Studies On Microbiological Characteristics Of The Gut Ecosystem Of Termite Coptotermes Formosanus

Heterotrophic bacteria, nitrogen-fixing bacteria, methanogens and cellulolytic bacteria in gut of termite Coptotermes formosanus Shiraki were enumerated, isolated and identified. Furthermore, the physiological and biochemical characteristics of the strains isolated and the biological characteristics of the termite, including the N-fixing activity, methanogenic activity and cellulolytic activity were studied. The results are reported as follows:1. Enumeration by plate-counting and rolling tube methods indicated that there were abundant symbiotic bacteria resided in hindgut of termite Coptotermes formosanus. The maximal number of heterotrophic bacteria population in the gut of termite appeared in July around. Two heterotrophic bacterial strains, strain BA and strain BD, isolated from the gut of termite, were identified as Streptococcus sp. and Enterobacter sp., respectively. Both strains were facultative anaerobes, which could grow well under 100% 02 as the initial gas phase. The strains characterized by a short lifecycle in vitro.2. The high N-fixing activity was detected in workers of Coptotermes formosanus. The N-fixing activity of the freshly collected workers was about 0.0944 u g N ?g"1 termite ?h"1. The N-fixing activity could be obviously affected by the nitrogen content of food and the termite physiological status, and even completely eliminated by the addition of streptomycin. The maximal number of N-fixing bacteria population in the gut of termite appeared in May around. The enumeration by MPN method indicated that there were about 7.5 X 102 N-fixing cells in each termite gut. Two N-fixing facultative anaerobes, strain NA and strain NB, were isolated from the termite gut, and both were identified as Citrobacter sp.. Both strainsshowed N-fixing activity under anaerobic condition. NaNOs was not a fine nitrogen source for the growth of strain NB, whereas it could inhibited nitrogen fixation of strain NB.3. Termite Coptotermes formosanus could emit large quantities of methane. The methane emission rate of the freshly collected workers was about 0.5282 nmol ?termite"1 ?h~'. The methane emission rate could be affected by the termite physiological status, and decreased markedly when termites were fed with filter paper immersed with streptomycin and penicillin. Methane emission rate of the workers incubated in atmosphere containing 20% H2. increased 1.6 folds, compared with the normal one. The enumeration by MPN method indicated that there were about 5.0 X 105 cells of hydrogen-producing acetogenic bacteria and 3.75 X 105 cells of methanogens in each termite gut.4. The activities of exo- 3 -1,4-glucouldase, endo- P -1,4-glucouldase, P -Glucosidase and xylase in workers of Coptotermes formosanus were measured. The activities of P -Glucosidase and xylase decreased significantly in the workers fed by filter paper immersed with streptomycin. Two bacterial strains, strain CA and strain CB, capable of growing well on wood dust medium were isolated from termite gut after enrichment, and were identified as Bacillus sp and Enterobacter sp. respectively.Strain CA could produce the considerable amount of exo- P -1,4-glucouldase, endo- P -1,4- glucouldase and xylase when some kinds of lignocellulosic biomass- cellobiose and xylose were used as sole carbon source. No growth, however, appeared on medium with filter paper and carboxymethylcellulose. The optimum cultural time , the concentration of yeast extract, the culture temperature and the initial pH of medium for production of lignocelluloses-decomposing enzyme by strain CA was 60h, 1.5~2.0g ·L-1, 3℃C~3℃C and 7.0-7.5, respectively.