Effect Of Anaerobic Enrichment Treatment On Bacterial Community Structure In Paddy Soil

Microorganisms that use metals as terminal electron acceptors, or reduce metals as a detoxification mechanism, have an important influence on the geochemistry of aquatic sediments, submerged soils, and the terrestrial subsurface. Furthermore, it is becoming increasingly apparent that microbial metal reduction may be manipulated to aid in the remediation of environments and waste streams contaminated with metals and certain organics. This research focus on iron-reducing bacteria in paddy soil under mixed carbon source model, get a better understanding of bacterial community structure changes at different stages of cultivation and provide a theoretical basis for purifying of iron-reducing bacteria.The research used paddy soil being flooding for more than six months, added artificial synthesis ferric iron and mix carbon sources and cultivated with anaerobic enrichment.16S rDNA gene RFLP study of iron reducing bacteria gave the basis of comparing difference of iron-reducing ability.There were seven cultivate period(0d,1d,7d,14d,21d,28d and 50d).108,113,112, 75,80,80 and 80 isolates of iron-reducing bacteria were selected randomly respectively with sealing-membrane anaerobic culture method,72,15,87,75,80,80 and 80 isolates of iron-reducing bacteria were selected randomly respectively with anaerobic dryer culture method. All the 1135 isolates were put onto PCR and got 682 clones. All the clones were seperated into 18,5,6,2,6,8 and 6 enzyme types,27 in total, with 11 dominant type and 14 single clone.(1) From the clone libraries of the seven different treatments(0d, 1d,7d,14d,21d,28 d and 50 d), there were18,5,6,2,6,8 and 6 restriction endonuclease types respectively, the coverage of each clone libraries were 88.5% 100% and 97.1%,98.2%,95.2% and 96.2%, which were all above 85%.(2) The a diversity index (H'and D index) and evenness PIE index showed the order as 0 d>28d>1d>50d>7d>21d>14d. Diversity index were highest in 0 d treatment, and were the lowest in 14 d. The enrichment index (dMa and R2 index) showed the orders as:0d >28d>50d>7d>1d>21d>14d。There were two fastigiums at 7 d and 28 d, which means that the bacterias were more active at 7 d and 28 d, and the ability of iron-reduction were the highest at 7 d. (3) Two method of anaerobic enrichment were compared and results showed that the anaerobic dryer is better, and the iron-reducing ability was the highest on 7th day.(4) The dominant bacteria families were identified as bacillus, staphylococcus and paenibacillus. The most potential iron-reducing bacterias distributed mainly in dominant type 1, and the similar bacteria families were staphylococcus and bacillus.These results demonstrated that the synthetic hydrated and mix carbon source brought obvious changes to the iron-reducing structure:ratio of iron-reducing bacterias and carbon using potential were raised; The bacteria community needed a longer time to reach the stable state; and bacillus and staphylococcus occupied the dominant position.