Diversity Of Virioplankton And Its Influencing Factors In Dianchi Lake And Fuxian Lake

Viruses,as the most abundant biological entities in aquatic ecosystems,are widely distributed in marine and freshwater environments.They play an important role in regulating microbial community composition,manipulating microbe-driven biogeochemical process,influencing their hosts through horizontal gene transfer,and affecting climate change.Currently,the most of viral ecology researches are focused on marine ecosystem.The researches on marine viral metagenomics have revealed that the marine viruses are highly diversified and extremely abundant in viral species.Whereas,the study on freshwater viral communities are still limited.The freshwater ecosystem especially freshwater lakes,as the major water sources and entertainment place,are closely related to our daily life.The viral community composition,diversity and ecological functions are worth for further study.Based on the above research background and situation,two typical plateau lakes with different nutritional status,Dianchi Lake and Fuxian Lake,were selected in this study.Viral metagenomic technology,fluorescent microscope method and culture method were used to study the density of virus-likeparticles,viral community composition and distribution patterns in the two lakes.Combined with 16S rRNA gene sequencing technology,we further studied the correlations among viral communities,potential prokaryotic host communities and environmental factors,and discussed the driving factors that potentially affected the distribution pattern.The main findings are as follows:In this study,an average of 36,997±5,309 viral contigs were obtained from the eutrophic lake Dianchi viral metagenome samples.The viral community in the surface water of Dianchi Lake is dominated by Myoviridae,Siphoviridae and Podoviridae,followed by unclassified viruses and Phycodnaviridae.The dominant viral species are Microcystis aeruginosa phage,Methyophilales phage,Brucella phage,and Synechococcus phage,Ralstonia phage,Flavobacterium phage,and Pelagibacter phag.The community composition,structure and diversity of virioplankton in Dianchi Lake showed seasonal change patterns,and the seasonal change was greater than spatial change between the north and south shores.Nutrient concentration and Chla concentration were one of the driving factors of seasonal and spatial distribution of viral community in Dianchi Lake.An average of 26,362±2,116 viral contigs were obtained from oligotrophic lake Fuxian viral metagenome samples.The dominant viral families in Fuxian Lake are consistent with Dianchi Lake,but with different relative abundance.Among them,the relative abundance of Phycodnaviridae and unclassified viruses in Fuxian Lake were significantly higher than in Dianchi Lake(p<0.05),and the relative abundance of Tectiviridae was significantly lower than in Dianchi Lake(p<0.05).The dominant viral speices with relatively high abundance in Fuxian Lake are Rhizobium phage,Cellulophaga phage,uncultured Mediterranean phage,Persicivirga phage,Synechococcus phage.There are about two third viral species commonly distributed in Dianchi Lake and Fuxian Lake,and their viral community structures are highly correlated.From the perspective of diversity,viral diversity is higher in eutrophic lake Dianchi than in oligotrophic lake Fuxian.The nutrient concentration is an important factor affecting the viral communities in the two lakes.The higher the nutrient concentration,the higher the diversity of virioplankton.It's possible that the nutrient concentration drives directly or indirectly the differences of virioplankton community and distribution of dominant species in the two lakes.This study further compared the virioplankton and prokaryotic communities in the surface water of Dianchi Lake and Fuxian Lake,through viral metagenomic and 16S rRNA gene sequencing technology.The results showed that the viral and prokaryotic diversity index(Shannon Wiener Index and Evenness Index)were opposite in each sample.Both the diversity of prokaryotes and viruses were significantly correlated with total phosphorus and nitrogen concentrations(p<0.05),but the correlations were opposite.The PCoA results of prokaryotic and viral community structures were quite similar.It is revealed that there is a close relationship between viruses and prokaryotes in community composition,structure,diversity and correlation with environmental factors.Prokaryotic community is a major factor drives the distribution of viral community.In addition,the community composition dominant prokaryotic host and predicted viral infection host at phylum level were basically the same,but the relative abundances were different.Among them,the distribution of Cyanobacteria and Actinobacteria and virus predicted to infect these two phylum hosts were opposite in the two lakes,that is higher Cyanobacteria host but lower cyanophages in Dianchi Lake than in Fuxian Lake.Further studies on Cyanobacteria and cyanophages showed that phage lysogenic infection might be widespread in Dianchi Lake.The differences in genus type,abundance,and susceptibility to lysogeny of Cyanobacteria in the two lakes might contribute to the different distribution patterns.Aeromonas species are common pathogens for human,fishes and domestic animals.The phages infect Aeromonas species were annotated in viral metagenomes from Dianchi Lake with a relative abundance of 2.95-5.77%in each sample.Therefore,in this study,we further investigated the diversity of Aeromonas phages isolated using standard plaque assays from Dianchi lake.Nine Aeromonas phages were isolated and sequenced,and they appeared to be highly diversified on morphology,genome length,GC%contents,genomic homology and evolutionary relationships.In summary,by using fluorescenct microscope,metagenomic technology and phage culture method,the results of this study showed that there are highly abundant and diversified virus in Dianchi and Fuxian Lake,and there's a close correlation in viral community composition between Dianchi Lake and Fuxian Lake.The correlation analyses with environmental factors and prokaryotic communities indicate that the trophic status(TP and TN),water temperature and prokaryotic communities in the two lakes are the main factors affecting the viral community composition and diversity in the two lakes,and the seasonal change pattern of Dianchi Lake.This study provides a good basis for further researches on virus ecology in plateau lakes.