Showing papers by "Stephen C. Winans published in 2016"
12 Aug 2016
TL;DR: It has become perhaps too widely accepted that pheromones enable bacteria to estimate their population density, a process sometimes referred to as quorum sensing, and a variety of signals have been described.
Abstract: The past 15 years have seen a revolution in our understanding of how bacteria use pheromones to communicate and coordinate their physiologies. Bacteria synthesize and detect a rich variety of diffusible chemical signals that impact diverse behaviours, including bioluminescence, horizontal DNA transfer, biofilm formation, pathogenesis, and the production of antimicrobials and other secondary metabolites (Ng and Bassler, 2009; Pappas et al., 2004; Waters and Bassler, 2005; Winans, 2011; see also Chapter 2.18). In fact, entirely new classes of pheromones have been described in the past few years (discussed further in this chapter), and more will likely be described in the near future. It has become perhaps too widely accepted that pheromones enable bacteria to estimate their population density, a process sometimes referred to as quorum sensing. Importantly, these signals allow large numbers of bacteria to act in synchrony, which perhaps blurs the distinction between single cells and multicellular organisms. Several classes of diffusible signals, or pheromones, have been described in bacteria. Communication among the members of the Firmicutes often requires oligopeptides that are synthesized on ribosomes and processed by proteolysis during export (Cook and Federle, 2014; Monnet et al., 2014; Singh and Ray, 2014). Some of these peptides are cyclized or otherwise covalently modified. Some are detected by membranespanning two-component kinases, while others are imported into the cytoplasm and detected by cytoplasmic receptors. An entirely different class of signaling molecules has evolved in the Actinobacteria, including Streptomyces spp. and their allies. These molecules are collectively referred to as γ-butyrolactones and include the A-factor of S. coelicolor. These signals play important roles in secondary metabolism and cell differentiation (Liu et al., 2013). Signaling among Proteobacteria appears to have evolved several times independently, and a variety of signals have been described. One type of signal used by a variety of Proteobacteria are long-chain fatty acids that are generally monounsaturated, branched, or both (Deng et al., 2011). The founding member of this family of signals is DSF (diffusible signaling factor, or cis-11methyl-2-dodecenoic acid), and it was found in Xanthomonas campestris. The genes required for synthesis and detection of similar signals are widely distributed throughout the Proteobacteria. Another family of signals found in diverse Proteobacteria are composed α-hydroxyketones (AHK), exemplified by Cholera autoinducer-1 (CAI-1, or 3-hydroxytridecan-4-one) and Legionella autoinducer-1 (LAI-1, or 3-hydroxypentadecan4-one) (Pereira et al., 2013; Tiaden and Hilbi, 2012; Tiaden et al., 2010). Another signal, denoted autoinducer-2 (AI2), is synthesized by many species of bacteria, and might therefore serve as an intergeneric signal (Pereira et al., 2013), though it remains possible that some of the bacteria that make AI2 may simply excrete it as a waste product rather than use it as a signal. Yet another family of signals that are distributed throughout the Proteobacteria are denoted N-acylhomoserine lactones (AHLs), and they have identical homoserine lactone head groups and a variety of hydrophobic acyl groups that differ in length, oxidation, and desaturation (Ng and Bassler, 2009; Waters and Bassler, 2005). Though most AHLs have straight chain acyl groups, a few have branched chains or aromatic groups (Ahlgren et al., 2011; Lindemann et al., 2011; Schaefer et al., 2008). The first described member of this family is OHHL (N-3-oxohexanoyl-l-homoserine lactone) of the marine bioluminescent bacterium Allivibrio fischeri. OHHL is synthesized by LuxI and detected by the OHHL-dependent transcription factor LuxR (Eberhard et al., 1981; Engebrecht et al., 1983). LuxR has two domains, an N-terminal domain (NTD) that binds pheromone, and a C-terminal domain (CTD) that binds DNA
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