The molecular basis of phosphite and hypophosphite recognition by ABC-transporters

Abstract

Inorganic phosphate is the major bioavailable form of the essential nutrient phosphorus. However, the concentration of phosphate in most natural habitats is low enough to limit microbial growth. Under phosphate-depleted conditions some bacteria utilise phosphite and hypophosphite as alternative sources of phosphorus, but the molecular basis of reduced phosphorus acquisition from the environment is not fully understood. Here, we present crystal structures and ligand binding affinities of periplasmic binding proteins from bacterial phosphite and hypophosphite ATP-binding cassette transporters. We reveal that phosphite and hypophosphite specificity results from a combination of steric selection and the presence of a P-H…π interaction between the ligand and a conserved aromatic residue in the ligand-binding pocket. The characterisation of high affinity and specific transporters has implications for the marine phosphorus redox cycle, and might aid the use of phosphite as an alternative phosphorus source in biotechnological, industrial and agricultural applications.

Metabolic engineering of phosphite metabolism in Synechococcus elongatus PCC 7942 as an effective measure to control biological contaminants in outdoor raceway ponds

“…Motomura et al [21], reported the use of 0.2 mM Phi in their experiments, in which the WT strain displayed slight growth. The engineered strains, harboring both the ptxD gene and the Phi-transporter genes, showed also a reduced growth using Phi compared to the WT using Pi, which was attributed to the type of transporter they expressed (HtxBCDE), that has an extremely low a nity for phosphite (K d > 10 mM) [33].…”

“…The mechanism of transport and metabolism of Phi have been widely studied in P. stutzeri WM88, in which Phi is taken up via the PtxABC transporter and then oxidized into Pi by the PtxD oxidoreductase [33,34]. Some reports suggest that certain marine cyanobacteria are able to take up and metabolize Phi as P source and Phi metabolism-related genes may be widely present in marine environments [26,35,36].…”

Growth and selection of the cyanobacterium Synechococcus sp. PCC 7002 using alternative nitrogen and phosphorus sources

“…Putative phosphonate transporter genes were identified by using the BlastP tool within CyanoBase (http://genome.microbedb.jp/blast/blast_search/cyanobase/genes), limiting the search to Syn7002 and using as a search template the amino acid sequence of PhnD from Prochlorococcus marinus 11 sp. MIT9301 (Bisson et al, 2017;Feingersch et al, 2012). Two homologues (annotated as putative phosphate/phosphonate-binding ABC transporters) were identified in Syn7002: A0336 (E value = 1e -96 ) and G0143 (E value = 2e -08 ).…”

“…However, Phi uptake in Syn7002, unlike A. thaliana, is much less efficient. As previous studies have shown that several marine cyanobacteria are able to take up and utilize Phi as a phosphorus source (Feingersch et al, 2012;Martinez et al, 2012;Polyviou et al, 2015) we searched the Syn7002 genome for putative transporter genes, such as ptxB and phnD homologues (Bisson et al, 2017). While no ptxB homologues could be found, two putative phnD genes, A0336 and G0143, were present in either the circular chromosome (A0336) or the pAQ7 plasmid (G0143) (see Suppl.…”

“…5). We hypothesized that either of these two genes might be involved in phosphite import to the cell, as phnD homologues were shown to also bind phosphite (Bisson et al, 2017). However, knock-out of these putative phosphonate transporters, either alone or in combination, did not result in an inability of the ptxD parental strain to grow on phosphite (Suppl.…”