Summary auto-generated
This study describes a novel cellulolytic bacterium, Cellulosimicrobium variabile sp. nov. (strain MX5T), isolated from the hindgut of the Australian termite Mastotermes darwiniensis. The organism is a facultative anaerobe that produces both cellulolytic and xylanolytic enzymes, forming rod-shaped, V-shaped, and coccoid cells. Phylogenetic analysis of 16S rDNA sequences revealed the strain clusters with cellulolytic bacteria including Cellulosimicrobium cellulans and related species. Chemotaxonomic analysis identified key features: peptidoglycan type A4α containing lysine, absence of N-glycolylmuramic acid and mycolic acids, galactose as the major cell wall sugar, and menaquinone MK-9(H₄) as the major quinone. DNA G+C content was 70-72 mol%. The fatty acid profile, dominated by branched-chain fatty acids (ai-C15:0 at 53.6 mol%), resembled that of related Cellulosimicrobium species. Phenotypic and molecular analyses clearly differentiated this strain from other validly described Cellulosimicrobium and Cellulomonas species. The discovery contributes to understanding bacterial contributions to cellulose degradation in termite guts and extends knowledge of cellulolytic bacteria in wood-feeding insect microbiota.
Key findings
- A novel cellulolytic and xylanolytic bacterium (Cellulosimicrobium variabile sp. nov.) was isolated from the termite hindgut and shows facultative anaerobic growth with variable cell morphology
- 16S rDNA phylogenetic analysis demonstrates the strain clusters within the Cellulosimicrobium genus, with 99% similarity to strain SR272 and 97% similarity to related cellulolytic isolates
- Chemotaxonomic characterization revealed peptidoglycan type A4α with lysine, absence of glycolic and mycolic acids, galactose-rich cell walls, and MK-9(H₄) menaquinone
- Cellulosimicrobium-related strains are widespread across multiple termite species, suggesting this bacterial group is a common component of termite gut microbiota
- Clear phenotypic and molecular differentiation from C. cellulans and Cellulomonas species supports recognition as a distinct species
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Abstract
A novel cellulolytic and xylanolytic bacterium, strain MX5(T), was isolated from the hindgut contents of the Australian termite Mastotermes darwiniensis (Froggatt). The isolate was a facultative anaerobe and had a Gram-positive cell-wall profile. The rod-shaped bacterium formed irregular coryneform and coccoid cells during growth. Phylogenetic analysis of the 16S rDNA provided evidence that the organism was closely related to the as-yet undescribed cellulolytic strain SR272 and the non-validly described species 'Cellulomonas pachnodae' as well as Promicromonospora citrea and Promicromonospora sukumoe. Strain MX5(T) was assigned to the genus Cellulosimicrobium on the basis of phylogenetic and chemotaxonomic criteria. The murein of strain MX5(T) contained the diamino acid lysine. N-Glycolylmuramic acid, mycolic acids and hydroxy fatty acids were absent. The major neutral sugar in the cell wall was galactose and the major quinone was menaquinone MK-9(H(4)). The predominant fatty acids were ai-C15:0, i-C15:0, i-C16:0 and C16:0. The G+C content of the DNA was in a range 70--72 mol%. On the basis of 16S rDNA sequence similarities and chemotaxonomic features, MX5(T) was clearly different from Cellulosimicrobium cellulans and other validly described species within this phylogenetic group. For this reason, a novel species is described, for which the name Cellulosimicrobium variabile sp. nov. is proposed.