A Preliminary Study On The Diversity Of Cyanophage And Its Host Cyanobacteria In Eutrophic Lakes Of Yunnan Plateau

For man-made pollution, the status of water quality pollution of Dianchi Lake and other lakes is on medium or severe level of entrophication in Yunnan province. In the recent 20 years, the serious eutrophication of water in these lakes results in water blooms occurs frequently and causes bad influence to people, especially in Dianchi Lake. Cyanophage is a kind of virus specifically infecting cyanobacteria, playing an important role in influencing host populations throughout the process of water bloom. Therefore, it is widely regarded as a possible biological tool to control the cyanobacteria bloom.In order to reveal the species distribution and quantity variation of cyanobacteria and cyanophage in entrophication plateau lakes of Yunnan. In this study we take the Dianchi Lake as our main object, and also relate to another four plateau lakes, such as Fuxian Lake, Xingyun Lake, Yilong Lake and Qilu Lake located in central and southern of Yunnan. Preliminary studied the features of the species distribution and quantity variation of cyanobacteria and cyanophage in Dianchi Lake and others entrophication plateau lakes follows the change of seasons and geographical location.Firstly, the water quality parameters, such as water temperature, pH value, total nitrogen, total phosphorus and chlorophyll-a are analyzed. There are three conclusions can be drawn.1. The appropriate temperature and alkaline pH values within this five lakes are suitable for algae growth. The content of chlorophyll-a was correlated well with eutrophication.2. The content of chlorophyll-a in Haigeng water was very high, and with a seasons changed influenced by water temprature. The total nitrogen has a high content, no longer a limited factor. Besides, the content of chlorophyll-a in individual areas, such as Haigeng Park were influenced by some weather factors (like the effect of wind).3. From north to south in Dianchi Lake, the content of chlorophyll-a reduced gradually, and were seriously influenced by total phosphorus.Secondly, the morphological diversity of algae and viruses were clearly observed by light microscope and transmission electron microscopy(TEM); The genetic diversity of cyanobacteria and cyanophage have been demonstrated by constructed phylogenetic trees based in DNA sequence of cyanobacteria 16S-23S rDNA internal space (ITS) and cyanophage capsid assembly protein gene g20; Nested-PCR is used to specifically amplify the putative phage tail sheath protein encoding gene g91 from freshwater cyanomyoviruses that infecting the Microcystis aeruginosa..Through studying the changing relation between water temperature and algae population structure, it can be found that Microcystis.sp becomes dominant species when water is warmer. In different areas of Dianchi Lake, the species and distributions of algal are different. The diversity of the algal in Caohai water is higher than that of Waihai waters, and Microcystis.sp as the dominant species grows in Haigeng waters. There are significant differences in cyanophage distribution characters in different lakes, which are closed to the algal host populations and the level of water eutrophication. The species of the cyanophage in these areas are adequate and complicated. In these waters, it includes common and particular cyanophage.Finally, two pairs of primers for PCR reaction are designed. One is specifically amplified the g91 gene form cyanophage that infecting the Microcystis, and the other is specifically amplify the Microcystis PCIGS gene. The SYBR Green fluorescent quantitative PCR method is used to estimate the copy-numbers of Microcystis PCIGS gene and cyanophage g91gene. It was found that the annual average contents of cyanophage and these host microcystis in Haigeng water were high. The annual average copy-number of PCIGS gene was 4.53×105 copies/ml, and this of g91 was 4.95×105 copies/ml. By Pearson analysis, the co-efficient between the gene copy-number of PCIGS and g91 is 0.839, P=0.001, N=11.2. There wasn't noticeable pertinence between the content of Microcystis and cyanophage, but they both gradually reduced from north to south in Dianchi Lake.This research preliminarily indicated that there were significant difference in the algae and cyanophage distribution characters in Dianchi Lake and other lakes. In addition, the content variation of Microcystis and cyanophage with the seasons and location were analyzed. This provides theoretical basis for the further study on cyanophage control function of algae bloom.