Molecular cloning, mapping, and regulation of Pho regulon genes for phosphonate breakdown by the phosphonatase pathway of Salmonella typhimurium LT2

Abstract

Two pathways exist for cleavage of the carbon-phosphorus (C-P) bond of phosphonates, the C-P lyase and the phosphonatase pathways. It was previously demonstrated that Escherichia coli carries genes (named phn) only for the C-P lyase pathway and that Enterobacter aerogenes carries genes for both pathways (K.-S. Lee, W. W. Metcalf, and B. L. Wanner, J. Bacteriol. 174:2501-2510, 1992). In contrast, here it is shown that Salmonella typhimurium LT2 carries genes only for the phosphonatase pathway. Genes for the S. typhimurium phosphonatase pathway were cloned by complementation of E. coli ⌬phn mutants. Genes for these pathways were proven not to be homologous and to lie in different chromosomal regions. The S. typhimurium phn locus lies near 10 min; the E. coli phn locus lies near 93 min. The S. typhimurium phn gene cluster is about 7.2 kb in length and, on the basis of gene fusion analysis, appears to consist of two (or more) genes or operons that are divergently transcribed. Like that of the E. coli phn locus, the expression of the S. typhimurium phn locus is activated under conditions of P i limitation and is subject to Pho regulon control. This was shown both by complementation of the appropriate E. coli mutants and by the construction of S. typhimurium mutants with lesions in the phoB and pst loci, which are required for activation and inhibition of Pho regulon gene expression, respectively. Complementation studies indicate that the S. typhimurium phn locus probably includes genes both for phosphonate transport and for catalysis of C-P bond cleavage.Phosphonates (Pn) are a large class of molecules containing a direct carbon-phosphorus (C-P) bond in place of the more familiar carbon-oxygen-phosphorus bond of phosphoesters. Although Pn do not exist in all organisms, they do exist in many different ones. Pn have been found in organisms as diverse as the intracellular procaryote Bdellovibrio species, the filamentous bacteria streptomycetes, the protozoans Tetrahymena and Trypanosoma spp., mollusks, insects, and others. In these organisms, Pn have been isolated as constituents of glycolipids, glycoproteins, polysaccharides, or phosphonolipids. In Bacteroides fragilis, Pn were identified as components of capsular polysaccharide (6); in streptomycetes, Pn are synthesized as antibiotics such as fosfomycin (25); in Tetrahymena spp., Pn exist as phosphonolipids (19); in Trypanosoma cruzi, Pn are components of lipopeptidophosphoglycan (the major cell surface glycoconjugate [10]); in a sea anemone, Pn are the major P compounds (38); and in a locus, a Pn is the principal P compound of hemolymph (20). Yet, in spite of their widespread natural occurrence, the biological role of natural Pn is poorly understood (17). In phosphonolipids, 2-aminoethylphosphonate (AEPn) exists in place of its analog ethanolamine phosphate.No doubt because of the abundance of PN in nature, bacteria have acquired pathways for Pn breakdown. Bacteria capable of breaking the C-P bond may use Pn as a sole P source, for which two pathways exist, the C-P l...

Comparative genomic, proteomic and exoproteomic analyses of three Pseudomonas strains reveals novel insights into the phosphorus scavenging capabilities of soil bacteria

“…Based on our data, we cannot rule out the possibility that DSM4166 can also grow on phosphonates as a source of P for two reasons: (i) Although phosphonate degradation has been well documented in recent years (Jiang et al ., 1995; White and Metcalf, 2007; Villarreal‐Chiu et al ., 2012; McGrath et al ., 2013), bacteria capable of growing on phosphonates that do not possess any of the characterized genes/proteins have been isolated, demonstrating alternative pathways for phosphonate degradation must exist in nature (Fox and Mendz, 2006); (ii) DSM4166 possesses and expressed a number of putative phosphonate transporters (Table 1 and Fig. 6).…”

Alternative pathways for phosphonate metabolism in thermophilic cyanobacteria from microbial mats

“…In Salmonella sp. Phnase is induced under P starvation (Jiang et al, 1995) but in Rhizobium huakuii PMY1, Phnase are not under control of the Pho regulon. The ability of Syn OS-A to induce specific Phnases, in the presence of P, might indicate that Phns are available in these environments.…”

Mapping of orthologous genes in the context of biological pathways: An application of integer programming

“…This organism also has P i -transport systems and a two-component regulatory system, although it has only one low-affinity P i transporter, pitA (37). Moreover, it uses only one special form of P n , 2-aminoethylphosphonate (2-AEP), which is transported by phnSTUV and broken down by phnW and phnX (31,32). In addition, the porin phoE, located in the outer membrane, is regulated by phoB also.…”

“…We now present a prediction of the phosphorus-assimilation pathway in Synechococcus sp. WH8102 (WH8102) through mapping pathway models from four other organisms: B. subtilis (15), E. coli K12 (26)(27)(28)(29)(30), Salmonella typhimurium (31,32), and Synecocystis PCC 6803 (33). Before our work, very little was known about this particular pathway in this species, although some general knowledge about the phosphorus-assimilation process has been documented (34).…”