Bacterial fatty acid synthesis (FASII) is an attractive target for treatment of Gram‐positive pathogens. The value of FASII inhibitors was recently questioned based on the ability of Streptococcus agalactiae to circumvent inhibition by utilizing exogenous fatty acids (FA) for phospholipid synthesis. This study compares the efficacy of FASII inhibitors against Staphylococcus aureus and Streptococcus pneumoniae grown in media containing FA. Exogenous FA overcame inhibition in S. pneumoniae, but not S. aureus. Neither the substrate specificities of the acyltransferases, nor the divergent modes of transcriptional regulation accounted for this difference. Exogenous FA strongly suppressed malonyl‐CoA production in S. pneumoniae but not S. aureus, indicating biochemical regulation at the acetyl‐CoA carboxylase in S. pneumoniae is the key difference between the two species. The lack of feedback regulation of malonyl‐CoA formation results in the accumulation of short chain acyl‐ACP and a block in exogenous FA uptake in S. aureus treated with FASII inhibitors. The ability of exogenous FA to biochemically inhibit the initiation of FASII determines whether FASII inhibitors will be effective against Gram‐Positive bacteria in the presence of exogenous FA. Supported by NIH GM034496 and ALSAC.

Agrobacterium tumefaciens is capable of transferring and integrating an oncogenic T-DNA (transferred DNA) from its tumor-inducing (Ti) plasmid into dicotyledonous plants. This transfer requires that the virulence genes (vir regulon) be induced by plant signals such as acetosyringone in an acidic environment. Salicylic acid (SA) is a key signal molecule in regulating plant defense against pathogens. However, how SA influences Agrobacterium and its interactions with plants is poorly understood. Here we show that SA can directly shut down the expression of the vir regulon. SA specifically inhibited the expression of the Agrobacterium virA/G two-component regulatory system that tightly controls the expression of the vir regulon including the repABC operon on the Ti plasmid. We provide evidence suggesting that SA attenuates the function of the VirA kinase domain. Independent of its effect on the vir regulon, SA up-regulated the attKLM operon, which functions in degrading the bacterial quormone N-acylhomoserine lactone. Plants defective in SA accumulation were more susceptible to Agrobacterium infection, whereas plants overproducing SA were relatively recalcitrant to tumor formation. Our results illustrate that SA, besides its well known function in regulating plant defense, can also interfere directly with several aspects of the Agrobacterium infection process.two-component system ͉ tumorigenesis ͉ defense response ͉ rhizosphere ͉ plant-microbe interaction

Agrobacterium tumefaciens transferred DNA (T-DNA) transfer requires that the virulence genes (vir regulon) on the tumor-inducing (Ti) plasmid be induced by plant phenolic signals in an acidic environment. Using transcriptome analysis, we found that these acidic conditions elicit two distinct responses: (i) a general and conserved response through which Agrobacterium modulates gene expression patterns to adapt to environmental acidification and (ii) a highly specialized acid-mediated signaling response involved in Agrobacterium-plant interactions. Overall, 78 genes were induced and 74 genes were repressed significantly under acidic conditions (pH 5.5) compared to neutral conditions (pH 7.0). Microarray analysis not only confirmed previously identified acid-inducible genes but also uncovered many new acid-induced genes which may be directly involved in Agrobacterium-plant interactions. These genes include virE0, virE1, virH1, and virH2. Further, the chvG-chvI two-component system, previously shown to be critical for virulence, was also induced under acid conditions. Interestingly, acidic conditions induced a type VI secretion system and a putative nonheme catalase. We provide evidence suggesting that acid-induced gene expression was independent of the VirA-VirG two-component system. Our results, together with previous data, support the hypothesis that there is three-step sequential activation of the vir regulon. This process involves a cascade regulation and hierarchical signaling pathway featuring initial direct activation of the VirA-VirG system by the acid-activated ChvG-ChvI system. Our data strengthen the notion that Agrobacterium has evolved a mechanism to perceive and subvert the acidic conditions of the rhizosphere to an important signal that initiates and directs the early virulence program, culminating in T-DNA transfer.

Agrobacterium tumefaciens possesses three iron-containing superoxide dismutases (FeSods) encoded by distinct genes with differential expression patterns. SodBI and SodBII are cytoplasmic isozymes, while SodBIII is a periplasmic isozyme. sodBI is expressed at a high levels throughout all growth phases. sodBII expression is highly induced upon exposure to superoxide anions in a SoxR-dependent manner. sodBIII is expressed only during stationary phase. Analysis of the physiological function of sods reveals that the inactivation of sodBI markedly reduced levels of resistance to a superoxide generator, menadione. A mutant lacking all three Sod enzymes is the most sensitive to menadione treatment, indicating that all sods contribute at various levels towards the overall menadione resistance level. Sods also have important roles in A. tumefaciens virulence toward a host plant. A sodBI but not a sodBII or sodBIII mutant showed marked reduction in its ability to induce tumors on tobacco leaf discs, while the triple sod null mutant is avirulent.

eWe have thoroughly investigated the abrB2 gene (sll0822) encoding an AbrB-like regulator in the wild-type strain of the model cyanobacterium Synechocystis strain PCC6803. We report that abrB2 is expressed from an active but atypical promoter that possesses an extended ؊10 element (TGTAATAT) that compensates for the absence of a ؊35 box. Strengthening the biological significance of these data, we found that the occurrence of an extended ؊10 promoter box and the absence of a ؊35 element are two well-conserved features in abrB2 genes from other cyanobacteria. We also show that AbrB2 is an autorepressor that is dispensable to cell growth under standard laboratory conditions. Furthermore, we demonstrate that AbrB2 also represses the hox operon, which encodes the Ni-Fe hydrogenase of biotechnological interest, and that the hox operon is weakly expressed even though it possesses the two sequences resembling canonical ؊10 and ؊35 promoter boxes. In both the AbrB2-repressed promoters of the abrB2 gene and the hox operon, we found a repeated DNA motif [TT-(N 5 )-AAC], which could be involved in AbrB2 repression. Supporting this hypothesis, we found that a TT-to-GG mutation of one of these elements increased the activity of the abrB2 promoter. We think that our abrB2-deleted mutant with increased expression of the hox operon and hydrogenase activity, together with the reporter plasmids we constructed to analyze the abrB2 gene and the hox operon, will serve as useful tools to decipher the function and the regulation of hydrogen production in Synechocystis. C yanobacteria are ancient photoautotrophic prokaryotes that are regarded as the progenitors of oxygenic photosynthesis (33, 39) and the plant chloroplast (8). Over time, cyanobacteria have evolved as the largest and most diverse groups of bacteria (44) and have colonized most waters and soils of our planet. The hardiness of cyanobacteria is due to their efficient photosynthesis, which uses nature's most abundant resources, solar energy, water, CO 2 , and mineral nutrients, to produce a large part of the atmospheric oxygen and organic assimilates for the food chain (52). On a global scale, cyanobacteria fix an estimated 25 gigatons of carbon from CO 2 per year into energy-dense biomass (37, 49). To perform this huge CO 2 fixation, cyanobacteria use 0.2 to 0.3% (49) of the total solar energy, 178,000 TW, reaching the Earth's surface (22). Thus, the amount of energy passing through cyanobacteria exceeds by more than 25 times the energy demand of human society (about 15 TW), roughly 1,000 times the total nuclear energy produced on Earth.