Involvement of the Escherichia coli phn (psiD) gene cluster in assimilation of phosphorus in the form of phosphonates, phosphite, Pi esters, and Pi

Abstract

The phn (psiD) gene cluster is induced during Pi limitation and is required for the use of phosphonates (Pn) as a phosphorus (P) source. Twelve independent Pn-negative (Pn-) mutants have lesions in the phn gene cluster which, as determined on the basis of recombination frequencies, is larger than 10 kbp. This distance formed the basis for determining the complete DNA sequence of a 15.6-kbp BamHI Interestingly, all Pn-mutations abolish the use not only of Pn but also of Pt, in which P is in the +3 oxidation state. Therefore, Pn metabolism and Pt metabolism are related, supporting a biochemical mechanism for carbon-phosphorus bond cleavage which involves redox chemistry at the P center. Furthermore, our discovery of Pi-regulated genes for the assimilation of reduced P suggests that a P redox cycle may be important in biology.Living systems satisfy their need for phosphorus (P) primarily through Pi, in which P is in its highest, +5, oxidation state. Pi enters Escherichia coli via the low-affinity P1 transporter (Pit) when present in excess or via the high-affinity phosphate-specific transporter (Pst) when present in low levels (<4 x 10-6 M). The low-affinity Pi transporter is a single-component system, analogous to LacY, which is made constitutively (41). In contrast, Pst is a multicomponent periplasmic binding protein-dependent system (16) encoded by the pstSCAB-phoU operon, the expression of which is highly regulated. The pstS promoter is expressed at a low, basal level when P1 is present in excess; it shows 100-fold derepression during Pi-limited growth (unpublished data The phosphate regulon (PHO regulon) consists of several P1 starvation-inducible (psi) genes, the products of which act primarily in the assimilation of environmental P (52). The PHO regulon includes (i) the phoBR operon, which encodes * Corresponding author. the environmental Pi sensor, PhoR, and the PHO regulon activator, PhoB (29, 30); (ii) the aforementioned pstSCABphoU operon; (iii) the phoA operon (34), which encodes bacterial alkaline phosphatase (Bap), a nonspecific phosphomonoesterase; (iv) the phoE gene, which encodes an outer membrane porin selective for polyanions (5)

Potential for phosphite and phosphonate utilization by Prochlorococcus

“…It is important to note that using ITC measurements, we failed to detect any binding of the E. coli PhnD protein either to phosphite or to phosphate. These were previously suggested to be P substrates in E. coli (Metcalf and Wanner, 1991;Rizk et al, 2006)). Interestingly, both Prochlorococcus PhnD proteins showed a completely different specificity range: one (PhnD2) binds strongly only to MPn, EPn and inorganic phosphite, whereas the other (PhnD1) binds strongly to inorganic phosphite and with very weak affinities to MPn and phosphate (see Table S1 for dissociation constants).…”

Metagenomic analysis of two enhanced biological phosphorus removal (EBPR) sludge communities

“…A promoter similar to the pho box encountered in E. coli 41 TCAAGC, which is very similar to the pho box reported in E. coli 41 . This system is known to strongly regulate the expression of Pst, derepressing it only in cases of low Pi concentrations 40,42 . Therefore, it is likely that the Pst system is repressed for most of the EBPR cycle, with the possible exception of the end of the aerobic period when Pi concentrations drop to uM levels.…”

Methane production by phosphate-starved SAR11 chemoheterotrophic marine bacteria

“…and other heterotrophic bacteria 10,12 , as well as marine autotrophs such as Trichodesmium 19 , have been shown to use MPn as a sole P source. In these organisms, MPn degradation proceeds via the C-P lyase pathway and is induced by P i starvation 12,[20][21][22][23] . Building on these findings, studies by Karl et al 9 and Martínez et al 17 showed that when surface seawater is amended with glucose and a nitrogen source (to stimulate P i -limiting conditions), MPn hydrolysis and CH 4 production proceeds at rates that scale inversely with the addition of exogenous P i .…”

“…strain HTCC7211 (str. HTCC7211), isolated from the North Atlantic Ocean in the Sargasso Sea 32 , encodes for additional proteins involved in organophosphorus transport (PhnCDEE 2 ) 20 and phosphonate utilization (PhnGHIJKLNM), suggesting that the two organisms have evolved different adaptive strategies for P acquisition related to niche partitioning 14 .…”