Diversity And Spatial Distribution Of Fungi In Dianchi Lake Of Yunnan Plateau

Dianchi Lake is the sixth largest freshwater lake in China.As the lake is contiguous to Kunming city,its water is seriously affected by human activities.Therefore,it is also regarded as one of the three most eutrophic lakes in China.Life in Dianchi Lake,like many other organisms in the freshwater ecosystems which are close to the areas with intensive human activities,are affected significantly by the effluents and other anthropogenic pollutants.Dianchi Lake,as a typical and serious eutrophic lake in China,has gotten much attention and been managed and improved through the implement of environmental engineering projects and policies.Furthermore,many previous findings have improved our understanding on the distributions,change regulations and influences of pollutants,nutritive salts and organisms such as algae,zooplankton,bacteria,and archaea in Dianchi Lake.However,fungi in Dianchi Lake seem to be ignored for a long time.Only a few researches were carried out on them based on traditional culturable methods,even in a new age that high-throughput sequencing is commonly used to study microbial diversity and community structure.In consideration of the fact that fungi play a crucial role in biogeochemical cycling and food web in freshwater ecosystems,one aim of this study was to use high-throughput amplicon sequencing to investigate the fungal community in Dianchi Lake to address the following questions:?1?what are the fungal diversity in Dianchi Lake,?2?does the fungal community structure change in different seasons,?3?does the fungal community structure differ between surface water and sediment,?4?does the fungal community structure vary among different regions and sites,?5?what environmental factors mainly influence the fungal community,and?6?which fungal species playing an important role as‘keystone species'in surface water and sediment?Another aim of this study was to use traditional pure culture techniques to isolate yeast strains from the surface water of Dianchi Lake,then to evaluate of diversity and to assess of extracellular enzymatic activities of the culturable yeast in Dianchi Lake based on this strain resources.Furthermore,if any novel species was found from them,the research of polyphasic taxonomy will be carried out to describe the new taxa.The main results of this thesis are as follows:?1?Dianchi Lake had rich diversity of fungi.The fungi in the surface water samples and sediment samples collected from Dianchi Lake was analyzed using Illumina Hiseq platform with primers targeting the internal transcribed spacer 2 region.A total of5,489,480 reads belonging to 6,343 operational taxonomic units?OTUs?were observed.A total of five phyla,37 classes,131 orders,299 families,and 548 genera were identified from the OTUs.The fungal community in Dianchi was dominated by Ascomycota?40.7%?,followed by Basidiomycota?35.6%?,Zygomycota?10.5%?,Chytridiomycota?10.0%?and Glomeromycota?3.2%?.The dominat genera were Alternaria?2.1%?,Acaulospora?1.9%?,Neocosmospora?1.1%?,Rhizophydium?1.0%?,Massarina?1.0%?,Lobulomyces?0.9%?,Paranamyces?0.6%?,Gibellulopsis?0.5%?,Rhizopus?0.2%?,and Paludomyces?0.2%?.?2?Fungal communities in Dianchi Lake showed a remarkable change in sediments between different seasons but a slight one in surface water.?3?The results based on high-thoughtout sequencing data showed that there were significant differences between communities of surface water and those of sediments in Dianchi Lake,no matter in autumn or in spring.?4?There was a distinct community structure difference between Waihai region and Caohai region,and were also distinct community structure among the northern,middle and southern regions of Wauhai.Some sites showed interesting fungi distribution patterns.For example,site 14 was close to the only outlet of Dianchi Lake.The effluent could mainly derive from the water body flowing though the site 13 or site 15 or both.The UPGMA clustering tree showed that the sediment fungal communities of site 14,either in autumn or in spring,were more similar to those of site 13 than those of site 15;conversely,the surface water fungal communities of site 14 in two seasons were all more similar to those of site 15 than those of site 13.The results suggested that fungal communities are associated with different types of rivers inflowing into Dianchi Lake,which flow through different areas.?5?Canonical correspondence analysis?CCA?showed that the surface water indices?except TN?,including temperature,pH,EC,turbidity,TOC and TP,showed significant correlations with the fungal community composition of surface water.The sediment indices?except NH₄⁺-N?,including TOC,TN,TP,NO₃^--N and NO₂^--N,showed significant correlations with the fungal community composition of sediment.?6?Network showed that fungal taxa in sediment had closer relationships among each other as compared with those in surface water.?7?Based on traditional pure culture technique,a total of 748 yeast strains were isolated from the Dainchi Lake water,belonging to two fungal phyla?Ascomycota and Basidiomycota?,eight classes,14 orders,23 families,53 genera and 115 species.?8?Four species of four genera,including Aureobasidium pullulans,Filobasidium magnum,Naganishia albida and Rhodotorula mucilaginosa,were discovered in more than 9 sites and were also the most abundant species in all isolates?9?Three diversity indices,including D_Ma,D and H',all indicated that the diversity of culturable yeasts in different regions of Dianchi Lake was:Waihai eastern region?Waihai weatern region?Waihai southern region?Caohai region.?10?All yeast strains were screened for activities of extracellular lipase,amylase,pectinase,cellulase,protease,chitinase and laccase.Most of strains exhibited amylase activity,about 40%of the strains exhibited lipase activity,and about 20%of the strains exhibited pectinase and/or cellulase activities.?11?Three strains?YIM-HL1107^T,YIM-HL1045,YIM-HL1112?representing a novel yeast species were isolated from surface water samples collected from the Caohai region of Dianchi Lake in Yunnan,south-western China.On the basis of morphological,physiological and biochemical characteristics and sequence analysis of the D1/D2 region of the LSU rRNA gene and the internal transcribed spacer?ITS?region,they were assigned to a novel species of the genus Hannaella.The name Hannaella dianchiensis sp.nov.is proposed.The type strain is YIM-HL1107^T.