Sequence diversity and expression levels of Synechococcus phosphate transporter gene in the East China Sea

Abstract

The phosphate-binding transporter gene (pstS) is a potential diagnostic marker for inorganic phosphorus stress in picocyanobacteria. In order to evaluate pstS messenger (m)RNA levels in the East China Sea (ECS) by real-time quantitative reverse transcription polymerase chain reaction (Q-RT-PCR), suitable primer sets had to be designed according to local gene diversity. For this purpose, 71 homologous pstS sequences were collected during 3 cruises conducted in March 2006, and April and July 2007. The phylogenetic analysis indicated that all pstS sequences obtained from the continental shelf region in the northern ECS belonged to Synechococcus clades II, III, and V. In contrast, only a small fraction of pstS sequences obtained in the Kuroshio region was from Synechococcus. According to sequence alignment, a degenerate primer set was designed for Synechococcus. The specificity of the primers was confirmed using genomic DNA extracted from several Synechococcus and Prochlorococcus cultured strains. Subsequently, in the spring seasons of 2007 and 2008, the pstS mRNA abundance was measured by the Synechococcus-specific primer set at a station in the oligotrophic Kuroshio Current adjacent to the ECS. It was found that the pstS expression pattern was inversely correlated with the concentration of inorganic phosphate in surface waters, which closely resembled an analogous relationship in a cultured Synechococcus. A similar relationship was formed between pstS expression and the previous-day aerosol particles, but nonexistent regarding mixed layer depths.