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. Error bars represent a 99% confidence interval (P = 0.01). (D) Quantification of the rate of Cr(VI) reduction (expressed as the change in ABS541 per minute per ABS600) in the cultures tracked in (C) above during the first five minutes following the addition of chromium to anaerobic cultures. Error bars represent the standard deviation for triplicate cultures. ** indicates that the hfq∆ /empty vector rate is statistically different from the other three strains (P < 0.002 for all three comparison in unpaired two-tailed Student’s T-tests).