Project description:The toxic arsenate ion can behave as a phosphate analog, and this can result in arsenate toxicity especially in areas with elevated arsenate to phosphate ratios like the surface waters of the ocean gyres. In these systems, cellular arsenate resistance strategies would allow phytoplankton to ameliorate the effects of arsenate transport into the cell. Despite the potential coupling between arsenate and phosphate cycling in oligotrophic marine waters, relatively little is known about arsenate resistance in the nitrogen-fixing marine cyanobacteria that are key components of the microbial community in low nutrient systems. The unicellular diazotroph, Crocosphaera watsonii WH8501, was able to grow at reduced rates with arsenate additions up to 30 nM, and estimated arsenate to phosphate ratios of 6:1. The genome of strain WH8501 contains homologs for arsA, arsH, arsB, and arsC, allowing for the reduction of arsenate to arsenite and the pumping of arsenite out of the cell. The short-term addition of arsenate to the growth medium had no effect on nitrogen fixation. However, arsenate addition did result in the up-regulation of the arsB gene with increasing arsenate concentrations, indicating the induction of the arsenate detoxification response. The arsB gene was also up-regulated by phosphorus stress in concert with a gene encoding the high-affinity phosphate binding protein pstS. Both genes were down-regulated when phosphate was re-fed to phosphorus-stressed cells. A field survey of surface water from the low phosphate western North Atlantic detected expression of C. watsoniiarsB, suggestive of the potential importance of arsenate resistance strategies in this and perhaps other systems.

| S-EPMC3201022 | biostudies-literature

Phosphorus scavenging in the unicellular marine diazotroph Crocosphaera watsonii.

Project description:Through the fixation of atmospheric nitrogen and photosynthesis, marine diazotrophs play a critical role in the global cycling of nitrogen and carbon. Crocosphaera watsonii is a recently described unicellular diazotroph that may significantly contribute to marine nitrogen fixation in tropical environments. One of the many factors that can constrain the growth and nitrogen fixation rates of marine diazotrophs is phosphorus bioavailability. Using genomic and physiological approaches, we examined phosphorus scavenging mechanisms in strains of C. watsonii from both the Atlantic and the Pacific. Observations from the C. watsonii WH8501 genome suggest that this organism has the capacity for high-affinity phosphate transport (e.g., homologs of pstSCAB) in low-phosphate, oligotrophic systems. The pstS gene (high-affinity phosphate binding) is present in strains isolated from both the Atlantic and the Pacific, and its expression was regulated by the exogenous phosphate supply in strain WH8501. Genomic observation also indicated a broad capacity for phosphomonoester hydrolysis (e.g., a putative alkaline phosphatase). In contrast, no clear homologs of genes for phosphonate transport and hydrolysis could be identified. Consistent with these genomic observations, C. watsonii WH8501 is able to grow on phosphomonoesters as a sole source of added phosphorus but not on the phosphonates tested to date. Taken together these data suggest that C. watsonii has a robust capacity for scavenging phosphorus in oligotrophic systems, although this capacity differs from that of other marine cyanobacterial genera, such as Synechococcus, Prochlorococcus, and Trichodesmium.

| S-EPMC1392970 | biostudies-literature

Crocosphaera subtropica

Project description:Crocosphaera subtropica overview

| PRJNA1215469 | ENA

Crocosphaera watsonii

Project description:Nitrogen-fixing cyanobacterium

| PRJNA35299 | ENA