Isolation and Characterization of Heterotrophic Chemoorganotrophic Bacteria from the Roots of Lepironia articulata (reedgrass) Grown on Strongly Acidic Sulfate Soil in South Thailand

Bacterial communities inhabiting the rhizosphere of Lepironia articulata (reedgrass) grown in a strongly acidic sulfate soil distributed in the province of Narathiwat, Thailand were investigated. Fresh roots of L. articulata were cut from the subterranean stem, and the bacteria were isolated from the homogenate on dilution plates of glucose-yeast extract agar medium adjusted to pH 4.5. In or on the roots, 3.3×107 bacteria(cfu)g-1 fresh roots were present. From the dilution plates, 60 bacteria were randomly isolated and their characteristics were examined. All the isolates were Gram-negative rods and grew well at pH 4.5. Analysis of cell fatty acids and the restriction fragment length polymorphism (RFLP) of PCR-amplified 16S rRNA genes indicated that the isolates could be divided into 4 groups (Group I to IV). Group I (65% of total) isolates failed to grow on the agar plate at pH 7. The sequence analysis of 16S rRNA genes of a Group I isolate showed that it resembled Acidocella facilis with 98.5% homology. Growth of Group I bacteria was suppressed by acetate. The next most abundant bacteria, belonging to Group II, grew at pH 7.0 and belonged to Burkholderia. These bacteria accounted for 28% of all the isolates. Bacteria of Group III and IV (identified as Bacillus subtilis) were a minor constituent only. Group III isolates were similar to the genus Xanthomonas, but the similarity of the 16S rRNA gene base arrangement with the nearest species was below 90%.