Intriguingly, we observed that the CFU/ml/ABS600 values for the four strains used in our studies diverged dramatically following mid-stationary phase (Figure 2D). We consistently found that hfq∆/empty see more vector cultures experienced a precipitous drop in CFU counts late in stationary phase. In most cases, culturable cell counts had dropped to zero CFU/ml by 30 hours. In contrast, MR-1/empty

vector cultures were much more robust than hfq∆ /empty vector cultures, maintaining significant CFU counts, even after 30 hours of growth. The data presented in Figure 2D represents a typical result for an iteration of this experiment. It is worth noting, however, that the timing of the beginning of the reduction in CFU counts observed for the MR-1/empty vector strain and for the hfq∆/empty vector strain could vary by several hours between independent cultures, even parallel cultures simultaneously inoculated using the same preculture (data not shown). Furthermore,

we also consistently observed that MR-1/phfq and hfq∆/phfq cultures, which contain more Hfq protein than wild type cultures at 24 hours (Figure 1C), retained significantly higher numbers of colony forming units compared to MR-1/empty vector cultures in extended stationary phase. Taken together, our loss-of-function and check details gain-of-function analyses demonstrate that Hfq promotes cell survival or culturability in extended FRAX597 research buy stationary phase. The hfq∆ mutant is impaired in anaerobic growth and chromium reduction To characterize the role of S. oneidensis Chlormezanone hfq in anaerobic growth, we compared the growth kinetics of strains MR-1/empty vector, MR-1/phfq, hfq∆/empty vector, and hfq∆ /phfq grown in modified M1 defined medium with fumarate as the terminal electron acceptor. Similar to the growth defects observed during aerobic growth, anaerobic hfq∆ /empty vector cultures grew more slowly during exponential phase and reached a lower terminal density than MR-1/empty vector cultures. (Figure 3A). The growth and terminal density defects of hfq mutant cultures in anaerobic modified M1 plus fumarate

were completely rescued by phfq, as the growth of the hfq∆/phfq strain was indistinguishable from that of MR-1/empty vector (Figure 3A). Extra copies of hfq did not alter the ability of S. oneidensis to utilize fumarate as a terminal electron acceptor, as growth of MR-1/phfq and hfq∆/phfq cultures was very similar to that of MR-1/empty vector cultures (Figure 3A). Figure 3 The hfq∆ mutant is deficient in anaerobic respiration. (A) Growth of MR-1/empty vector, MR-1/phfq, hfq∆ /empty vector, and hfq∆ /phfq under anaerobic conditions with fumarate as the terminal electron acceptor. Data presented is from three independent cultures. Error bars represent a 99% confidence interval (P = 0.01). (B and C) Results of chromium reduction assays. Chromium reduction/disappearance of Cr(VI) was assayed using the diphenylcarbazide method.