Community Structure And Lysogeny Analysis Of Heterotrophic Bacteria Associated With Cyanobacteria

Cyanobacteria are important primary producers in the aquatic ecosystem and have an important impact on the associated bacterial community in the environment.Cyanophage infection and lysis of the host affect the population dynamics and community structure of the cyanobacteria and their associated heterotrophic bacteria Lysogeny is ubiquitous in the bacterial community in the marine ecosystem.The presence and induction of prophages also affect the bacterial diversity and ecological processes in the ocean.In this thesis,we conducted the comparative analysis of heterotrophic bacterial communities associated with typical estuarine PC-rich and PE-rich cyanobacteria strains,and investigated the heterotrophic bacterial communities in the cyanobacterial cultures with or without addition of viruses,to explore the effect of cyanobacteria and cyanophage infection on their associated heterotrophic bacterial communities.In addition,the occurrence rate of lysogeny among cyanobacteria associated heterotrophic bacteria isolates,the genomics and evolution of induced prophages were analyzed to investigate the effect of viruses on bacterial community on the lysogeny level.The main results of this thesis are1.The associated heterotrophic bacteria in PC-rich cyanobacteria CBW1101 and PE-rich CBW1107 cultures both consist of Alphaproteobacteria,Bacteroidia,Phycisphaerae and Gammaproteobacteria,but the relative abundance and diversity of associated bacteria vary between the two cultures2.Viral infection and lysis of cyanobacteria increased the diversity of associated bacterial community in the CBW1101 culture.The bacterial community supported by viral lysis products of cyanobacteria is similar to that by exudates released from cyanobacteria.The highest bacterial diversity occurred in the middle phase,but not in the late phase,indicating that viral regulation of the host metabolism during infection greatly changed the DOM composition released by cyanobacteria,and had a very important effect on the change of bacterial community structure in the same environment.3.Twenty-seven isolates of cyanobacteria-associated heterotrophic bacteria were composed of Gammaproteobacteria,Alphaproteobacteria,Actinobacteria and Flavobacteria.The occurrence rate of lysogeny among isolates was about 21%,which was lower than what has been reported for marine bacterial isolates.4.Genomic analysis of the three prophages revealed that more than half ORFs have unknown function.The phylogenetic analysis based on the amino acid sequence of terL shows that Propl,Prop2,and Prop3 represent different types of unknown viruses.Three prophages have the same integration mechanism,lack common genes related to DNA replication and metabolism,and encode diverse transcriptional regulators in each genome.Their potential in regulating host metabolism implies the effect of prophages on the diversity of their hosts.5.The RcGTA-like structures in Prop1 and Prop2 are highly similar to RcGTA in terms of the related protein gene arrangement,with 1-2 genes homologous to that of RcGTA.Multiple genes in Prop1 and Prop2 RcGTA-like structures have a distant evolutionary relationship with the GTA sequence,this provided supports to the hypothesis that RcGTA is evolved from a prophage ancestor.