Vertical Distribution Of Prokaryotes And Responses To Their Environment In Honghu Lake Sediments

As a typical shallow lake of the middle and upper reaches of the Yangtze River, Honghu Lake had became eutrophic due to intensive aquaculture, industrialization and agricultural intensification over the past decades. To investigate the interaction and co-evolution between microorganisms and environmental factors, such as total C, total organic C and total N, a sediment core sample of 70 cm length has been obtained. This 0-70 cm sediment core corresponded to 117 years based on the isotopic geochronology. Moreover, the vertical changes of concentration of nutrient and property have been measured. Total organic C and total N increased significantly for upper 35 cm, and a peak occurred at 22-24 cm, then decreased. According to these properties, six bacterial and archaeal 16S rDNA clone libraries have been constructed of three significantly different layers of 10～12 cm,22～24 cm and 52～57 cm, which reflected the changes of environment and human practice. Restriction fragment length polymorphism (RFLP) patterns, sequencing and phylogenetic analysis have also been analysed.The results showed that the bacterial communities of all the three layers were related toα-,β-,γ-,δ-proteobacteria, Nitrospiraceae, Chloroflexi, Acidobacterium, Firmicutes (low G+C), Planctomyces, Verrucomicrobia, Chlorobi and Actinobacteria (high G+C). However, the upper and lower layers were very rich in Bacteroides (77% and 88%, respectively). Except a higher proportion of 8-proteobacteria (19%), the rest groups presented a uniform distribution at middle layer.The archaeal communities were composed of Crenarchaeota and Euryarchaeota in all three depths, but their community structures were significantly different. Desulfurococcales was detected only in the middle layer; Thermococci and Halobacteria were unique groups in lower layer. The proportion of Thermoplasmata had no difference between upper and middle layer (31% and 30%, respectively), but reduced to 13.9% at lower layer; Methanomicrobiales had a similar tendency in all three depths comparison with Thermoplasmata. This implied both groups had the same nutritional requirement or ecological niche. From upper to lower layers, the proportion of Crenarchaeota was 55%, 52% and 63%, respectively.In conclusion, there is evident variance of microbial community structure along the depths, and microbial community composition and diversity has been influenced by organic perturbation in different depth of sediment. These results provide an insight into the diversity and vertical distribution of prokaryotes for the first time and supply foundation to elucidate the role of microbes in the geochemical cycle.