Study Of Cyanobacteria Community Structure And Functional Gene Expression Traits During Bloom Period In William H Harsha Lake

In order to reveal the mechanism of algal bloom breakout in freshwater lakes of temperate region,we collected water from William H Harsha Lake located in the east of Cincinnati about 40 km in Ohio,USA from May to September 2015 to investigate the content of nitrogen and phosphorus nutrient during algal blooms.16S rRNA amplified molecular sequencing technology and bioinformatics statistics were used to analyze the characteristics of species composition of cyanobacteria were analyzed,and the expression characteristics of photosynthesis,respiration,stress resistance gene,RNA,protein,carbon,nitrogen and phosphorus were analyzed by macrotranscriptomics method.The results showed that:(1)The average contents of nitrogen and phosphorus nutrients were the highest in sample of EFL(total nitrogen 1479.93μg/L,ammonia nitrogen 177.87μg/L,nitrite nitrogen 30.46μg/L,nitrate nitrogen 586.79μg/L,total phosphorus 127.97μg/L and total reactive phosphorus 112.31μg/L).The average contents of total nitrogen(1460.05μg/L),nitrite nitrogen(15.43μg/L),nitrate nitrogen(218.63μg/L),total phosphorus(80.77μg/L)and total reactive phosphorus(49.88μg/L)were the highest at CGB sampling sites which was coastal lake outlets affected by human activities and upstream water flow.The nutrient content of five samples reached the peak value from late June to early July during the bloom period.(2)By analyzing the composition characteristics of cyanobacteria species at each sampling site,it was found that all OTUs belonged to the subclasses of Nostocophycideae,Oscillatoriophycideae and Synechococcophycideae.The top three of the five sampling sites with high relative abundance were Planktothrix(25.77%),Aphanizomenon(12.71%)and Cylindrospermum(7.25%)genus.The relative abundance of Planktothrix was much higher in the site of higher nutrient than site of lower nutrient content.Phylogenetic trees based on 16S rRNA showed that dominant cyanobacteria had higher intraspecific diversity,while non-dominant cyanobacteria did not perform this characteristic;(3)The expression characteristics of functional genes in BUOY sampling sites(lake center area)showed that photosynthesis functional genes were higher than other physiological genes during the peak period of cyanobacterial blooms.The expression level of metabolic-related functional genes remained at a very high level all the time;the expression level of respiration related functional genes was stable,indicating that the cyanobacterial community was in an active and vigorous stage of growth and metabolism,which provided the necessary material and energy basis for the continuous spread of cyanobacterial bloom.The expression level of nitrogen and phosphoru functional genes were highly related with content of nitrogen and phosphorus nutrients content of sampling sites.The relative abundance of Pst S gene,total phosphorus(R~2=0.76,P<0.01)and total reactive phosphorus(R~2=0.49,P<0.05)showed that the expression of Pst S gene was negatively correlated with the concentration of total phosphorus and total reactive phosphorus(P<0.05).The expression of nutrients metabolism related genes indicates that nitrogen and phosphorus indeed affect the occurrence and development of algae blooms from the perspective of their physiological and metabolic activities.In this study,modern molecular biological method and bioinformatics statistics were combined to reveal the species composition characteristics of cyanobacterial bloom in temperate freshwater lakes.The mechanism of cyanobacterial blooms in temperate inland lakes was revealed from the perspectives of external environmental factors and intrinsic functional gene expression level.It has provided important theoretical reference value and scientific guiding significance for the control of cyanobacterial bloom.