All organisms that produce fatty acids do so via a repeated cycle of reactions. In mammals and other animals, these reactions are catalyzed by a type I fatty acid synthase (FAS), a large multifunctional protein to which the growing chain is covalently attached. In contrast, most bacteria (and plants) contain a type II system in which each reaction is catalyzed by a discrete protein. The pathway of fatty acid biosynthesis in Escherichia coli is well established and has provided a foundation for elucidating the type II FAS pathways in other bacteria (White et al., 2005). However, fatty acid biosynthesis is more diverse in the phylum Actinobacteria: Mycobacterium, possess both FAS systems while Streptomyces species have only the multi-enzyme FAS II system and Corynebacterium species exclusively FAS I. In this review we present an overview of the genome organization, biochemical properties and physiological relevance of the two FAS systems in the three genera of actinomycetes mentioned above. We also address in detail the biochemical and structural properties of the acyl-CoA carboxylases (ACCases) that catalyzes the first committed step of fatty acid synthesis in actinomycetes, and discuss the molecular bases of their substrate specificity and the structure-based identification of new ACCase inhibitors with anti-mycobacterial properties.

The terminal reaction in triacylglyceride (TAG) biosynthesis is the esterification of diacylglycerol (DAG) with a fatty acid molecule. To study this reaction in Streptomyces coelicolor, we analyzed three candidate genes (sco0958, sco1280, and sco0123) whose products significantly resemble the recently identified wax ester synthase/acyl-coenzyme A (CoA):DAG acyltransferase (DGAT) from Acinetobacter baylyi. The deletion of either sco0123 or sco1280 resulted in no detectable decrease in TAG accumulation. In contrast, the deletion of sco0958 produced a dramatic reduction in neutral lipid production, whereas the overexpression of this gene yielded a significant increase in de novo TAG biosynthesis. In vitro activity assays showed that Sco0958 mediates the esterification of DAG using long-chain acyl-CoAs (C 14 to C 18 ) as acyl donors. The K m and V max values of this enzyme for myristoyl-CoA were 45 M and 822 nmol mg ؊1 min ؊1 , respectively. Significantly, the triple mutant strain was not completely devoid of storage lipids, indicating the existence of alternative TAG-biosynthetic routes. We present strong evidence demonstrating that the residual production of TAG in this mutant strain is mediated, at least in part, by an acyl-CoA-dependent pathway, since the triple mutant still exhibited DGAT activity. More importantly, there was substantial phospholipid:DGAT (PDAT) activity in the wild type and in the triple mutant. This is the first time that a PDAT activity has been reported for bacteria, highlighting the extreme metabolic diversity of this industrially important soil microorganism.Triacylglycerols (TAGs) are the most common lipid-based energy reserves in animals, plants, and eukaryotic microorganisms (3). In bacteria, the most abundant class of neutral lipids are polyhydroxyalkanoic acids (3), but a few examples of substantial TAG accumulation have been reported, mainly in the actinomycetes Mycobacterium (4), Nocardia (1), Rhodococcus (2), and Streptomyces (27). Furthermore, the biosynthesis of wax esters (WEs) (oxoesters of long-chain primary fatty alcohols and long-chain fatty acids) has been frequently reported for members of the genus Acinetobacter (23). Recently, storage lipid accumulation in the hydrocarbonoclastic marine bacterium Alcanivorax borkumensis was reported (19), representing the first example of significant TAG accumulation in a gramnegative prokaryote.Three different classes of enzymes are known to mediate TAG formation from diacylglycerol (DAG) (22). Acyl-coenzyme A (CoA):DAG acyltransferase (DGAT) catalyzes the acylation of DAG using acyl-CoAs as substrates. In eukaryotes, two DGAT families (DGAT1 and DGAT2) with no sequence resemblance to each other have been identified and characterized. Members of the DGAT1 gene family were found in animals and plants (7,16,31), whereas members of the DGAT2 gene family are found in animals (8), plants (5), and Saccharomyces cerevisiae (32). Acyl-CoA-independent TAG synthesis in yeast and plants is mediated by a phospholipid (PL):DGAT (PDAT) that uses PLs...

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...

SummaryCompartmentalized gene expression during sporulation is initiated after asymmetric division by cell-specific activation of the transcription factors s s s s F and s s s s E . Synthesis of these s s s s factors, and their regulatory proteins, requires the activation (phosphorylation) of Spo0A by the phosphorelay signalling system. We report here a novel regulatory function of the antianti-s s s s F SpoIIAA as inhibitor of Spo0A activation. This effect did not require s s s s F activity, and it was abolished by expression of the phosphorelay-independent form Spo0A-Sad67 indicating that SpoIIAA directly interfered with Spo0A ~ P generation. IPTG-directed synthesis of the SpoIIE phosphatase in a strain carrying a multicopy plasmid coding for SpoIIAA and its specific inhibitory kinase SpoIIAB blocked Spo0A activation suggesting that the active form of the inhibitor was SpoIIAA and not SpoIIAA-P. Furthermore, expression of the non-phosphorylatable mutant SpoIIAAS58A (SpoIIAA-like), but not SpoIIAAS58D (SpoIIAA-P-like), completely blocked Spo0A-dependent gene expression. Importantly, SpoIIAA expressed from the chromosome under the control of its normal spoIIA promoter showed the same negative effect regulated not only by SpoIIAB and SpoIIE but also by septum morphogenesis. These findings are discussed in relation to the potential contribution of this novel inhibitory feedback with the proper activation of s s s s F and s s s s E during development.

