Isolation And Identification Of Novel Bacteria From The Aquatic Environments Of The East China Sea And Different Salt Lakes Of China

Earth is the home of approximately 1012 microbial species,but most of them have not been characterized yet.Aquatic environments cover most of the Earth surface and have many diverse environments which are presumably harboring numerous undiscovered bacterial taxa.Therefore,the aim of the thesis was to investigate the bacterial diversity in different aquatic environmental samples with special focus on the isolation of novel bacteria based on the culture-dependent methods and identification by polyphasic approach.Heterotrophic mesophilic and halophilic bacterial strains were recovered and phylogenetically characterized from samples collected from two totally different aquatic environments:water,sand/sediment and seaweed samples collected near Zhoushan,Zhairuo,Gouqi Islands located in the East China Sea(ECS);and water,sediment samples collected from Qinghai Lake,Heima River,and Chaka Salt Lake located in the Qinghai province,China.Overall,409 bacterial strains affiliated to Gammaproteobacteria(55%),Alphaproteobacteria(14%),Firmicutes(1 1%),Bacteroidetes(1 0%),Actinobacteria(5%)and Betaproteobacteria(5%)were isolated from these two environments.From ECS,total 302 strains were isolated where strains affiliated to Gatnmmaproteobacteria(64%)are the most dominant,followed by Bacteroidetes(11%),Alphaproteobacteria(9%),Firm icutes(8%),Betaproteobacteria(5%)and Actinobacteria(3%).On the other hand,107 strains were isolated from the salt lakes which are affiliated to Gammaproteobacteria(29%),Alphaproteobacteria(27%),Firmicutes(22%),Actinobacteria(11%),Bacteroidetes(8%),and Betaproteobacteria(3%).A total of 48 strains from ECS and 10 strains from salt lakes had?98.65%16S rRNA gene sequence similarity to the validly published species and thus might be considered as representatives of novel species.Among these possible novel strains,45%are affiliated to Gammaproteobacteria,36%to Bacteroidetes,150%to Alphaproteobacteria,2%to Firmicutes and another 2%to Betaproteobacteria.From the phyla Bacteroidetes,three novel strains has been identified and named as Flavobacterium sharifuzzamanii,F.zhairuonensis,F.chakense.Among these three,F.sharifuzzamanii and F.zhairuonensis were isolated from sediments of ECS while F.chakense was isolated from the surface water of Chaka Salt Lake.Gene cluster prediction by genome mining,microbial fermentation and antimicrobial activity experiments have been carried out preliminarily to analyze the potential of secondary metabolites in F.zhairuonensis.This study provides a reference for the study of microbial diversity in the East China Sea and salt lakes in mainland China,and identified new bacterial strains enrich the microbial resources,laying a foundation for the subsequent development and application of marine environment and Salt Lake microbial resources.Thus,the results of the present study demonstrate that aquatic habitats are a promising source for novel bacterial taxa and possible source of natural products.