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Many species of Proteobacteria communicate by using LuxI-LuxR-type quorum-sensing systems that produce and detect acyl-homoserine lactone (acyl-HSL) signals. Most of the known signals are straight-chain fatty acyl-HSLs, and evidence indicates that LuxI homologs prefer fatty acid-acyl carrier protein (ACP) over fatty acyl-CoA as the acyl substrate for signal synthesis. Two related LuxI homologs, RpaI and BtaI from Rhodopseudomonas palustris and photosynthetic stem-nodulating bradyrhizobia, direct production of the aryl-HSLs p-coumaroyl-HSL and cinnamoyl-HSL, respectively. Here we report that BjaI from the soybean symbiont Bradyrhizobium japonicum USDA110 is closely related to RpaI and BtaI and catalyzes the synthesis of isovaleryl-HSL (IV-HSL), a branched-chain fatty acyl-HSL. We show that IV-HSL induces expression of bjaI, and in this way IV-HSL functions like many other acyl-HSL quorum-sensing signals. Purified histidine-tagged BjaI was an IV-HSL synthase, which was active with isovaleryl-CoA but not detectably so with isovaleryl-ACP. This suggests that the RpaI-BtaI-BjaI subfamily of acyl-HSL synthases may use CoA- rather than ACP-linked substrates for acyl-HSL synthesis. The bjaI-linked bjaR1 gene is involved in the response to IV-HSL, and BjaR1 is sensitive to IV-HSL at concentrations as low as 10 pM. Low but sufficient levels of IV-HSL (about 5 nM) accumulate in B. japonicum culture fluid. The low levels of IV-HSL synthesis have likely contributed to the fact that the quorum-sensing signal from this bacterium has not been described elsewhere. [ABSTRACT FROM AUTHOR]

Quorum sensing in the bacterium Rhodopseudomonas palustris involves the Rpal signal synthase, which produces p-coumaroylhomoserine lactone (pC-HSL) and RpaR, which is a pC-HSL-dependent transcriptional activator. There is also an antisense rpaR transcript {asrpaR) of unknown function. Recent RNAseq studies have revealed that bacterial antisense RNAs are abundant, but little is known about the function of these molecules. Because asrpaR expression is quorum sensing dependent, we sought to characterize its production and function. We show that asrpaR is approximately 300-600 bases and is produced in response to pC-HSL and RpaR. There is an RpaR-binding site centered 51.5 bp from the mapped asrpaR transcript start site. We show that asrpaR overexpression reduces RpaR levels, rpal expression, and pC-HSL production. We also generated an asrpaR mutant, which shows elevated RpaR levels, and elevated rpal expression. Thus, asrpaR inhibits rpaR translation, and this inhibition results in suppression of RpaR-dependent rpal expression and, thus, pC-HSL production. The R. palustris asrpaR represents an antisense RNA for which an activity can be measured and for which a distinct regulatory circuit related to a function is elucidated. It also represents yet another subtle regulatory layer for acyl-homoserine lactone quorum-sensing signal-responsive transcription factors. [ABSTRACT FROM AUTHOR]

Quorum-sensing (QS) systems allow organisms, such as the pathogen Pseudomonas aeruginosa, to link gene expression with their population density and the diffusion and flow characteristics of their environment. The leading hypotheses about QS systems' biological functions necessitate that QS-controlled gene expression be suppressed until a threshold culture density (the quorum) is reached. Despite a detailed understanding of QS in P. aeruginosa, known regulatory elements do not fully explain how the quorum threshold for gene activation is produced. Here we investigated the mechanism with a screening approach that used random gene activation. These experiments uncovered a regulator without close homologs in other species that produces the quorum expression threshold. Expression of this regulator (named QteE) reduces LasR protein stability without affecting LasR transcription or translation. QteE also independently reduces RhIR levels. Because QteE can block QS when signal levels are high, it could provide a mechanism for individual cells to exert autonomous control over their QS regulons. This unique regulator governs two central QS control points in P. aeruginosa and shapes the expression pattern thought funda- mental to the biological functions of QS. [ABSTRACT FROM AUTHOR]

Mechanisms for controlling symbiont populations are critical for maintaining the associations that exist between a host and its microbial partners. We describe here the transcriptional, metabolic, and ultrastructural characteristics of a diel rhythm that occurs in the symbiosis between the squid Euprymna scolopes and the luminous bacterium Vibrio fischeri. The rhythm is driven by the host's expulsion from its light-emitting organ of most of the symbiont population each day at dawn. The transcriptomes of both the host epithelium that supports the symbionts and the symbiont population itself were characterized and compared at four times over this daily cycle. The greatest fluctuation in gene expression of both partners occurred as the day began. Most notable was an up-regulation in the host of >50 cytoskeleton-related genes just before dawn and their subsequent down regulation within 6 h. Examination of the epithelium by TEM revealed a corresponding restructuring, characterized by effacement and blebbing of its apical surface. After the dawn expulsion, the epithelium reestablished its polarity, and the residual symbionts began growing, repopulating the light organ. Analysis of the symbiont transcriptome suggested that the bacteria respond to the effacement by up-regulating genes associated with anaerobic respiration of glycerol; supporting this finding, lipid analysis of the symbionts' membranes indicated a direct incorporation of host-derived fatty acids. After 12 h, the metabolic signature of the symbiont population shifted to one characteristic of chitin fermentation, which continued until the following dawn. Thus, the persistent maintenance of the squid-vibrio symbiosis is tied to a dynamic diel rhythm that involves both partners. [ABSTRACT FROM AUTHOR]

The article offers information on a report which presents a meta-analysis tool that analyzes sequence and expression data, and reveals a flexible cis-regulatory code underlying a complex honey bee behavioral maturation. It reflects that the tool will help the scientists for conducting integrative analyses of the multitude of generated datasets. It provides information that complex phenotypes are produced by a multitude of heritable and environmental determinants.