The effect of microbial community on golden algal growth

The marine haptophyte, Prymnesium parvum (golden alga), has now invaded freshwater ecosystems all over the world. This unicellular microbe is capable of producing toxic compounds that destroy co-occurring, mostly gill-breathing organisms and is responsible for millions of fish kills in the past few decades. This research focuses on characterizing the structure and composition of the microbial community along with the role of environmental variables in creating favorable conditions for golden alga to bloom. Lake water samples and laboratory studies were conducted to understand the associations of golden algal growth, occurrence, and abundance. From the field study: The bacterial composition and golden algal abundance were assessed in different lakes to study the effect of the microbial community on golden algal growth. Spatial (different lakes) and temporal (every month for a year) water samples were collected. Genomic DNA was extracted from the water samples. Environmental factors (water quality data) were taken at the time of sampling. Golden algal cell counts from the water samples collected were determined using a hemocytometer. Metagenomic sequencing of DNA extracted from lake water samples was used to determine the percentile bacterial composition. Principal component analysis was used to visualize the pattern and to determine the associations among the bacterial groups and algal counts. Spearman’s correlation coefficients between golden alga counts and environmental factors were computed. In the laboratory study: The effect of selected antibiotics (penicillin and streptomycin) and various combinations of vitamins (biotin, vitamin B12, and thiamine) on growth of Prymnesium parvum strain UTEX LB 2797 was studied. The culture medium used was modified F/2 medium without the silica and with sea salt added at 5 ppt (5 g per liter). Growth was monitored every three days using a spectrophotometer at 680 nm. Based on the field study the bacterial phyla Planctomycetes, Cyanobacteria, Proteobacteria, and Bacteroidetes were positively associated with high golden algal abundance and the bacterial phyla Actinomycetes, Acidobacterium, and Chloroflexi were negatively associated. Golden alga counts gave a consistent response to the environmental factors conductivity and temperature throughout the analysis. That is, temperature was negatively associated with golden alga counts and conductivity was positively associated with golden alga counts. The growth of golden alga was negatively affected by penicillin with a concentration-dependent effect but growth was fully inhibited by streptomycin at all concentrations tested. Growth was observed in the absence of supplemented vitamins. To identify possible vitamin-providing bacteria in the lab cultures of golden alga, genomic DNA was extracted from the lab culture and sequenced. Metagenomic sequencing, using Illumina MiSeq, demonstrated that golden alga coexists with bacterial groups that belong to only three bacterial phyla, Bacteroidetes, Cyanobacteria, and Proteobacteria. These bacterial phyla were also found to be positively associated with high abundance of golden alga, suggesting that they may form a potential mutualistic symbiosis providing important nutrients and vitamins to golden alga in exchange for a carbon source for their growth.