Strains YM18-098T and A5E-52T were both Gram-positive, aerobic, irregular rod-shaped bacteria, with lysine and ornithine as the diagnostic diamino acids of their peptidoglycans, respectively. The acyl type of the peptidoglycan in both cases was N-glycolyl. The major menaquinones were MK-11, -12 and -13. Mycolic acids were not detected. The G+C content of the DNA was 69–70 mol%. Comparative 16S rRNA studies revealed that the isolates belonged to the genus Microbacterium, that YM18-098T was closely related to the species Microbacterium lacticum and Microbacterium schleiferi, and that A5E-52T was closely related to the species Microbacterium aurum, Microbacterium aoyamense, Microbacterium deminutum and Microbacterium pumilum. DNA-DNA relatedness analysis showed that the isolated strains represented two separate genomic species. Based on both phenotypic and genotypic data, the following new species of the genus Microbacterium are proposed: Microbacterium flavum sp. nov. and Microbacterium lacus sp. nov., with the type strains YM18-098T (= MBIC08278T, DSM 18909T) and A5E-52T (= MBIC08279T, DSM 18910T), respectively.
Totally 192 actinomycetes colonies were isolated from 18 marine sediment samples of Palk Strait region of Bay of Bengal, India. Among them, 68 isolates were morphologically distinct on the basis of colour of spore mass, reverse side colour, aerial and substrate mycelia formation, production of diffusible pigment and sporophore morphology. Thirty-nine isolates were assigned to the genus Streptomyces, Actinopolyspora (10), Saccharopolyspora (7), Actinomadura (4), Nocardiopsis (3), Micromonospora (2), Actinomyces (1), Actinoplanes (1) and Microbispora (1). From these, 64 isolates with aerial mycelia, 65 isolates with substrate mycelia and 61 isolates had both aerial and substrate mycelia.
Diverse rhizoplane streptomycetes with high levels of anti-phytopathogenic activity were efficiently isolated from healthy herbaceous plants using a new enrichment method, which we designated as the moist incubation and desiccation (MI&D) method. The MI&D method involves incubating root tissues on humic acid-vitamin (HV) agar, desiccating roots bearing arthrospore chains of colonized streptomycetes in dried soil particles, then liberating spores by agitation in water. Dilutions of the liquid enriched with streptomycete spores are then plated and incubated on HV agar. The desiccation stage drastically reduces bacterial contamination, thereby achieving selective isolation of streptomycetes.