Microbacterium agarici sp. nov., Microbacterium humi sp. nov. and Microbacterium pseudoresistens sp. nov., isolated from the base of the mushroom Agaricus blazei

Abstract

Three Gram-positive, rod-shaped bacteria (strains CC-SBCK-209T, CC-12309T and CC-5209T) were isolated from the stalk of the edible mushroom Agaricus blazei grown in the laboratory. 16S rRNA gene sequence analysis indicated that all three isolates clearly belonged to the genus Microbacterium. Strains CC-SBCK-209T and CC-12309T were most related closely to the type strain of Microbacterium halotolerans (95.9 and 96.1 %16S rRNA gene sequence similarity, respectively). These two novel strains shared 97.9 % 16S rRNA gene sequence similarity. Levels of similarity to the type strains of all other recognized Microbacterium species were lower than 95.5 %. The third strain (CC-5209T) showed the highest 16S rRNA gene sequence similarity to the type strain of Microbacterium resistens (97.6 %); levels of similarity to the type strains of all other recognized Microbacterium species were lower than 96 %. The quinone systems of strains CC-SBCK-209T, CC-12309T and CC-5209T consisted of MK-11/MK-12, MK-11/MK-10 and MK-13 as major compounds, respectively. All three strains contained ornithine in their peptidoglycan. The major polar lipids were diphosphatidylglycerol, phosphatidylglycerol and an unknown glycolipid. The polyamine pattern consisted of spermidine and spermine as predominant components. Fatty acid profiles (anteiso-C15 : 0, iso-C16 : 0 and anteiso-C17 : 0 as major components) supported the affiliation of all three strains to the genus Microbacterium. The results of physiological and biochemical tests and DNA–DNA hybridization experiments allowed the clear phenotypic and genotypic differentiation of strains CC-SBCK-209T and CC-12309T from M. halotolerans and other closely related Microbacterium species. Strain CC-5209T could be differentiated clearly from M. resistens both genotypically and phenotypically. Based on these data, the novel strains are considered to represent three novel species of the genus Microbacterium. The names proposed for these organisms are Microbacterium agarici sp. nov. [type strain CC-SBCK-209T (=DSM 21798T=CCM 7686T)], Microbacterium humi sp. nov. [type strain CC-12309T (=DSM 21799T=CCM 7687T)] and Microbacterium pseudoresistens sp. nov. [type strain CC-5209T (=DSM 22185T=CCM 7688T)].