Dinoflagellate Proton-Pump Rhodopsin Gene in Long Island Sound: Diversity and Spatiotemporal Distribution

Microbial proton-pump rhodopsin (PPR), an alternative light-harvesting mechanism to chlorophyll-based photosystems, may contribute significantly to solar energy entry into the marine ecosystem. PPR transforms solar energy to cellular energy used for various metabolic processes in the cells or flagellar movement. Although rhodopsins or their encoding genes have been documented in a wide phylogenetic range of cultured dinoflagellates, information is limited about how widespread and how spatiotemporally dynamical dinoflagellate PPR (DiPPR) are in the marine ecosystem. In this study, using the quantitative PCR method, we investigated the abundance and diversity of DiPPR genes in Long Island Sound (LIS), a temperate estuary, both spatially and temporally in 2010. DiPPR genes were found year-round and throughout LIS, with higher abundances in the eutrophic Western Sound and during April and July. The gene diversity data suggest that there are at least five distinct rhodopsin-harboring groups of dinoflagellates throughout the year. The abundance of DiPPR genes, measured as copy number per mL seawater, appeared not to be influenced by water temperature and nitrogen nutrient concentration; however, weak negative correlations with orthophosphate concentration and salinity and a positive correlation with the abundance of typical-DiPPR-harboring dinoflagellates were observed. The association of DiPPR with phosphorus nutrition warrants further studies.