Genetic Diversity And Spatial And Temporal Dynamics Of T4-like Myoviruses In The Jiulong River Estuary

Viruses are the most abundant biological entities on Earth and play an important role in regulating microbial abundance and community dynamics,and impact on global biogeochemical cycles.It is clear that viruses constitute the greatest genetic diversity in the ocean.The research of viral diversity can help us to understand the role of virioplankton in the microbial ecosystem and biogeochemical cycles.Estuaries are the vital,dynamic jointing ecosystem of inland waters and oceans.Under the influence of natural and anthropogenic factors,estuarine ecosystems are a basin for microorganisms originating from river,ocean and soil,and show great diversity and complex community structure.At the same time,due to the mixing fronts of marine tidal waters,river outwelling waters and human domestic sewages,estuaries provide novel habitats for microbes.Investigation of microbial diversity and community structure can help us to understand the ecological function and biogeochemical cycle of estuarine ecosystem,which is vital for the sustainable development of estuarine area.The main outcomes include:(1)The abundance of virioplankton communities in a typical subtropical estuary,the Jiulong River Estuary(JRE)in China were investigated by flow cytometry,which ranged from(1.01±0.05)×107 to(1.62±0.09)×107 particles mL-1.The population size of viruses was correlated with temperature and nutrient concentration.(2)Three typical tailed viral morphotypes(myovirus,siphovirus and podovirus)and non-tailed viral morphotype were observed through the transmission electron microscopy.It indicated that the virioplankton in JRE has a high morphological diversity.(3)Detailed phylogenetic diversity and spatial variation were investigated for T4-like myoviruses via g23 genetic marker.Most of the g23 sequences in JRE fell into three previously established groups(Marine Groups,Paddy Groups and Lake Groups)as well as two novel Estuary Groups.This demonstrated the co-existence of typical inland and marine T4-like myoviruses in estuarine ecosystem,suggesting the movement of viruses and their hosts among biomes.(4)The major capsid protein gene,g23,was used to investigate the spatial and temporal dynamics of T4-like myoviruses community composition in JRE for a period of 1 year.The results show strong spatial and temporal variations of T4-like virioplankton in the JRE.Three major groups were identified(spring,summer,and autumn-winter),which resulted in a clear seasonal succession pattern.Moreover,specific T4-like myoviral OTUs(operational taxonomic units)peaked in different seasons,such as OTU1 and OTU11,which belong to Exo T-evens group,showed significant advantages in summer(June and July)samples,while OTU2,OTU3,OTU4 and OTU5 of the Marine Groups ? group showed higher abundance in the autumn-winter(October,November,December and January)samples.At the same time,we found that some OTUs with moderately abundance showed little variation on the time scales.The relative abundance of most OTUs(99%)is less than 0.01%and only 13 OTUs showed>1%proportion of total population.