Prymnesium parvum (golden alga) is a singled celled microscopic haptophyte that can form toxic blooms and cause considerable ecological and economic consequences in freshwater systems. Understanding how the interactions among the planktonic microbial community, phytoplankton, and zooplankton may lead to either an increase or a decrease in golden algal densities has potential for conservation of aquatic species. Some studies have suggested that algicidal bacteria and allelopathic phytoplankton might prevent P. parvum blooms. The microbial structure and composition of two lakes in west Texas (Lake Ransom Canyon and Lake Colorado City) containing P. parvum was determined and the association of the bacterial community composition with the occurrence and abundance of P. parvumwas studied monthly for a year (April 2013-April 2014). Water temperature was measured at each collection site and time, and grab water samples were collected for determination of golden alga abundance using a hemocytometer and for extraction of environmental DNA (from 100–150 mL) using a DNA isolation kit. Community-level DNA sequencing was performed using a 454-pyrosequencing platform targeting the 16S rRNA gene. Relative abundances (percent bacterial occurrence) were calculated for each taxonomic unit (phylum, class, order, family, genus and species) out of the total detected for each community for each sample. Principal component analysis (PCA) was used to visualize the interaction patterns among the specified microbial taxonomic information using Lakes and Season as a grouping variables.
Results/Conclusions
Golden alga abundance was generally much lower in Lake Ransom Canyon (year average, 7600 cells ml-1) than Lake Colorado City (68500 cells ml-1), and peak abundances were observed in spring and fall in Lake Ransom Canyon, and only in the fall in Lake Colorado City. At the class level, the class Cyanobacteria was the most dominant microbial class in Lake Ransom Canyon (year average, 59%) and Lake Colorado City (55%), followed by Sphingobacteria (6%) and Betaproteobacteria (5%) in Lake Ransom Canyon and by Actinobacteria (6%), Alphaproteobacteria (6%) and Flavobacteria (5%) in Lake Colorado City. Results of PCA suggested that each lake was associated with specific assemblages of bacteria. Bacterial groups associated with Lake Colorado City (high algal abundance) are primarily Deltaproteobacteria and Cyanobacteria, whereas the dominant groups associated with Lake Ransom Canyon (low algal abundance) include Actinobacteria and Verrucomicrobia. Certain groups of bacteria were associated to winter and others to the warmer seasons. These findings may indicate that the bacterial community composition may control or influence golden alga abundance and bloom formation.