Abstract
We previously showed that novel filterable bacteria remain in “sterile” (<0.2 μm filtered) terrestrial environmental samples from Japan, China, and Arctic Norway. Here, we characterized the novel filterable strain IZ6T, a representative strain of a widely distributed lineage. Phylogenetic analysis showed that this strain was affiliated with the Rhizobiales (now proposed as Hyphomicrobiales) of Alphaproteobacteria, but distinct from any other type strains. Strain IZ6T shared the following chemotaxonomic features with the closest (but distantly) related type strain, Flaviflagellibacter deserti SYSU D60017T: ubiquinone-10 as the major quinone; phosphatidylethanolamine, phosphatidylcholine, and phosphatidylglycerol as major polar lipids; and slightly high G+C content of 62.2 mol%. However, the cellular fatty acid composition differed between them, and the unsaturated fatty acid (C18:1ω7c/C18:1ω6c) was predominantly found in our strain. Moreover, unlike methyrotrophs and nitrogen-fixers of the neighboring genera of Hyphomicrobiales (Rhizobiales), strain IZ6T cannot utilize a one-carbon compound (e.g., methanol) and fix atmospheric nitrogen gas. These findings were consistent with the genome-inferred physiological potential. Based on the phylogenetic, physiological, and chemotaxonomic traits, we propose that strain IZ6T represents a novel genus and species with the name Terrihabitans soli gen. nov., sp. nov. (=NBRC 106741T = NCIMB 15058T). The findings will provide deeper insight into the eco-physiology of filterable microorganisms.
Highlights
Removal of microorganisms using a micropore filter (e.g., 0.2 μm pore size) is a common procedure in research laboratories as well as medical and industrial processes [1].some bacteria in nature are known to pass through a 0.2 μm-pore-size filter and to persist in “sterile” (
Culture-independent analyses have revealed that novel and/or rarely cultivated microorganisms are present in small cell size fractions (
Note that the order Hyphomicrobiales of the class Alphaproteobacteria was recently proposed as a replacement for Rhizobiales [10] and is tentatively described as Hyphomicrobiales (Rhizobiales) in reference to previous research [11]
Summary
Removal of microorganisms using a micropore filter (e.g., 0.2 μm pore size) is a common procedure in research laboratories as well as medical and industrial processes [1]. Culturing efforts targeting filterable microorganisms have uncovered novel filterable bacteria, including obligate and facultative ultramicrobacteria as well as slender bacteria [3,5]. We obtained its phylogenetically closely-related isolates from other filtered samples (i.e., bark soil, sand, and travertine) collected in geographically remote areas such as Japan, China, and Arctic Norway [8]. These isolates formed a novel genus-level cluster in the 16S rRNA gene sequence-based phylogenetic tree [9]. Note that the order Hyphomicrobiales of the class Alphaproteobacteria was recently proposed as a replacement for Rhizobiales [10] and is tentatively described as Hyphomicrobiales (Rhizobiales) in reference to previous research [11]
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