that exocrine pheromones (food signals and toxins) might have been the primitive bioregulatory molecules of unicellular organisms for chemical communication with each other and with the biosphere. The broad distribution and the structural diversity of pheromones suggests that these molecules and their receptors were predecessor modules of cell communication systems in metazoa. Neurosecretory cells, as we find them in Cnidarians, possibly served as basic modules for the evolution of neurohormonal systems of higher animals. Studies on genetic model organisms, such as Drosophila or the mouse, have demonstrated that chemical communication between neighbouring or more distant cells does not just involve endocrine and neurosecretory cells, but also unexpectedly tissues and organs such as the heart or the adipose tissue (e. g. the leptin signalling pathway)."  

[Hormonal signal system of the lower eukaryotes]. 
On the basis of a comparative analysis of the primary structures of signal proteins in the lower and higher eukaryotes (G-protein alpha-subunits, enzymes-cyclases-adenylyl and guanylyl cyclases) some possible pathways of the evolution of proteins are suggested. At the level of unicellular organisms, the main blocks of hormone-sensitive signaling systems of the higher eukaryotes were created. Moreover, signaling systems of the lower eukaryotes ar more invariant than these of the higher eukaryotes."  

Hormone evolution: The key to signalling.   
    No Abstract, but 76 similar articles.   

Evolutionary connections between bacterial and eukaryotic signaling systems: a genomic perspective. 
Recent advances in microbial genomics suggest that several protein domains are common to bacterial and eukaryotic regulatory proteins. In particular, developmentally and morphologically complex prokaryotes appear to share several signaling modules with eukaryotes. New experimental studies and information from domain architectures point to several similar mechanistic themes in bacterial and eukaryotic signaling proteins. Laterally transferred protein domains, originally of bacterial provenance, appear to have contributed to the evolution of sensory pathways related to light, redox and nitric oxide signaling, and developmental pathways, such as Notch, cytokine and cytokinin signaling in eukaryotes."  

Molecular mechanisms of hormonal activity. I. Receptors. Neuromediators. Systems with second messengers.   
    Abstract doesn't say much, but 266 similar articles.   

304<446    Free PMC Article 
One-component systems dominate signal transduction in prokaryotes. 
Two-component systems that link environmental signals to cellular responses are viewed as the primary mode of signal transduction in prokaryotes. By analyzing information encoded by 145 prokaryotic genomes, we found that the majority of signal transduction systems consist of a single protein that contains input and output domains but lacks phosphotransfer domains typical of two-component systems. One-component systems are evolutionarily older, more widely distributed among bacteria and archaea, and display a greater diversity of domains than two-component systems."  

The cell type-specific signal proteins (pheromones) of protozoan ciliates.
In association with their mechanisms of self/non-self recognition (known as mating type systems), ciliates synthesize and constitutively secrete cell type-specific proteins into their extracellular medium. These proteins, designated as pheromones, have been isolated from species of Euplotes and shown to be members of families of structurally homologous molecules, all rich in intra-chain disulfide bonds and organized exclusively in helical conformation. Due to their similar architectures, they can interact with their membrane receptors in competition with one another and bind effectively to their cells of origin in autocrine fashion, or to other co-specific cells in paracrine fashion. In the former case, they promote the vegetative cell growth; in the latter, they induce cells to temporarily arrest their growth stage and shift to a mating (sexual) stage. These varied, context-dependent activities of ciliate pheromones imply an early evolution of basic properties of animal growth factors and cytokines in the unicellular eukaryotes."  

Interactions between bacteria and eukaryotes via small molecules. 
Recent developments in this field have focused on two areas: evidence has been gathered to show that secondary metabolites are often produced by symbiotic bacteria, rather than by the eukaryotic host, and the importance of bacterial cell-to-cell signalling in bacteria-host interactions has been confirmed."  

Protein superfamily evolution and the last universal common ancestor (LUCA). 
    See:  Last Universal (Common) Ancestor .

Evolution of prokaryotic two-component system signaling pathways: gene fusions and fissions. 
Two-component systems (TCSs) are common signal transduction systems, typically comprising paired histidine protein kinase (HK) and response regulator (RR) proteins. In many examples, it appears RR and HK genes have fused, producing a "hybrid kinase " We have characterized a set of prokaryotic genes encoding RRs, HKs, and hybrid kinases, enabling characterization of gene fusion and fission."  

Signaling systems of lower eukaryotes and their evolution. 
This review is devoted to the structural-functional organization of chemosignaling systems and their components in unicellular organisms such as Dictyostelium discoideum, yeasts and related fungi, flagellates, and ciliates."  

2008    220<446  
Hormonal imprinting: phylogeny, ontogeny, diseases and possible role in present-day human evolution.  
Hormonal imprinting is present already at the unicellular level causing the development of specific receptors and helping the easier recognition of useful or harmful surrounding molecules. The phenomenon is an important factor in the survival of the species, as the effect of imprinting is transmitted to the progeny cell generations."  

Interspecies and interkingdom communication mediated by bacterial quorum sensing. 
Quorum sensing (QS) has traditionally referred to a mechanism of communication within a species of bacteria. However, emerging research implicates QS in interspecies communication and competition, and such systems have been proposed in a wide variety of bacteria. This activity of bacterial QS also extends to relationships between bacteria and eukaryotes and host-pathogen interactions in both clinical and agricultural settings are of particular interest."  

