Marine picocyanobacterial PhnD1 shows specificity for various phosphorus sources but likely represents a constitutive inorganic phosphate transporter

Bhumika S. Shah*, Benjamin A. Ford, Deepa Varkey, Halina Mikolajek, Christian Orr, Vitaliy Mykhaylyk, Raymond J. Owens, Ian T. Paulsen*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)
39 Downloads (Pure)


Despite being fundamental to multiple biological processes, phosphorus (P) availability in marine environments is often growth-limiting, with generally low surface concentrations. Picocyanobacteria strains encode a putative ABC-type phosphite/phosphate/phosphonate transporter, phnDCE, thought to provide access to an alternative phosphorus pool. This, however, is paradoxical given most picocyanobacterial strains lack known phosphite degradation or carbon-phosphate lyase pathway to utilise alternate phosphorus pools. To understand the function of the PhnDCE transport system and its ecological consequences, we characterised the PhnD1 binding proteins from four distinct marine Synechococcus isolates (CC9311, CC9605, MITS9220, and WH8102). We show the Synechococcus PhnD1 proteins selectively bind phosphorus compounds with a stronger affinity for phosphite than for phosphate or methyl phosphonate. However, based on our comprehensive ligand screening and growth experiments showing Synechococcus strains WH8102 and MITS9220 cannot utilise phosphite or methylphosphonate as a sole phosphorus source, we hypothesise that the picocyanobacterial PhnDCE transporter is a constitutively expressed, medium-affinity phosphate transporter, and the measured affinity of PhnD1 to phosphite or methyl phosphonate is fortuitous. Our MITS9220_PhnD1 structure explains the comparatively lower affinity of picocyanobacterial PhnD1 for phosphate, resulting from a more limited H-bond network. We propose two possible physiological roles for PhnD1. First, it could function in phospholipid recycling, working together with the predicted phospholipase, TesA, and alkaline phosphatase. Second, by having multiple transporters for P (PhnDCE and Pst), picocyanobacteria could balance the need for rapid transport during transient episodes of higher P availability in the environment, with the need for efficient P utilisation in typical phosphate-deplete conditions.

Original languageEnglish
Pages (from-to)1040-1051
Number of pages12
JournalISME Journal
Issue number7
Early online date22 Apr 2023
Publication statusPublished - Jul 2023

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Copyright the Author(s) 2023. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.


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