Phosphorus (P) is an essential nutrient required for life. In the ocean, dissolved organic phosphorus (DOP) supports the growth and productivity of marine microbes across different ocean ecosystems. To satisfy their nutritional P requirement, marine microorganisms produce an array of metal-dependent P hydrolases, such as alkaline phosphatases (APs), to acquire orthophosphate (Pi) from different DOP compounds, including P-esters, P-anhydrides, and phosphonates. However, the biochemical basis of most DOP transformations, their contributions to microbial P demand, and their role within the marine biogeochemical P cycle remain poorly understood. Here, we report crucial insights into the metal-dependent hydrolysis and utilization of different DOP substrates by marine plankton at the molecular, species and community levels. Proteomic analyses for diatoms of the genus Thalassiosira spp. implicated the involvement of unexpected hydrolases instead of APs in the preferential degradation of extracellular P-anhydrides over other DOP classes. To verify this, an inorganic metallo-pyrophosphatase (PPase1335; NCBI EED90627) detected in the exoproteome of from T. pseudonana CMP1335 was recombinantly expressed in Escherichia coli, purified, and tested for activity toward different DOP compounds as a function of metal composition. Indeed, PPase1335 in the presence of magnesium or manganese is able to rapidly and fully convert the P-anhydride 3-poly-P to Pi, whereas addition of cobalt enables P-monoester hydrolysis. In order to probe for potential metal regulation of DOP cycling in the marine environment, field incubations were conducted at the Scripps Pier and during a cruise in the California Current Ecosystem (CCE). Seawater from both sampling sites was incubated with and without the addition of different metals, and metal-dependent DOP hydrolysis rates were assessed after 48h. While generally higher in the CCE, bulk P hydrolase activity increased drastically in the iron and zinc-amended samples at both stations, indicating potential metal limitation of DOP remineralization. These new findings are especially important given that the CCE was previously characterized with transient iron and phosphate scarcity. Altogether, this work provides essential molecular- and community-scale verification of compound-specific and metal-dependent DOP biotransformations, and creates new knowledge of intertwined metal and P cycling within marine microbial communities.

Metalloenzyme-driven transformations within the marine microbial phosphorus cycle

ACS Fall 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.