Communities of Iron(III)-reducing Bacteria in Irrigated Tropical Rice Fields

Abstract

Field and greenhouse experiments were conducted to investigate the seasonal dynamics of microbial communities of iron(III)-reducing bacteria (IRB) in irrigated paddy soils as affected by rice cultivation system history, aerated fallow, and soil till practice at the International Rice Research Institute (IRRI). IRB were enumerated by a modified Most Probable Number (MPN) method. The average numbers of glucose-, acetate- and benzoate-utilizing iron(III)-reducing bacteria in the dry season of 1999 were 5.2×10 ⁸, 1.2×10⁶, and 5.3 ×10⁵ g^-1 dry soil respectively in the double cropping field and 5.4×10⁷, 5.9×10⁵ and 6.9×10 ⁵ g^-1 dry soil respectively in the triple cropping field. In the wet season of the same year, they were 1.5×10⁵, 8.3×10 ³ and 1.1×10⁵ g^-1 dry soil respectively in the double cropping field; and 6.4×10 ⁵, 7.0×10⁵ and 2.7 ×10⁵ g^-1 dry soil respectively in the triple cropping field. The MPN values of these IRB have different seasonal dynamics under the influence of rice cultivation history and fallow treatment in paddy soils. The results of screening and identification of enriched IRB by the BIOLOG method showed that 66% of the tested strains could be identified, among them, 58% are Pseudomonas spp., which appeared to be the predominant species of iron(III) reducers in these paddy fields.