Diverse biofilm-forming Sphingomonadaceae represent twelve novel species isolated from glaciers on the Tibetan Plateau.

Abstract

The family Sphingomonadaceae, encompassing the genus Sphingomonas and related taxa, comprises diverse Gram-negative, aerobic, rod-shaped bacteria found in varied habitats, including air, soil, water and glaciers. Recent genomic-based taxonomic revisions have reclassified some Sphingomonas species into new genera, such as Parasphingomonas and Alteristakelama, due to polyphyletic relationships within the family Sphingomonadaceae. Certain Sphingomonadaceae species are known for forming biofilms or functioning as aerobic anoxygenic phototrophic bacteria, traits that enhance resilience in extreme environments like the cryosphere. In this study, we isolated 12 novel strains from Tibetan Plateau glaciers, revealing significant phenotypic and genotypic diversity. Based on phylogenomic analyses, six strains were classified within Sphingomonas, five within Parasphingomonas and one within Alteristakelama. These strains exhibit broad pH (4-11), salt tolerance (0-3.0%) and temperature adaptability (0-37 °C), alongside varied metabolic capabilities, including diverse carbon source utilization and enzyme activities. Eleven strains exhibit biofilm formation, and some possess genes for carotenoid biosynthesis and photosynthesis. The 16S rRNA gene sequence similarities with their closest relatives ranged from 97.6% to 99.9%, while the average nt identity and digital DNA-DNA hybridization values between these strains and known species with validly published names were below 89.80% and 36.60%, respectively. Polyphasic analyses, encompassing phylogenetic, phenotypic and genotypic analyses, confirm that these strains represent 12 novel species within the family Sphingomonadaceae. We propose the following names: Alteristakelama amylovorans sp. nov., Sphingomonas sorbitolis sp. nov., Sphingomonas fucosidasi sp. nov., Sphingomonas sandaracina sp. nov., Sphingomonas rhamnosi sp. nov., Sphingomonas arabinosi sp. nov., Sphingomonas flavida sp. nov., Parasphingomonas frigoris sp. nov., Parasphingomonas halimpatiens sp. nov., Parasphingomonas zepuensis sp. nov., Parasphingomonas caseinilytica sp. nov. and Parasphingomonas puruogangriensis sp. nov. This study enhances our understanding of Sphingomonadales diversity and its ecological adaptations in extreme environments.