| Cyanobacterial harmful algal bloom species (cyanoHABs) have been expanding into previously bloom free waters and can have detrimental impacts on the aquatic systems in which they proliferate. This study uses both ecological and molecular approaches to characterize the composition and N2 fixation activity of the cyanoHAB communities present in the Neuse River Estuary (NRE), North Carolina and the freshwater lake system in northeastern Florida, USA. Additionally, methods were developed for detecting target species before they reach bloom proportions.; N2-fixing cyanobacteria were widely distributed throughout the NRE, but were most commonly found in the mesohaline section where the estuary widens and residence time increases. There was a relatively low genetic diversity of N2-fixing cyanoHAB species in this system, but a consistent community was present from year to year. The heterocystous cyanobacterial species Anabaena sp. and Anabaenopsis sp. and a non-heterocystous species related to Lyngbya sp. were the most commonly identified based on nifH sequence analysis.; Species-specific, DNA-based methods were developed for the detection of the cyanoHAB species Cylindrospermopsis raciborskii in many lakes throughout Florida. There was a high degree of genetic similarity in C. raciborskii populations within and between most of the Florida lakes sampled. C. raciborskii strains originating from different parts of the US and Brazil also were genetically very similar to the Florida strains, suggesting that these populations all originated from a common source relatively recently.; Maximum rates of N2 fixation in C. raciborskii, both in natural populations and cultured isolates, are during the early afternoon, but nighttime nitrogenase activity rates can be up to 70% of maximum daytime rates. Both nifH mRNA transcripts and nitrogenase proteins were present in C. raciborskii cultures throughout the diel cycle and metabolic inhibitors were used to show that nifH was being transcribed before dawn and nitrogenase proteins synthesized just after dawn. This data suggests that N2 fixation in this species depends on light availability. Thus, cyanoHABs were ubiquitous in the two systems studied and molecular approaches were demonstrated to be useful in both detecting and characterizing the activity of these populations. |
