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Phosphate diester utilization by marine diazotrophs Trichodesmium erythraeum and Crocosphaera watsonii

Tamaha Yamaguchi*, Mitsuhide Sato, Natsuki Gonda, Kazutaka Takahashi, Ken Furuya

*Corresponding author:

ABSTRACT: In the phosphate-depleted oligotrophic ocean, microbes utilize various dissolved organic phosphorus compounds as alternative phosphorus (P) sources, using enzymes such as alkaline phosphatases. However, knowledge of such P acquisition mechanisms is limited, especially in association with the physiology of nitrogen-fixing organisms, which play a substantial role in the marine biogeochemical cycling. We show that the nonaxenic clonal cultures of two oceanic diazotrophs, Trichodesmium erythraeum and Crocosphaera watsonii, have the ability to utilize phosphate diester as their sole P source, using a model artificial compound—bis-p-nitrophenyl phosphate (bisNPP). Although both diazotroph cultures likely preferred phosphate monoester to diester, the expressed diesterase activity was theoretically sufficient to fulfill their P demands, and they showed significant growth in bisNPP-added media. Interestingly, a distinct difference in their growth trends was observed therein, with faster onset of growth by C. watsonii and delayed onset of growth by T. erythraeum. This indicates that the C. watsonii consortium can effectively and rapidly assimilate in situ diesters as alternative P sources in the field. Nonetheless, when considering the poor bisNPP utilization reported from other marine phytoplankton taxa, our results indicate that the utilization of particular diester compounds is a notable and an advantageous strategy for both diazotroph consortia to alleviate P limitation in the oligotrophic ocean.