Marine bacteria acquire the essential nutrient phosphorus using a novel bond
A group of early career researchers from the Department of Molecular Biology and Biotechnology at the University of Sheffield has published work in the journal Nature Communications (DOI:10.1038/s41467-017-01226-8). Their research, in collaboration with colleagues at the University of Southampton, describes how marine and soil bacteria use a specific interaction to scavenge the vital element phosphorus from their environment.
Phosphorus is essential for life. It is a crucial component of DNA, important for the structure of cells, and vital for metabolism. Phosphorus based fertilizers are essential for agriculture and livestock farming, and in turn for food production and security.
In nature, phosphorus is mainly found as an inorganic ion called phosphate. In most natural environments the availability of phosphate is typically very low and can prevent the growth of microorganisms. This is often the case in the nutrient poor oceans, and marine microorganisms that live in seawater have evolved ways to acquire and utilise alternative forms of phosphorus in order to survive under phosphate depleted conditions. Two such alternative sources of phosphorus are phosphite and hypophosphite. Dr Andrew Hitchcock, one of the scientists involved in the research, said “Phosphite, in particular, is emerging as a potentially important component of the marine phosphorus cycle. The concentration of these compounds in the oceans is currently unknown, but some marine bacteria are able to utilise them as a source of phosphorus and we wanted to find out how they are able to acquire them.”
Some bacteria make proteins that selectively bind phosphite or hypophosphite with high affinity, allowing the organisms to scavenge them from the environment, where they are likely to be present in very low amounts. Once inside the bacteria the compounds are converted to phosphate, which can be used directly by the cell.
The authors of the study determined the 3-dimensional structure of some of these proteins using a technique called X-ray crystallography. Their results reveal that the proteins use a P-H…Pi interaction to bind phosphite or hypophosphite, where the phosphorus-hydrogen (P-H) is positioned next to a specific aromatic amino acid in the core of the protein. Aromatic amino acids have a ring type structure, allowing them to form this type of interaction. Dr Claudine Bisson said “We believe this is the first example of a P-H…Pi bond between a protein and its ligand, and explains the high affinity and selectivity of these transporters for phosphite and hypophosphite”.
Dr Nate Adams added “The characterisation of these transporters may also be useful for biotechnological and agricultural applications, where phosphite is used both as a source of phosphorus and as an alternative to selection using antibiotic resistance markers”.
The research paper, The molecular basis of phosphite and hypophosphite recognition by ABC transporters, is published on the Nature Communications website.