The Characteristics Of Microbial Iron Reduction And Identification Of Iron Reducers In Marine Sediments

Dissimilatory iron reduction is major form of Fe(III) oxide biomass transformation in anaerobic environment(such as marine sediment, fresh water sediment and flooding paddy soil). It is a microbial metabolism taking Fe(III) as an extreme electron accept. As a model pattern of redox process, marine sediment has an important role in studying marine ecology environment. Therefore, study of Fe(III) reduction characteristics is benefit to illustrate the reducing mechanism of iron reducers and to understand the important role of iron reduction in marine ecology environment. Iron reduction has an important theory and practice meaning on improving pollutant transformation and bioremediation.This study is taking Bohai bay sediments in China as experiment material. The iron reduction characteristics of different water quality sediments were investigated by slurry experiment, mix-culture and pure culture experiments. In slurry experiment, sediments from different sampling sites were anaerobic incubation and the rule of Fe(III) reduction change in different sediments was studied. In mixed experiment, sediment extracts from different flooding time were inoculated into Fe(OH)3 medium contained carbon sources(glucose, pyruvate, lactate and acetate). Fe(II) concentration and pH changes were mensurated termly. The active change characteristics of microbial community which have iron reducing ability was illuminated and the difference of different carbon source ability by iron reducing microbial community was compared. The results could provide theory basis to the possibility of organic pollutant decontaminating in marine sediments and information of iron reducers isolation. Strains which have iron reducing ability were isolated from sediments and were taxonomic identification and phylogenetic systematics analysis. The main results were as follows:(1) Fe(III) reduction potentials varied in different sediments. The amount of Fe(II) ranges from 3 mg·g-1 to 5 mg·g-1 except sample S7 and S17. It was indicated that the amounts of iron oxide contained in different sediments varied and water quality impacted on iron reduction. The iron reduction in the sediments from Haihe river and Daku river estuaries with Grade IV water quality was the most intensive. The sediments from Dagang river and Ziya river estuaries had also high Fe(III) reduction capacity. In contrast, Fe(III) reduction process in sediments far away from coast with Grade I water quality was inconspicuous. There was a negative correlativity between Fe(II) maximum accumulation (a) and NO3-—N, whose correlation coefficient was -0.8345. It was suggested that NO3- was a competing electron acceptor to Fe(III) in sediments.(2) In mix culture model, we integrated the indicators like Fe(III) reduction rate (%), the largest reaction rate (Vmax) and the time of Vmax (k), the characteristic of iron reducing microorganism community from different flooding recovery period using various carbon sources, showed: 15 d >5 d >1 d,glucose>pyruvate>lactate>acetate. Fe (III) reduction among different recovery incubation time using different carbon sources in Grade I and II water quality, that hyper Grade III and IV water quality. Microorganism communities under iron reduction from different flooding period had rapid response on lactate in monitoring site S2. Microorganism communities under iron reduction from different flooding period had slow response on four kinds'carbon in monitoring site S14.(3) 21 iron reducing strains were isolated from 6 kinds of marine sediments. A majority of strains in this study had the similarity colony characteristics: colonies were small, white, flat, round, opacity, surface smooth and producing sourness during incubation. Strains S3-1,S6-2,S7-4,S8-2,S14-2 and S17HQ were G+, rod-shaped, round-end. They attained a logarithms growth period within 10~25 h. Strain S17HQ isolated from monitoring site S17 had efficient iron reduction ability, which could reduce completely citrate-Fe in 12 h and ferrihydrite in 40 h(the rate of Fe(III) was 95%.(4) The paper displayed glucose and pyruvate are the optimal carbon sources of the 6 strains. When used with glucose, the Fe(III) reduction and reactive rate of them were maximum, and the maximal potential of Fe(III) reduction was in proper order for: S17HQ>S6-2>S7-4>S14-2>S8-2>S3-1.(5) Through the 16S rDNA sequence analysis and homology comparison, strain S3-1 has 99% similarity to Bacillus anthracis strain; strain S7-4, S17HQ have 99% similarity to Paenibacillus sp.; strain S14-1 has 99% similarity to Bacillus mycoides; the similarity between strain S6-1 and Bacillus megaterium reached 99%. The strains had high homology with Bacillus and had close relations in evolution relatives. Strain S8-2 has 95% similarity to Clostridium butyricum; strain S14-3 has 99% similarity to Clostridium pasteurianum; strain S14-2 has 99% similarity to Clostridium sp. Fanp3. Strains S14-2, S14-3 and S8-2 had close relations in evolution relatives, and had had high homology with Clostridium.