Research Field in Agriculture, Agriculture Fisheries and Veterinary Medicine Area, Kagoshima University.
The United Graduate School of Agricultural Sciences, Kagoshima University.
Microbes Environ. 2021;36(1). doi: 10.1264/jsme2.ME20136.
The environment of plant rhizosphere soil differs from that of non-rhizosphere soil due to the secretion of mucilage polysaccharides from the roots. This environment is regarded as one of the preferential habitats for agar-degrading bacteria. In a previous study, agar-degrading Steroidobacter agariperforans KA5-B was isolated from agar-enriched agricultural soil using diffusible metabolites from Rhizobiales bacteria. Based on the hypothesis that similar characteristic bacteria still exist in the rhizosphere, isolation was performed using rhizosphere soils. Agar-degrading SA29-B and YU21-B were isolated from onion and soybean rhizosphere soils. The 16S rRNA genes of these strains showed ≥98.7% identities with the most closely related strain KA5-B. However, differences were noted in polysaccharide utilization, and average nucleotide identities were <95-96% against strain KA5-B, indicating that they are different species from S. agariperforans KA5-B. To investigate the distribution of bacterial sequences affiliated with novel strains, a primer set was designed and a meta-analysis of the 16S rRNA gene was performed. Sequences were widely distributed in rhizospheres throughout Japan, but varied in plant- and region-dependent manners. Regarding phenotypic characterization, distinguishable features were observed in growth temperatures, pH, and dominant fatty acids. SA29-B and YU21-B grew at 15-40°C and pH 6.0-12 and contained C as the dominant cell fatty acid, whereas KA5-B showed no growth at 40°C and pH 12 and contained a moderate amount of C. Based on these characteristics, SA29-B (JCM 333368=KCTC 72223) and YU21-B (JCM 333367=KCTC 72222) represent novel species in the genus Steroidobacter, for which the name Steroidobacter agaridevorans sp. nov. is proposed.
由于根系分泌粘胶多糖，植物根际土壤的环境不同于非根际土壤。这种环境被认为是琼脂降解细菌的首选栖息地之一。在之前的一项研究中，从富含琼脂的农业土壤中分离出了琼脂降解菌 Rhizobiales 细菌的可扩散代谢物，并从中分离出了琼脂降解菌 Steroidobacter agariperforans KA5-B。基于在根际中仍然存在类似特征细菌的假设，使用根际土壤进行了分离。从洋葱和大豆根际土壤中分离出了琼脂降解菌 SA29-B 和 YU21-B。这些菌株的 16S rRNA 基因与最密切相关的菌株 KA5-B 的相似度≥98.7%。然而，在多糖利用方面存在差异，与菌株 KA5-B 的平均核苷酸同一性<95-96%，表明它们与 S. agariperforans KA5-B 是不同的种。为了研究与新菌株相关的细菌序列的分布，设计了一组引物并对 16S rRNA 基因进行了元分析。序列在日本各地的根际中广泛分布，但在植物和地区依赖性方面存在差异。关于表型特征，在生长温度、pH 值和优势脂肪酸方面观察到了明显的区别。SA29-B 和 YU21-B 在 15-40°C 和 pH 6.0-12 下生长，并且以 C 为主导细胞脂肪酸，而 KA5-B 在 40°C 和 pH 12 下没有生长，并且含有中等量的 C。基于这些特征，SA29-B（JCM 333368=KCTC 72223）和 YU21-B（JCM 333367=KCTC 72222）代表了 Steroidobacter 属中的新种，因此提议将其命名为 Steroidobacter agaridevorans sp. nov.。
