Changes in relative transcript amounts caused by hydrogen sulfide treatment, deletion of BigR, and BigR mutant complement in Acinetobacter baumannii

Acinetobacter baumannii is an opportunistic nosocomial pathogen that is the causative agent of several serious infections in humans. Here, we investigate the response of A. baumannii toward sodium sulfide (Na2S), known to be associated with some biofilms at oxic/anoxic interfaces, as a model for how this major human pathogen manages sulfide homeostasis. These results reveal that A. baumannii encodes two persulfide-sensing transcriptional regulators, a primary sigma54-dependent transcriptional activator (FisR), and a secondary system controlled by the persulfide-sensing repressor biofilm growth-associated repressor (BigR) both of which regulate operons encoding for sulfide detoxification or transportation. In addition, sulfide induces an alternative cytochrome bd oxidase which is refractory to inhibition by H2S and represses importers of alternate sulfur sources. Lastly, our results suggest additional genes regulated by BigR beyond sulfide detoxification including genes associated with assembly of type 1 chaperone-usher pilus. Overall design: RNA for the sulfide experiment was prepared from cultures of wild-type and ?bigR and ?bigR mTn7(bigRC34A/C100A) strains of Acinetobacter baumannii 17978 grown exponentially in LB media at 37°C to OD600=0.2. At this point Na2S was added to treated cultures at a ?nal concentration of 0.2 mM for a 10 min exposure, then samples were collected from all treated and untreated conditions. Three independent biological replicates of RNA were prepared for each strain or condition. cDNA libraries were sequenced and the sequencing results were used as the data base for differential expression analysis.