Viral Diversity In The Deep Biosphere Of The Baltic Sea

As the most abundant and diverse biological group in the ocean,viruses play an important role in the marine ecosystem.Via infection,viruses not only shape the diversity and structures of microbial community,but also affect the biogeochemical cycle in the ocean.However,we know little about the ecological characteristics and functions of viruses in the marine sediments.For my dissertation,deep sediment from the Baltic Sea is used to investigate the viral diversity and community structures.Firstly,I performed the evaluation of the efficiencies of four grinding beads in extraction of microbial DNA in marine sediment.Then,marker gene psbA was used to explore the diversity and community structures of cyanophages and their hosts.The diversity and geographical distribution of T4-like cyanophage were further investigated by using DNA polymerase gene g43.The main conclusions can be summarized as follows:1.The extraction efficiencies of marine sediment microbial DNA with grinding beads were compared by setting four groups:group A(1.4 mm ceramic beads,0.1 mm silica beads and 1 4 mm glass beads),group B(0.6 g 0.1 mm glass beads and 0.5 mm glass beads),group C(1.2 g of 0.5 mm glass beads)and group D(1.2 g of 0.1 mm glass beads).The results showed that,for the marine sediment with high microbial abundance,group B and group C could retrieve higher concentration of dsDNA.However,for the sediment with low microbial abundance,there was no significant difference in the extraction effect of four groups of grinding beads.2.The results based on psbA analysis show that there are diverse cyanophages in the Baltic Sea sediment,and the cyanophage community structure has significant correlation with the geographical environment.Sediments,sampled from 59C and 59E near the open sea,have higher diversity and richness of microbial communities than those from 65C and 63E sites,but 65C and 63E sediment have more specific microbial groups.Most of psbA-containing organisms belongs to microbial eukaryotic algae,cyanomyovirus and cyanopodovirus in the Baltic sediment.3.Based on the analysis of g43 in the Baltic Sea sediment,we found T4-like cyanophage diversity is relatively low,and the species diversity of 65C and 63E sites is higher than that of 59E.There are significant differences in the community structure among the three sites.While in terms of vertical distribution,the diversity and community structure of T4-like cyanophage also has significant correlation with sedimentary depths for samples from 59E and 63 E,especially for the sediment from the glacial lacustrine and Holocene in 63E.Phylogenetic tree of g43 amino acid sequences can be divided into seven clusters,and OTUs shared by different sites are obviously distributed in different cluster.