Chromobacterium violaceum adaptation to low-phosphate conditions
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ORIGINAL PAPER
Chromobacterium violaceum adaptation to low‑phosphate conditions Fernanda Nogales da Costa Vasconcelos1 · Gabriel Padilla1 · Beny Spira1
Received: 21 September 2015 / Revised: 21 December 2015 / Accepted: 8 January 2016 © Springer-Verlag Berlin Heidelberg 2016
Abstract Chromobacterium violaceum is a free-living bacterium that inhabits low-nutrient environments such as the Amazon basin. Bacteria respond to phosphate (Pi) shortage by expressing a range of genes involved in Pi uptake and assimilation, known as the PHO regulon. Several PHO regulon genes have been annotated in the genome of C. violaceum. Here we show that C. violaceum is extremely well adapted to low-Pi conditions. Remarkably, this bacterium is able to grow in media containing only traces of Pi. The PHO regulon genes are induced upon Pi depletion, but the bacteria continued to grow under these conditions. Unlike other Proteobacteria hitherto analyzed, neither PstS nor PhoU play a role in the repression of the PHO regulon under Pi excess. Keywords Chromobacterium violaceum · PHO regulon · pst operon · Phosphate · Nutritional stress
Introduction Free-living organisms frequently face shortage of macronutrients in natural environments, which are often poor in
Communicated by Erko Stackebrandt. Electronic supplementary material The online version of this article (doi:10.1007/s00203-016-1188-6) contains supplementary material, which is available to authorized users. * Beny Spira [email protected] 1
Departamento de Microbiologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, Av. Prof. Lineu Prestes, 1374, São Paulo, SP CEP:05508‑900, Brazil
basic resources, such as carbon, nitrogen and phosphorus (Smil 2000). Phosphorus occurs in nature in its maximal oxidized state (PO43− or Pi), which is also the preferred phosphorus source. Once Pi is taken up by bacteria, it is directly incorporated into phosphorylated monomers, primarily as ATP (Wanner and Wilmes-Riesenberg 1992). Given the importance of Pi and the irregular availability of this nutrient in natural habitats, bacteria must be able to sense changes in Pi concentration in the environment and to modify the pattern of gene expression accordingly. When the external concentration of Pi is below a minimum threshold that supports bacterial growth (ca. 4 μM), a set of genes involved in scavenging alternative sources of this nutrient, the PHO regulon, is activated (Wanner F1996). The most well-studied PHO genes are phoA, the pst operon and the phoBR operon that, respectively, encode the periplasmic enzyme alkaline phosphatase, the high-affinity Pitransport system Pst and the two-component system that controls PHO expression. The histidine kinase PhoR autophosphorylates in response to low Pi in the medium and transfers the Pi moiety to PhoB, which in turn binds to the PHO-boxes, that are specific sequences in the regulatory regions of all PHO genes in place of the standard −35 sequence. PhoB then interacts with the RNA polymerase associated with σ70, thus initiating transcriptio
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