Methylomonas albis sp. nov. and Methylomonas fluvii sp. nov.: Two cold-adapted methanotrophs from the river Elbe and emended description of the species Methylovulum psychrotolerans

Three strains of methanotrophic bacteria (EbA(T), EbB(T) and Eb1) were isolated from the River Elbe, Germany. These Gram-negative, rod-shaped or coccoid cells contain intracytoplasmic membranes perpendicular to the cell surface. Colonies and liquid cultures appeared bright-pink. The major cellular fatty acids were 12:0 and 14:0, in addition in Eb1 the FA 16:1 omega 5(t) was also dominant. Methane and methanol were utilized as sole carbon sources by EbB(T) and Eb1, while EbA(T) could not use methanol. All strains oxidize methane using the particulate methane monooxygenase. Both strains contain an additional soluble methane monooxygenase. The strains grew optimally at 15-25 degrees C and at pH 6 and 8. Based on 16S rRNA gene analysis recovered from the full genome, the phylogenetic position of EbA(T) is robustly outside any species clade with its closest relatives being Methylomonas sp. MK1 (98.24%) and Methylomonas sp. 11b (98.11%). Its closest type strain is Methylomonas methanica NCIMB11130 (97.91%). The 16S rRNA genes of EbB(T) are highly similar to Methylomonas methanica strains with Methylomonas methanica R-45371 as the closest relative (99.87% sequence identity). However, average nucleotide identity (ANI) and digital DNA DNA-hybridization (dDDH) values reveal it as distinct species. The DNA G + C contents were 51.07 mol% and 51.5 mol% for EbA(T) and EbB(T), and 50.7 mol% for Eb1, respectively. Strains EbA(T) and EbB(T) are representing two novel species within the genus Methylomonas. For strain EbA(T) we propose the name Methylomonas albis sp. nov (LMG 29958, JCM 32282) and for EbB(T), we propose the name Methylomonas fluvii sp. nov (LMG 29959, JCM 32283). Eco-physiological descriptions for both strains are provided. Strain Eb1 (LMG 30323, JCM 32281) is a member of the species Methylovulum psychrotolerans. This genus is so far only represented by two isolates but Eb1 is the first isolate from a temperate environment; so, an emended description of the species is given. (C) 2021 The Author(s). Published by Elsevier GmbH.

Automated summary

Three strains of methanotrophic bacteria were isolated from the River Elbe in Germany, including two novel species within the genus Methylomonas and one member of the species Methylovulum psychrotolerans. These bacteria exhibit differences in carbon source utilization and growth conditions, highlighting the importance of identifying and classifying new species in this study.