Depth distributions of alkaline phosphatase and phosphonate utilization genes in the North Pacific Subtropical Gyre

The biochemical composition of dissolved organic phosphorus (DOP) in the ocean is dominated by phosphoesters (C-O-P and C-O-P-O-C bonds), which are hydrolyzed by a diverse group of alkaline phosphatases (PhoA, PhoD, PhoX), and by phosphonates (C-P bond), which are degraded by C-P lyases and hydrolases. We designed a bioinformatics pipeline and a statistical approach to recover and analyze the alkaline phosphatase and phosphonate utilization genes from a metagenomic database derived from water samples collected from 7 depths (between 10 and 4000 m) in the oligotrophic North Pacific Subtropical Gyre. The alkaline phosphatase genes phoD and phoX were more abundant than phoA in the euphotic zone (10-130 m) and in deep waters (500-4000 m). The C-P lyase genes were most abundant in the euphotic zone at 70 m and were rare in deep water (>= 500 m) where phosphate concentrations were relatively high. These observations indicate that phosphonates are utilized primarily as a phosphorus source by bacterial C-P lyases; this is consistent with the observation that C-P lyase genes are part of the pho regulon which is expressed upon phosphorus limitation. In contrast, C-P hydrolase and alkaline phosphatase genes were often more abundant in deep waters, indicating that DOP serves mainly as a carbon and energy source in phosphate-rich deep waters which are depleted in bioavailable dissolved organic matter (DOM). The observed differences in depth distributions and presumed functions of C-P lyase and hydrolase genes indicate variability in the chemical composition of phosphonates between the euphotic zone and deep waters.