Cell-to-cell communication in bacteria is mediated by quorum-sensing systems (QSS) that produce chemical signal molecules called autoinducers (AI).In particular, LuxS/AI-2-dependent QSS has been proposed to act as a universal lexicon that mediates intra-and interspecific bacterial behavior. Here we report that the model organism Bacillus subtilis operates a luxS-dependent QSS that regulates its morphogenesis and social behavior. We demonstrated that B. subtilis luxS is a growth-phase-regulated gene that produces active AI-2 able to mediate the interspecific activation of light production in Vibrio harveyi. We demonstrated that in B. subtilis, luxS expression was under the control of a novel AI-2-dependent negative regulatory feedback loop that indicated an important role for AI-2 as a signaling molecule. Even though luxS did not affect spore development, AI-2 production was negatively regulated by the master regulatory proteins of pluricellular behavior, SinR and Spo0A. Interestingly, wild B. subtilis cells, from the undomesticated and probiotic B. subtilis natto strain, required the LuxS-dependent QSS to form robust and differentiated biofilms and also to swarm on solid surfaces. Furthermore, LuxS activity was required for the formation of sophisticated aerial colonies that behaved as giant fruiting bodies where AI-2 production and spore morphogenesis were spatially regulated at different sites of the developing colony. We proposed that LuxS/AI-2 constitutes a novel form of quorumsensing regulation where AI-2 behaves as a morphogen-like molecule that coordinates the social and pluricellular behavior of B. subtilis.Bacteria not only behave as self-sufficient individuals but also act as communities capable of cell-cell communication (7,15,20,42,53). This social interaction leads to the coordination of communitarian activities that resemble, in their complexity, the behaviors observed in multicellular organisms (20,42,49,53,57). This microbial phenomenon is known as quorum sensing, a process by which bacteria monitor their cell population density by measuring the concentration of small secreted signal molecules called autoinducers (57). Even though a vast number of diverse quorum-sensing systems exist (41, 46, 57), they can be divided into two established paradigms that regulate the intraspecific behavior in many bacteria: (i) LuxI/LuxR-type quorum-sensing systems in gram-negative bacteria responsible for the production of N-acyl-L-homoserine lactone autoinducers or type I autoinducers and (ii) oligopeptide/two component-type quorum-sensing circuits in gram-positive bacteria responsible for the production of autoinducer peptides (4,17,26,32,44).However, in recent years, a considerable amount of information has been gained on the existence of another type of quorum-sensing system that not only seems to participate in intraspecific bacterial behavior but also seems to regulate the interspecific interactions among bacteria of different genera. This system involves the production of autoinducer-2 (AI-2) signal molecul...

Even though there is a large body of information concerning the harmful effects of alcohol on different organisms, the mechanism(s) that affects developmental programs, at a single-cell level, has not been clearly identified. In this respect, the spore-forming bacterium Bacillus subtilis constitutes an excellent model to study universal questions of cell fate, cell differentiation, and morphogenesis. Here, we demonstrate that treatment with subinhibitory concentrations of alcohol that did not affect vegetative growth inhibited the initiation of spore development through a selective blockage of key developmental genes under the control of the master transcription factor Spo0AϳP. Isopropyl-␤-D-thiogalactopyranoside-directed expression of a phosphorylationindependent form of Spo0A (Sad67) and the use of an in vivo mini-Tn10 insertional library permitted the identification of the developmental SinR repressor and RapA phosphatase as the effectors that mediated the inhibitory effect of alcohol on spore morphogenesis. A double rapA sinR mutant strain was completely resistant to the inhibitory effects of different-C-length alcohols on sporulation, indicating that the two cell fate determinants were the main or unique regulators responsible for the spo0 phenotype of wild-type cells in the presence of alcohol. Furthermore, treatment with alcohol produced a significant induction of rapA and sinR, while the stationary-phase induction of sinI, which codes for a SinR inhibitor, was completely turned off by alcohol. As a result, a dramatic repression of spo0A and the genes under its control occurred soon after alcohol addition, inhibiting the onset of sporulation and permitting the evaluation of alternative pathways required for cellular survival.

Finger millet (Elucine corocana), locally known as ragi, and probiotics have been recognized for their health benefits. In the present work we describe novel probiotic ragi malt (functional food) that has been prepared using ragi and probiotic Leuconostoc mesenteroides (Lm) and Bacillus subtilis natto (Bs), alone and in combination, for antagonistic activity against Vibrio cholerae (Vc). In vitro studies using pure cultures showed that each probiotic strain (Lm or Bs) was able to inhibit the planktonic growth of Vc as well as its ability to make biofilms and adhere to extracellular matrix proteins (fibronectin, Fn) that may function in vivo as initial ports of entrance of the pathogen. Interestingly, the combination of both probiotic strains (Lm plus Bs) produced the strongest activity against the Vc. When both cultures were used together in the ragi malt the antimicrobial activity against Vc was enhanced due to synergistic effect of both probiotic strains. The inclusion of both probiotic strains in the functional food produced higher amounts of beneficial fatty acids like linoleic and linolenic acid and increased the mineral content (iron and zinc). The viability and activity of Lm and Bs against Vc was further enhanced with the use of adjuvants like ascorbic acid, tryptone, cysteine hydrochloride and casein hydrolysate in the ragi malt. In sum, the intake of probiotic ragi malt supplemented with Lm and Bs may provide nutrition, energy, compounds of therapeutic importance and antagonistic activity against Vc to a large extent to the consumer.