Study On Diversity And Polyphasic Taxonomy Of Acidophilic Rare Actinomycetes From Acidic Soil

Progress in the taxonomy of the actinomycetes and acidophilic actinomycetes was introduced in this paper. The diversity of acidophilic rare Actinomycetes from acidic soil was studied and a polyphasic study was undertaken to establish the taxonomic position of three soil isolates. In this study, 252 acidophilic actinomycetes were isolated from 10 acidic soil samples collected in Jiangxi Province, Yunnan Province and Beijing with dispersion and differential centrifugation approach. About 90% of them were streptomycetes. 20 representatives of rare actinomycetes were selected by a combination of morphological feature, pH range for growth and cell wall amino acid component. They gave 11 different ARDRA patterns when digested with enzymes Bst UI and Hha I. 9 strains shared the same ARDRA pattern, which was moderately similar to the patterns of another 4 strains and distinct from those of the remaining 7 strains. On the basis of 16S rDNA sequence analysis, 18 of the 20 selected strains were assigned to 6 recognized genera. 13 of them fall within the genus Nocardia, and the other 5 strains belong to genera Agrococcus, Arthrobacter, Kitasatospora, Kocuria and Streptacidiphilus, respectively. 2 of the selected strains are members of an as-yet-unnamed novel family ("Ellin5034 group"). Our results show the good diversity of acidophilic rare actinomycetes in acidic soil, with Nocardiae predominant. On the basis of phylogenetic analyses, three isolates, strain 117,43401 and 12202 were subject to a polyphasic taxonomic study.The phylogenetic tree, based on 16S rDNA sequences, indicated that strains 117 and 43401 formed two distinct phyletic lines within the evolutionary radiation occupied by the genus Nocardia. Strain 117 and 43401 are most closely related to the type strains of Nocardia pseudobrasiliensis and Nocardia nova, sharing 16S rDNA sequence similarities of 98.2% and 98.7%, respectively. It was also evident that strain 12202 formed a distinct phyletic line with 5 strains of an as-yet-unnamed novel family ("Ellin5034 group"), sharing the highest 16S rDNA sequence similarity of 99.4%. The three isolates were readily distinguished from representatives of validly described taxa based on DNA:DNA relatedness data. Consequently strain 117 and 43401 merit recognition as two new species in the genus Nocardia. It is, therefore, proposed that the organisms be classified in this taxon as Nocardia miyunensis sp. nov. and Nocardia jiangxiensis sp. nov.; the type strains are 117T (=AS 4.1094T) and 43401T(=AS 4.1905T), respectively. Our results also suggested that strain 12202 be recognised as a new family. While more evidences are required to clarify its taxonomic position.At the same time, chemotaxonomic analyses of cell wall, mycolic acid, principal menaquinones and phospholipid type, morphological observation and physiological analyses were undertaken.