Biotin synthesis in Escherichia coli requires the functions of the bioH and bioC genes to synthesize the precursor pimelate moiety by use of a modified fatty acid biosynthesis pathway. However, it was previously noted that bioH has been replaced with bioG or bioK within the biotin synthetic gene clusters of other bacteria. We report that each of four BioG proteins from diverse bacteria and two cyanobacterial BioK proteins functionally replace E. coli BioH in vivo. Moreover, purified BioG proteins have esterase activity against pimeloyl-ACP methyl ester, the physiological substrate of BioH. Two of the BioG proteins block biotin synthesis when highly expressed and these toxic proteins were shown to have more promiscuous substrate specificities than the non-toxic BioG proteins. A postulated BioG-BioC fusion protein was shown to functionally replace both the BioH and BioC functions of E. coli. Although the BioH, BioG and BioK esterases catalyze a common reaction, the proteins are evolutionarily distinct.

Acinetobacter baumannii is found in terrestrial environments but can cause nosocomial infections in very sick patients. A factor that contributes to the prevalence of A. baumannii in hospital settings is that it is intrinsically resistant to dry conditions.

Hospital environments serve as excellent reservoirs for the opportunistic pathogen Acinetobacter baumannii in part because it is exceptionally tolerant to desiccation. To understand the functional basis this trait, we used transposon sequencing (Tn-seq) to identify genes contributing to desiccation tolerance in A. baumannii strain AB5075. We identified 142 candidate desiccation tolerance genes, one of which encoded the global post-transcriptional regulator CsrA. We characterized CsrA in more detail by using proteomics to identify proteins that were differentially present in wild type and csrA mutant cells. Among these were a predicted universal stress protein A, an iron-containing redox protein, a KGG-domain containing protein, and catalase. Subsequent mutant analysis showed that each of these proteins was required for A. baumannii desiccation tolerance. The amino acid sequence of the KGG-domain containing protein predicts that it is an intrinsically disordered protein. Such proteins are critical for desiccation tolerance of the small animals called tardigrades. This protein also has a repeat nucleic acid binding amino acid motif, suggesting that it may protect A. baumannii DNA from desiccation-induced damage.