hipBA toxin-antitoxin systems mediate persistence in Caulobacter crescentus.

Antibiotic persistence is a transient phenotypic state during which a bacterium can withstand otherwise lethal antibiotic exposure or environmental stresses. In Escherichia coli, persistence is promoted by the HipBA toxin-antitoxin system. The HipA toxin functions as a serine/threonine kinase that inhibits cell growth, while the HipB antitoxin neutralizes the toxin. E. coli HipA inactivates the glutamyl-tRNA synthetase GltX, which inhibits translation and triggers the highly conserved stringent response. Although hipBA operons are widespread in bacterial genomes, it is unknown if this mechanism is conserved in other species. Here we describe the functions of three hipBA modules in the alpha-proteobacterium Caulobacter crescentus. The HipA toxins have different effects on growth and macromolecular syntheses, and they phosphorylate distinct substrates. HipA1 and HipA2 contribute to antibiotic persistence during stationary phase by phosphorylating the aminoacyl-tRNA synthetases GltX and TrpS. The stringent response regulator SpoT is required for HipA-mediated antibiotic persistence, but persister cells can form in the absence of all hipBA operons or spoT, indicating that multiple pathways lead to persister cell formation in C. crescentus.

The nutrient supplying capabilities of Uzinura, an endosymbiont of armoured scale insects.

An emerging common physiological feature of plant sap-feeding insects is the presence of bacterial endosymbionts capable of providing essential nutrients to their host. These microbial partners are inviable outside of specialized host tissues, and therefore a cultivation-independent approach, namely high-throughput next-generation genome sequencing, can be used to characterize their gene content and metabolic potential. To this end, we sequenced the first complete genome of the obligate endosymbiont, Candidatus 'Uzinura diaspidicola', of armoured scale insects. At 263 431 bp, Uzinura has an extremely reduced genome that is composed largely of genes encoding enzymes involved in translation and amino acid biosynthesis. The tiny size of the Uzinura genome parallels that observed in some other insect endosymbionts. Despite this extreme genome reduction, the absence of a known obligate partner bacterial symbiont suggests that Uzinura alone can supply sufficient nutrients to its host.

Genome sequence of Blattabacterium sp. strain BGIGA, endosymbiont of the Blaberus giganteus cockroach.

Cockroaches harbor the obligate flavobacterial endosymbiont Blattabacterium sp., which resides within the host's bacteriocytes and can recycle ammonia and urea nitrogenous wastes into amino acids for the host. We report the complete genome sequence of the Blattabacterium sp. associated with the giant roach Blaberus giganteus.