[Procaryotic genesis and evolution of chemosignaling systems of eukaryotes]. 
The comparison of structural-functional organization of these information systems and their components (receptors, GTP-binding proteins, enzymes with cyclase activity, protein kinases etc.) in bacteria and eukaryotes revealed a number of similar features giving evidence for their evolutionary relationship. The conclusion was made that eukaryotic signaling systems have prokaryotic roots. The systems of signal transduction revealed in unicellular eukaryotes according to their architecture and functional properties represent a transient stage in the evolution of chemosignalling systems from prokaryotes to higher eukaryotes."  

Communication between microorganisms as a basis for production of virulence factors. 
Quorum sensing (QS), or cell-to-cell communication in bacteria, is achieved through the production and subsequent response to the accumulation of extracellular signal molecules called autoinductors. The main role of QS is regulation of production of virulence factors in bacteria. Bacterial pathogenicity is often manifested by the expression of various cell-associated and secreted virulence factors, such as exoenzymes, toxins and biofilm."  

Intercellular communication in bacteria. 
Bacteria have been long considered primitive organisms, with a lifestyle focused on the survival and propagation of single cells. However, in the past few decades it became obvious that bacteria can display sophisticated group behaviors. For instance, bacteria can communicate amongst themselves and with their hosts, by producing, sensing, and responding to chemical signals. By doing so, they can sense their surroundings and adapt as to increase their chances of survival and propagation."  

From pheromones to behavior. 
In recent years, considerable progress has been achieved in the comprehension of the profound effects of pheromones on reproductive physiology and behavior. Pheromones have been classified as molecules released by individuals and responsible for the elicitation of specific behavioral expressions in members of the same species. These signaling molecules, often chemically unrelated, are contained in body fluids like urine, sweat, specialized exocrine glands, and mucous secretions of genitals. The standard view of pheromone sensing was based on the assumption that most mammals have two separated olfactory systems with different functional roles: the main olfactory system for recognizing conventional odorant molecules and the vomeronasal system specifically dedicated to the detection of pheromones. However, recent studies have reexamined this traditional interpretation showing that both the main olfactory and the vomeronasal systems are actively involved in pheromonal communication."  

[Chemocommunication between bacteria and the higner vertebrate animals]. 
Between bacteria and the higher vertebrate animals there are close chemocommunicational connections that are realized via signal molecules secreted by bacteria, on the hand, and vertebrate hormones and hormone-like substances, on the other hand. The review presents data on regulatory effects of biogenic amines (catecholamines and serotonin), peptide hormones, and immunomodulators of the higher vertebrates on the vitally important functions of bacterial cells, their virulence and survivability. It has been shown that some bacterial signal molecules, such as N-acylated derivatives of homoserinelactones, also are able to regulate fundamental cellular processes in the higher vertebrates."  

The prokaryotic origin and evolution of eukaryotic chemosignaling systems. 
Analysis of our own results and data published over the last two decades supports the authors' hypothesis of the prokaryotic origin and endosymbiotic mechanism of appearance of chemosignaling systems in higher eukaryotes. Comparison of the structural-functional organization of these information systems and their component blocks (receptors, GTP-binding proteins, enzymes with cyclase activity, protein kinases, etc.) in bacteria and eukaryotes revealed a whole series of similar characteristics pointing to evolutionary relatedness. This led to the conclusion that eukaryotic signal systems have prokaryotic roots. In terms of their architecture and functional properties, the signal transduction systems seen in unicellular eukaryotes represent a transitional stage in the evolution of chemosignaling systems between prokaryotes and higher eukaryotes. The propagation of chemosignaling systems in three kingdoms - Bacteria, Archaea, and Eukarya - occurred by horizontal transfer of bacterial genes and the coevolution of the components of these systems."  

50<446     Free Article   
Cell-cell signalling in bacteria: not simply a matter of quorum. 
Bacterial signalling known as quorum sensing (QS) relies on the synthesis of autoinducing signals throughout growth; when a threshold concentration is reached, these signals interact with a transcriptional regulator, allowing the expression of specific genes at a high cell density. One of the most studied intraspecies signalling is based on the use of N-acyl-homoserine lactones (AHL). Many factors other than cell density were shown to affect AHL accumulation and interfere with the QS signalling process. At the cellular level, the genetic determinants of QS are integrated in a complex regulatory network, including QS cascades and various transcriptional and post-transcriptional regulators that affect the synthesis of the AHL signal. In complex environments where bacteria exist, AHL do not accumulate at a constant rate; the diffusion and perception of the AHL signal outside bacterial cells can be compromised by abiotic environmental factors, by members of the bacterial community such as AHL-degrading bacteria and also by compounds produced by eukaryotes acting as an AHL mimic or inhibitor."  

Impact of genome reduction on bacterial metabolism and its regulation. 
To understand basic principles of bacterial metabolism organization and regulation, but also the impact of genome size, we systematically studied one of the smallest bacteria, Mycoplasma pneumoniae. A manually curated metabolic network of 189 reactions catalyzed by 129 enzymes allowed the design of a defined, minimal medium with 19 essential nutrients. More than 1300 growth curves were recorded in the presence of various nutrient concentrations. Measurements of biomass indicators, metabolites, and 13C-glucose experiments provided information on directionality, fluxes, and energetics; integration with transcription profiling enabled the global analysis of metabolic regulation. Compared with more complex bacteria, the M. pneumoniae metabolic network has a more linear topology and contains a higher fraction of multifunctional enzymes; general features such as metabolite concentrations, cellular energetics, adaptability, and global gene expression responses are similar, however."   

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