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-BT 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-BT 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-BT. However, differences were noted in polysaccharide utilization, and average nucleotide identities were <95-96% against strain KA5-BT, indicating that they are different species from S. agariperforans KA5-BT. 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-BT and YU21-B grew at 15-40°C and pH 6.0-12 and contained C16:0 as the dominant cell fatty acid, whereas KA5-BT showed no growth at 40°C and pH 12 and contained a moderate amount of C16:0. Based on these characteristics, SA29-BT (JCM 333368T=KCTC 72223T) and YU21-B (JCM 333367=KCTC 72222) represent novel species in the genus Steroidobacter, for which the name Steroidobacter agaridevorans sp. nov. is proposed.

中文翻译：

---

琼脂降解类固醇杆菌的特征和分布。十一月，从根际土壤中分离。


由于根部分泌粘液多糖，植物根际土壤的环境不同于非根际土壤。该环境被认为是琼脂降解细菌的优先栖息地之一。在之前的一项研究中，使用根瘤菌的扩散代谢物从富含琼脂的农业土壤中分离出琼脂降解类固醇细菌 KA5-BT。基于根际中仍存在类似特征细菌的假设，利用根际土壤进行分离。从洋葱和大豆根际土壤中分离出琼脂降解性 SA29-BT 和 YU21-B。这些菌株的16S rRNA基因与关系最密切的菌株KA5-BT的同一性≥98.7%。然而，在多糖利用方面存在差异，并且针对菌株 KA5-BT 的平均核苷酸同一性<95-96%，表明它们与 S. agariperforans KA5-BT 是不同的物种。为了研究新菌株相关细菌序列的分布，设计了引物组并对 16S rRNA 基因进行了荟萃分析。序列广泛分布在日本各地的根际，但因植物和地区而异。关于表型特征，在生长温度、pH 值和主要脂肪酸方面观察到了显着特征。 SA29-BT和YU21-B在15-40°C和pH 6.0-12下生长，并含有C16:0作为主要细胞脂肪酸，而KA5-BT在40°C和pH 12下不生长，并含有适量C16:0。基于这些特征，SA29-BT (JCM 333368T=KCTC 72223T) 和 YU21-B (JCM 333367=KCTC 72222) 代表了类固醇杆菌属中的新物种，其名称为 Steroidobacter agaridevorans sp。十一月 被提议。