Longimicrobium terrae gen. Nov., sp. Nov., an oligotrophic bacterium of the under-represented phylum gemmatimonadetes isolated through a system of miniaturized diffusion chambers

A novel chemo-organoheterotroph bacterium, strain CB-286315, was isolated from a Mediterranean forest soil sampled at the Sierra de Tejeda, Almijara and Alhama Natural Park, Spain, by using the diffusion sandwich system, a device with 384 miniature diffusion chambers. 16S rRNA gene sequence analyses identified the isolate as a member of the under-represented phylum Gemmatimonadetes, where ‘Gemmatirosa kalamazoonensis’ KBS708, Gemmatimonas aurantiaca T-27 and Gemmatimonas phototrophica AP64 were the closest relatives, with respective similarities of 84.4, 83.6 and 83.3%. Strain CB-286315 was characterized as a Gram-negative, non-motile, short to long rod-shaped bacterium. Occasionally, some cells attained an unusual length, up to 35–40 µm. The strain showed positive responses for catalase and cytochrome-c oxidase and division by binary fission, and exhibited an aerobic metabolism, showing optimal growth under normal atmospheric conditions. Strain CB-286315 was also able to grow under micro-oxic atmospheres, but not under anoxic conditions. The strain is a slowly growing bacterium able to grow under low nutrient concentrations. Major fatty acids included iso-Cω9c, summed feature 3 (Cω7c and/or iso-C 2-OH), C and iso-C.The major polar lipids were phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, two unidentified glycolipids and three phospholipids. The major isoprenoid quinone was MK-8 and the diagnostic diamino acid was meso-diaminopimelic acid. The DNA G+C content was 67.0 mol%. Based on a polyphasic taxonomic characterization, strain CB-286315 represents a novel genus and species, Longimicrobium terrae gen. nov., sp. nov., within the phylum Gemmatimonadetes. The type strain of Longimicrobium terrae is strain CB-286315 (=DSM 29007=CECT 8660). In order to classify the novel taxon within the existing taxonomic framework, the family Longimicrobiaceae fam. nov., order Longimicrobiales ord. nov. and class Longimicrobia classis nov. are also proposed.