Effect Of Flooding Time On Community Structure And Abundance Of Anaeromyxobacter In Paddy Soil

Microbial Fe(Ⅲ) reduction coincided with a strong suppression of methanogenesis because of competition for hydrogen and acetate in anoxic rice paddy soil. Therefore, it has been an effective pathway to control methanogenesis by regulating microbial iron reduction processes in rice field soil. Results showed that Anaeromyxobacter could utilize crystalline iron oxides as electron acceptors to support growth, so its iron reduction was attracted great attention. Anaeromyxobacter has been isolated from anoxic sediments and rice paddies, and 16S rRNA gene sequences of Anaeromyxobacter have been retrieved from rice roots and paddy soils. However, compared with well-known Geobacter sp. capable of dissimilatory iron reduction, there was still little understanding of Fe(Ⅲ) reduction mediated by Anaeromyxobacter. Although it has been reported that iron oxidizing phases, heavy metal ions, electron donors, pH and temperature and so on had some effects on dissimilatory iron reduction in paddy soil, few investigations have been focused on the relationship between iron-reducing microorganisms and iron reduction potentiality of rice paddy soil. Thus, in this study, dynamic succession of community structure and abundance of Anaeromyxobacter were analyzed during flooding incubation to understand the correlation between the dynamic changes and characterization of microbial iron reduction in rice field soil. This report extends the theoretical foundation for the environmental function of Anaeromyxobacter in paddy soil.Soil was taken from drained paddy field after harvesting, located in Hanzhong and Zhejiang, respectively. Anaeromyxobacter community structure were obtained by PCR restriction fragment length polymorphism (PCR-RFLP) analysis from the anoxic paddy soil microcosms at 1 h, and 1, 5, 10, 20 and 30 days after flooding. Relative abundance of Anaeromyxobacter was determined by real time PCR. Reduction of Fe(Ⅲ) in rice paddies was determined with anaerobic slurry incubation method. The main results were as follows:1. The biggest iron(III) reduction potential, the biggest rate (Vmax) and the corresponding time of the largest aggregate (TVmax) in paddy soil from Hanzhong were 10.16 mg/g, 1.064 mg/(g·d) and 4.84 d, respectively; the biggest iron(Ⅲ) reduction potential, Vmax and TVmax in paddy soil from Zhejiang were 8.270 mg/g, 1.341 mg/(g·d) and 3.36 d, suggesting that iron(Ⅲ) reduction potential of Hanzhong rice soil was markedly different from Zhejiang paddy soil. 2. During flooding treatment, OTUs obtained from clone libraries of Hanzhong rice paddies were 41, 37, 51, 31, 62 and 66 respectively, and Coverage value was ranged from 73.79% to 90.40; OTUs gained from Zhejiang rice paddies were 43, 42, 43, 49, 39 and 45 respectively, and Coverage value was from 80.45% to 89.60%. Distinct dominant patterns existed in each treatment.3.αdiversity indices illuminated that there were distinct differences among flooding treatments. Diversity was the highest in HZ-20d and the lowest in HZ-10d. The maximum diversity was in ZJ-30 and the minimum in ZJ-20d. Community similarity was the highest in HZ-1d and ZJ-1d and the lowest in HZ-20d and ZJ-20d. Generally speaking, the similarity was low among different flooding treatments and among different paddy soils.4. 11 and 10 dominant patterns, which occured dynamic succession, were found in Hanzhong and Zhejiang soils, respectively. The analysis of 16S rRNA gene phylogenetic tree suggested that all of dominant patterns belonged to Anaeromyxobacter from anoxic paddy soil. Predominant patterns in Hanzhong paddies were divided into 3 groups, and all the five patterns in Group1 were affiliated with Anaeromyxobacter capable of dissimilatory iron reduction. 10 dominant patterns in Zhejiang samples were divided into Group4 and Group5, and patterns in Group5 were closely related to Anaeromyxobacter capable of dissimilatory iron reduction.5. Relative abundance of Anaeromyxobacter was fluctuant during flooding incubation. In Hanzhong samples, the lowest relative abundance of Anaeromyxobacter was 0.588% in HZ-1d and the highest was 5.150% in HZ-30d. In Zhejiang samples, the lowest relative abundance of Anaeromyxobacter was 0.024% in ZJ-1h and the highest was 0.514% in ZJ-10d. Abundance of Anaeromyxobacter in Hanzhong was higher 1 order of magnitude than Zhejiang.On the whole, community structure and relative abundance of Anaeromyxobacter are different in different types of paddy soils. However, there are dynamic changes of community structure and the abundance of Anaeromyxobacter during flooding incubation and such a variation is closely related to the potentiality of microbial iron reduction in paddy soil.