Glycerol Utilization By Phytoplankton1

Dissolved organic carbon (DOC) is an important source of carbon and energy for microbes, but whether it can be used by phytoplankton has not been systematically studied, and the underlying molecular metabolism remains poorly understood. Here, we investigated the ability of phytoplankton to utilize glycerol as a representative of DOC. The widespread presence and expression of glycerol transporter genes were found in transcriptomes and genomes, suggesting the glycerol utilization potential in the diverse marine phytoplankton. We surveyed 29 representative phytoplankton species (31 strains) from six phyla for their ability to use glycerol. Three types of responses were found: positive utilization (Type I), no response (Type II), and negative response (Type III). In all, 11 Type I species were further investigated in axenic cultures with different glycerol concentrations, and five species showed intrinsic glycerol utilizing ability without the aid of bacteria. The ability of species to use glycerol to support non-photosynthetic (DCMU treated) growth was consistent with their possession and expression of glycerol transporter genes. However, some species from the Type II and Type III also possess and express the genes, raising a question whether glycerol transporter in algae might have diversified its function to glycerol export or even non-glycerol transport. Our results show that glycerol could serve as organic carbon source, harmless xenobiotics, or growth inhibitors for phytoplankton depending on species, indicating that glycerol, including natural sources or human discharges, may shape the marine phytoplankton community structure, especially under low photosynthetic efficiency conditions.