Using Molecular Probes to Detect Cyanobacterial Communities and Phosphorus Utilization in the Great Lakes

We examined the genetic potential of picocyanobacteria to recruit different sources of organic phosphorus, as well as their capacity to switch from phospholipids to sulfolipids in both Lake Erie and Lake Superior. The pelagic regions of Lake Superior and eastern Lake Erie are typically P-limited environments, and picocyanobacteria of the genus Synechococcus are the dominant primary producers during the summer. Specifically, the ability of endemic microbes to assimilate organic phosphates and phosphonates have been examined. As a proxy for their utilization of these substrates, the expression of two genes, phnD and phoX have been monitored. The phnD gene encodes the phosphonate binding protein of the ABC-type phosphonate transporter, whereas the phoX gene encodes a calcium-dependent alkaline phosphatase. To assess the ability of freshwater Synechococcus spp. to substitute sulfolipids for phospholipids, sqdX gene expression was monitored. The sqdX gene is a gene essential for sulfolipid biosynthesis and encodes the cyanobacterial sulfolipid synthase. We have developed PCR primers to detect the presence of all three genes in the endemic picocyanobacteria, and RT-PCR is being used to examine the patterns of expression that serve to assess the degree of P-stress experienced in the phytoplankton. To date, we show that the phnD gene is constitutively expressed, suggesting that freshwater picocyanobacteria are metabolizing exogenous phosphonate compounds in the severely P-limited environments. In contrast, phoX is regulated by P bioavailability in Great Lakes picocyanobacteria. We also provide evidence that sqdX is expressed during increased growth rates in phosphorus-replete conditions