01.24 Prokaryote Colonies

The Evolutionary History of Quorum-Sensing Systems in Bacteria (Goog) 
Full length article available online for free. 

Chemosensory pathways, motility and development in Myxococcus xanthus (Goog) 
Full length PDF.  Unfortunately, the link doesn't always work.  When it doesn't, the paper can be accessed by searching for the title in Google and then clicking on Google's link. 

"The complex life cycle of Myxococcus xanthus includes predation, swarming, fruiting-body formation and sporulation." 

"M. xanthus grow by scavenging nutrients from decomposing soil and detritus, or by predation of other microorganisms."  "When M. xanthus swarms cannot find sufficient nutrients or prey, they enter a developmental pathway that results in the formation of multicellular mounds, which develop into fruiting bodies." 

Detection, purification and characterisation of quorum sensing signal molecules... (PubMed) 
"Quorum sensing (also called autoinduction) is a term that describes an environmental sensing system that allows bacteria to monitor their own population density. Autoinduction relies upon the interaction of a small diffusible signal molecule (the autoinducer) with a transcriptional activator protein to couple gene expression with cell population density. These signal molecules diffuse from bacterial cells and accumulate in the environment as a function of cell growth. Once a threshold concentration is reached, these signals serve as co-inducers to regulate the transcription of (a) set(s) of target genes. In Gram-negative bacteria, most autoinducers belong to the family of N-acylhomoserine lactones (AHLs).

N-Acyl homoserine lactone (Wiki) 
Here's what they look like.  Click on the image to enlarge. 
General chemical structure of an N-acyl homoserine lactone 

"Signaling molecules are produced within the cell and are released into the environment. The resulting concentration of signaling molecules in the environment is dependent upon population density. Once the population density has reached a particular threshold, gene expression can begin. This allows bacteria to coordinate group-based behavior.

N-AHL's produced by different bacteria differ in the length of the R-group side chain. Chain lengths vary from 4 to 18 carbon  atoms and in the substitution of a carbonyl  at the third carbon." 

Convergence of hormones and autoinducers at the host/pathogen interface (Goog-PubMed) 
From the abstract:  "Acyl homoserine lactone (AHL) autoinducers are fatty acid-based signaling molecules synthesized by several Gram-negative bacteria that are used to coordinate gene expression in a process termed "quorum sensing" (QS)."  "... autoinducers, which exhibit structural and functional similarities to mammalian lipid-based hormones ..."  "Here we will compare and contrast bacterial QS systems with eukaryotic endocrine systems ...

From the PDF:  "Recent evidence shows that autoinducers not only control gene expression in bacterial cells, but also alter gene expression in mammalian cells. These alterations include modulation of proinflammatory cytokines and induction of apoptosis. Some of
these responses may have deleterious effects on the host’s immune response, thereby leading to increased bacterial pathogenesis." 
"... autoinducers ... exhibit structural and functional similarities to mammalian lipid-based hormones ..." 
(This reference also given in Section 09.11.) 

Quorum sensing in bacteria (PubMed) 
Only abstract public, but I have PDF. 
Quorum sensing bacteria produce and release chemical signal molecules called autoinducers that increase in concentration as a function of cell density. The detection of a minimal threshold stimulatory concentration of an autoinducer leads to an alteration in gene expression. Gram-positive and Gram-negative bacteria use quorum sensing communication circuits to regulate a diverse array of physiological activities. These processes include symbiosis, virulence, competence, conjugation, antibiotic production, motility, sporulation, and biofilm formation. In general, Gram-negative bacteria use acylated homoserine lactones as autoinducers, and Gram-positive bacteria use processed oligo-peptides to communicate."   

Oligopeptide (Wiki) 
An oligopeptide (oligo-, "few") consists of between 2 and 20 amino acids. (includes dipeptides, tripeptides, tetrapeptides, pentapeptides, etc.)

Hormone fatty acid modifications: Gram negative bacteria and vertebrates demonstrate common structure and function (Goog)
Abstract only, but I have PDF. 
Bacteria are known to regulate diverse physiological processes through a mechanism called quorum sensing (QS). Prokaryotes communicate by extracellular signalling compounds, i.e. autoinducers (acyl homoserine lactone, AHL of Gram negative bacteria) or pheromones (post-translationally modified peptides of Gram positive bacteria), which activate genetic pathways when they reach a sufficient concentration (QS)."  "In vertebrates ... growth hormone (GH) ... release is stimulated by hypothalamic GH-releasing hormone (GHRH) and ghrelin (endogenous ligand of the GHS-receptor, GHS-R). Ghrelin is a 28-amino acid peptide"  (Also referenced in Section 09.11.) 

Pheromone (Goog-Wiki) 

Quorum sensing: the many languages of bacteria (PubMed) 
Abstract only, but I have full length HTML. 
bacteria communicate with each other through small 'hormone-like' organic compounds referred to as autoinducers."  "Three major quorum-sensing circuits have been described: one used primarily by Gram-negative bacteria, one used primarily by Gram-positive bacteria, and one that has been proposed to be universal.

Thinking about Bacterial Populations as Multicellular Organisms (PubMed) 
Abstract only.  "Intercellular communication and multicellular coordination are now known to be widespread among prokaryotes... Bacteria have sophisticated signal transduction networks for integrating intercellular signals with other information to make decisions about gene expression and cellular differentiation...Bacteria benefit from multicellular cooperation by using cellular division of labor, accessing resources that cannot effectively be utilized by single cells, collectively defending against antagonists, and optimizing population survival by differentiating into distinct cell types.

Quorum Sensing and Swarming Migration in Bacteria (PubMed) 
Abstract only.  "Bacterial cells can produce and sense signal molecules, allowing the whole population to initiate a concerted action...


Bacterial swarming: an example of prokaryotic differentiation and multicellular behavior  (PubMed) 
"Bacterial swarming involves the differentiation of vegetative cells into hyperflagellated swarm cells which undergo cycles of rapid and coordinated population migration across solid surfaces.

Living on a surface: swarming and biofilm formation (PubMed) 
"Swarming is the fastest known bacterial mode of surface translocation and enables the rapid colonization of a nutrient-rich environment and host tissues. This complex multicellular behavior requires the integration of chemical and physical signals, which leads to the physiological and morphological differentiation of the bacteria into swarmer cells.

Signals, regulatory networks, and materials that ... biofilms (PubMed)
"Our current understanding of biofilm formation is based on numerous studies of myriad bacterial species. Here, we review a portion of this large body of work including the environmental signals and signaling pathways that regulate biofilm formation, the components of the biofilm matrix, and the mechanisms and regulation of biofilm dispersal.

Quorum sensing by peptide pheromones and two-component
signal-transduction systems in Gram-positive bacteria. (Goog) 
Full length PDF.