The participation of the Xanthomonas axonopodis pv. citri hypersensitive response and pathogenicity ( hrp ) cluster in interactions with host and nonhost plants was characterized in pathogenicity and avirulence models. The hrp cluster encodes the type III secretion system indispensable for trafficking of proteins to the plant cell. Mutations in operons hrpB and hrpD and the hrpF gene failed to produce canker in citrus plants or hypersensitive response in cotton plants. The interaction of the phytopathogen with various nonhost plants has been characterized. The results showed that the hypersensitive response is activated in leaves of cotton, bean, tobacco, tomato, pepper and Nicotiana benthamiana , and that genes present in operons hrpB and hrpD and the hrpF gene are required for pathogenicity in hosts and induction of the hypersensitive response in nonhost plants.

Surfactin is a lipoheptapeptide produced by several Bacillus species and identified for the first time in 1969. At first, the biosynthesis of this remarkable biosurfactant was described in this review. The peptide moiety of the surfactin is synthesized using huge multienzymatic proteins called NonRibosomal Peptide Synthetases. This mechanism is responsible for the peptide biodiversity of the members of the surfactin family. In addition, on the fatty acid side, fifteen different isoforms (from C12 to C17) can be incorporated so increasing the number of the surfactin-like biomolecules. The review also highlights the last development in metabolic modeling and engineering and in synthetic biology to direct surfactin biosynthesis but also to generate novel derivatives. This large set of different biomolecules leads to a broad spectrum of physico-chemical properties and biological activities. The last parts of the review summarized the numerous studies related to the production processes optimization as well as the approaches developed to increase the surfactin productivity of Bacillus cells taking into account the different steps of its biosynthesis from gene transcription to surfactin degradation in the culture medium.

SummaryMembrane lipid homeostasis is essential for bacterial survival and adaptation to different environments. The regulation of fatty acid biosynthesis is therefore crucial for maintaining the correct composition and biophysical properties of cell membranes. This regulation implicates a biochemical control of key enzymes and a transcriptional regulation of genes involved in lipid metabolism. In Streptomyces coelicolor we found that control of lipid homeostasis is accomplished, at least in part, through the transcriptional regulation of fatty acid biosynthetic genes. A novel transcription factor, FasR (SCO2386), controls expression of fabDHPF operon and lies immediately upstream of fabD, in a cluster of genes that is highly conserved within actinomycetes. Disruption of fasR resulted in a mutant strain, with severe growth defects and a delay in the timing of morphological and physiological differentiation. Expression of fab genes was downregulated in the fasR mutant, indicating a role for this transcription factor as an activator. Consequently, the mutant showed a significant drop in fatty acid synthase activity and triacylglyceride accumulation. FasR binds specifically to a DNA sequence containing fabDHPF promoter region, both in vivo and in vitro. These data provide the first example of positive regulation of genes encoding core proteins of saturated fatty acid synthase complex.

Rhodococcus opacus PD630 is an oleaginous bacterium able to accumulate large amounts of triacylglycerols (TAG) in different carbon sources. The last reaction for TAG biosynthesis is catalyzed by the bifunctional wax ester synthase/acyl-CoA:diacylglycerol acyltransferase (WS/DGAT) enzymes encoded by atf genes. R. opacus PD630 possesses at least 17 putative atf homologous genes in its genome, but only atf1 and atf2 exhibited a significant DGAT activity when expressed in E. coli, as revealed in a previous study. The contribution of atf1 gene to TAG accumulation by strain PD630 has been demonstrated previously, although additional Atfs may also contribute to lipid accumulation, since the atf1-disrupted mutant is still able to produce significant amounts of TAG (Alvarez et al., Microbiology 154:2327-2335, 2008). In this study, we investigated the in vivo role of atf2 gene in TAG accumulation by R. opacus PD630 by using different genetic strategies. The atf2-disrupted mutant exhibited a decrease in TAG accumulation (up to 25-30 %, w/w) and an approximately tenfold increase in glycogen formation in comparison with the wild-type strain. Surprisingly, in contrast to single mutants, a double mutant generated by the disruption of atf1 and atf2 genes only showed a very low effect in TAG and in glycogen accumulation under lipid storage conditions. Overexpression of atf1 and atf2 genes in strain PD630 promoted an increase of approximately 10 % (w/w) in TAG accumulation, while heterologous expression of atf2 gene in Mycobacterium smegmatis caused an increase in TAG accumulation during cultivation in nitrogen-rich media. This study demonstrated that, in addition to atf1 gene, atf2 is actively involved in TAG accumulation by the oleaginous R. opacus PD630.