A Taxonomic Study of Thermomonospora and Other Monosporic Actinomycetes

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Abstract
SUMMARY: A large collection of Thermomonospora isolates and type or reference cultures, together with representatives of the genera Thermoactinomyces, Saccharomonospora, Micropolyspora and Actinomadura, were included in a numerical taxonomic study. The 113 strains were examined for 101 morphological, physiological and biochemical characters and data were analysed using simple matching (SSM ), Jaccard (SJ ) and pattern difference (DP ) coefficients with clustering by both single and unweighted pair group average algorithms. All of the analyses produced similar classifications which were little affected by test error, estimated at 1.1%. Thermomonospora strains formed two major clusters identified as “Thm. chromogena” and the white Thermomonospora group, respectively, while type strains of “Acm. flexuosa”, Mip. faeni and Thm. mesophila were well separated from one another and all major clusters. The low phenetic similarity between the two Thermomonospora clusters supports suggestions based on chemical data that “Thm. chromogena” may be better classified in a separate genus. Three subclusters were detected within the white Thermomonospora group and equated with the species “Thm. fusca”, Thm. curvata and Thm. alba. The Saccharomonospora cluster was heterogeneous and, although it included strains identified as Sam. viridis, “Mip. caesia” and Thermomonospora sp. (lilac), species could not be distinguished. The type strain of “Thm. galeriensis” shared the distinguishing characteristics of this cluster and should be regarded as a member of the genus Saccharomonospora. Only five strains of Thermoactinomyces were included, but they formed a cluster with an internal structure which supported a previous numerical classification of species in this genus. Wall chemotype and spore heat-resistance properties were consistent with generic identification. As a result of this study, five Thermomonospora spp. are recognized: “Thm. chromogena” comb. nov. nom. rev. (synonyms “Actinobifida chromogena”, “Thm. falcata”); Thm. mesophila; “Thm. fusca” sp. nov. nom. rev.; Thm. alba (synonym Thm. mesouviformis); Thm. curvata. The experimental data allowed the development of an identification scheme for these species and also provided tests to confirm generic identifications of other thermophilic actinomycete isolates.

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