Identification Of Clostridium Strains In Taihu And The Diversity Of Culturable Anaerobic Bacteria From The Gut Of Hospitalitermes Sp.

The biosphere is an extremely large and complicated ecological system,in which there are a large number of anaerobic bacteria.Despite of their huge abundance and wide distribution,very few of anaerobic bacteria were isolated until so far.In this thesis,the anaerobic bacteria from two different ecological environments,the decomposing algal scum from Taihu Lake and the gut of a higher termite,were studied,which is significant for the enrichment of our comprehension of the physiological properties and ecological functions of the anaerobic bacteria.The main results are as following:1.The characterization of three Clostridium strains isolated from the decomposing algal scum of Taihu Lake with a polyphasic approach.Three bacterial strains?MB9-7,MB9-9 and MB8-21?isolated from the decomposing algal scum of Taihu Lake were characterized using a polyphasic approach.Phylogenetic analysis of 16S rRNA genes showed that strains MB9-7 and MB9-9 were closely related to each other?99.7%similarity?and most closely related to Clostridium tyrobutyricum JCM11008^T at a similarity of 96.5%.The two strains were Gram-staining-positive,rod-shaped.Growth occurred at 20-45 ?,at pH 4.0-8.0 and at NaCl concentrations up to 2%?w/v?.Acid was produced in fermentation of glucose,xylose and so on.Acid phosphatase activities was present.The predominant cellular fatty acids were C_14:0 and C_16:0.Their cellular polar lipids were composed of phosphatidylglycerol,diphosphatidylglycerol,phosphatidylethanolamine and six unidentified polar lipids.The DNA G+C contents of strain MB9-7 and MB9-9 were 27.9 mol%and 28.7 mol%,respectively.These results supported the assignment of the new isolates to the genus Clostridium and also distinguished them from the previously described Clostridium species.Hence,it is proposed that strains MB9-71 and MB9-9 represent a novel species of the genusClostridium,with the name Clostridium algifaecis sp.nov.The type strain is MB9-7^T?=CGMCC1.5188^T=DSM28783^T?.Strain MB8-21 was closely related to Clostridium leptum with the similarity of 91%.Growth occurred at 20-50 ?,at pH 4.0-8.0 and at NaCl concentrations up to 1%?w/v?.The DNA G+C content of strain MB8-21 was 43.2 mol%,and the predominant cellular fatty acids were C_14:0 and C_12:0.The primary study indicated that strain MB8-21 is a novel species of the genus Clostridium.The studies of the three new isolates enriched our knowledge of the bacteria in the genus Clostridium,which also forms the basis of fUrther study of the relationship between Clostridium bacteria and the cyanobacteria bloom.2.The study of culturable anaerobic bacteria from the gut of Hospitalitermes sp.The diversity of culturable bacteria from the gut of a higher termite Hospitalitermes sp.was studied under anaerobic conditions.A total of 48 anaerobic and facultative anaerobic bacteria were isolated from the foregut and midgut of this termite with R2A medium.All these bacteria were facultative anaerobes that affiliated with the genera Enterobacter,Lactococcus,Lactobacillus and Serratia.The most abundant bacteria were Lactobacillus strains which occupies 54.17% of the total isolates.The 16S rRNA gene of strain R2A-40 was closely related to Lactococcus fujiensis NJ317^T and with a similarity of 94%,indicating that this bacterial isolate represents a possible new bacterial species.From the hindgut of Hospitalitermes sp.59 anaerobic and facultative anaerobic bacterias were isolated with JM-4 medium.The most dominant isolates were strict anaerobes like Clostridium and Bacteroides.The others were facultative anaerobes.Among them,Clostridium strains were the most abundant ones that accounted for 71.2% of the total bacterial isolates.For the screening of cellulose-degrading bacteria 22 bacterial strains were isolated from the enrichment culture of gut fluid obtained from the whole gut using a rice straw medium.The main isolates were strict anaerobes of the genera Clostridium and Desulfotomaculum.Clostridium strains predominated in the total bacterial isolates.The analysis of the diversity of the culturable anaerobic and facultative anaerobic bacteria showed that the distribution of symbiotic bacteria was closely related to the ecological environment of termite intestinal tract,and most of the strict anaerobes inhabit hindgut paunch that is lack of oxygen.Bacteria in the genera Clostridium and Bacteroides are dominant symbionts in the gut of wood-feeding higher termites.The results of this work form a solid basis of further study on the mechanisms of symbionts-aiding digestion of lignocellulose in the gut of termites.