The nosocomial pathogen
Acinetobacter baumannii
acquired clinical significance due to the rapid development of its multi-drug resistant (MDR) phenotype.
A
.
baumannii
strains have the ability to colonize several ecological niches including soil, water, and animals, including humans. They also survive under extremely harsh environmental conditions thriving on rare and recalcitrant carbon compounds. However, the molecular basis behind such extreme adaptability of
A
.
baumannii
is unknown. We have therefore determined the complete genome sequence of
A
.
baumannii
DS002, which was isolated from agricultural soils, and compared it with 78 complete genome sequences of
A
.
baumannii
strains having complete information on the source of their isolation. Interestingly, the genome of
A
.
baumannii
DS002 showed high similarity to the genome of
A
.
baumannii
SDF isolated from the body louse. The environmental and clinical strains, which do not share a monophyletic origin, showed the existence of a strain-specific unique gene pool that supports niche-specific survival. The strains isolated from infected samples contained a genetic repertoire with a unique gene pool coding for iron acquisition machinery, particularly those required for the biosynthesis of acinetobactin. Interestingly, these strains also contained genes required for biofilm formation. However, such gene sets were either partially or completely missing in the environmental isolates, which instead harbored genes required for alternate carbon catabolism and a TonB-dependent transport system involved in the acquisition of iron via siderophores or xenosiderophores.
The complete genome sequence of Brevundimonas diminuta represented a chromosome (∼4.15 Mb) and two plasmids (pCMS1 and pCMS2) with sizes of 65,908 and 30,654 bp, respectively. The sequence of the genome showed no significant similarity with the known bacterial genome sequences, instead showed weak similarity with the members of different genera of family, Sphingomonadaceae. Contradicting existing taxonomic position, the core genome-guided phylogenetic tree placed B. diminuta in the genus Sphingopyxis and showed sufficient genome-to-genome distance warranting a new species name. Reflecting the strains ability to grow in harsh environments, the genome-contained genetic repertoire required for mineralization of several recalcitrant man-made aromatic compounds.
In previous studies, we have shown the existence of metabolic remodeling in glucose-grown Escherichia coli MG1655 cells expressing the esterase Orf306 from the opd island of Sphingobium fuliginis. We now show that Orf306-dependent metabolic remodeling is due to regulation of a novel small RNA (sRNA). Endogenous propionate, produced due to the esterase/lipase activity of Orf306, repressed expression of a novel E. coli sRNA, co293. This sRNA post-transcriptionally regulates expression of the transcription factors HcaR and FadR either by inhibiting translation or by destabilizing their transcripts. Hence, repression of co293 expression elevates the levels of HcaR and FadR with consequent activation of alternative carbon catabolic pathways. HcaR activates the hca and MHP operons leading to upregulation of the phenyl propionate and hydroxy phenyl propionate (HPP) degradation pathways. Similarly, FadR stimulates the expression of the transcription factor IclR which negatively regulates the glyoxylate bypass pathway genes, aceBAK.
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