Strain Q3-56T, isolated from Arctic tundra soil, was found to be a Gram-stain-negative, yellow-pigmented, oxidase- and catalase-positive, non-motile, non-spore-forming, rod-shaped and aerobic bacterium. Strain Q3-56T grew optimally at pH 7.0 and 28 °C. The strain could tolerate up to 1 % (w/v) NaCl with optimum growth in the absence of NaCl. The strain was not sensitive to oxacillin and ceftazidime. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain Q3-56T belonged to the genus Dyadobacter . Strain Q3-56T showed the highest sequence similarities to Dyadobacter luticola T17T (96.58 %), Dyadobacter ginsengisoli Gsoil 043T (96.50 %), Dyadobacter flavalbus NS28T (96.43 %) and Dyadobacter bucti QTA69T (96.43 %). The predominant respiratory isoprenoid quinone was identified as MK-7, The polar lipid profile of strain Q3-56T was found to contain one phosphatidylethanolamine, three unidentified aminolipids, three unidentified lipids and one unidentified phospholipid. The G+C content of the genomic DNA was determined to be 49.1 mol%. The main fatty acids were summed feature 3 (comprising C16 : 1  ω7c/C16 : 1  ω6c), iso-C15 : 0, C16 : 1  ω5c and iso-C16 : 1 3-OH. On the basis of the evidence presented in this study, a novel species of the genus Dyadobacter , Dyadobacter sandarakinus sp. nov., is proposed, with the type strain Q3-56T (=CCTCC AB 2019271T=KCTC 72739T). Emended descriptions of Dyadobacter alkalitolerans , Dyadobacter koreensis and Dyadobacter psychrophilus are also provided.

According to average nucleotide identity (ANI) analysis of the complete genomes, strain 24S4–2 isolated from Antarctica is considered as a potential novel Arthrobacter species. Arthrobacter sp. 24S4–2 could grow and produce ammonium in nitrate or nitrite or even nitrogen free medium. Strain 24S4–2 was discovered to accumulate nitrate/nitrite and subsequently convert nitrate to nitrite intracellularly when incubated in a nitrate/nitrite medium. In nitrogen-free medium, strain 24S4–2 not only reduced the accumulated nitrite for growth, but also secreted ammonia to the extracellular under aerobic condition, which was thought to be linked to nitrite reductase genes nirB, nirD, and nasA by the transcriptome and RT-qPCR analysis. A membrane-like vesicle structure was detected in the cell of strain 24S4–2 by transmission electron microscopy, which was thought to be the site of intracellular nitrogen supply accumulation and conversion. This spatial and temporal conversion process of nitrogen source helps the strain maintain development in the absence of nitrogen supply or a harsh environment, which is part of its adaption strategy to the Antarctic environment. This process may also play an important ecological role, that other bacteria in the environment would benefit from its extracellular nitrogen source secretion and nitrite consumption characteristics.

Microbial volatile organic compounds (mVOCs) can serve as a communication channel among microorganisms, insects and plants, making them important in ecosystem. In order to understand the possible role of mVOCs in Arctic ecology, the microbes in Arctic flowers and their mVOCs and effects on plants were investigated. This study aims to isolate different yeast species from the flowers of five Arctic plant species and further to explore the function of mVOCs emitted by these microbes to plant. It was found that the composition and amount of mVOCs produced by the isolated yeasts were considerably affected by changes in incubation temperature. When the incubation temperature rose, the species of alcohols, aldehydes, esters, organic acids, and ketones increased, but substances specific to low temperature decreased or disappeared. When yeasts were co-cultured with Arabidopsis thaliana without any direct contact, mVOCs produced by the isolated yeasts inhibited the seed germination of A. thaliana at low temperatures; however, the mVOCs promoted the chlorophyll content, fresh weight, root weight and flowering rate of Arabidopsis plants. Although the overall growth-promoting effect of yeast mVOCs was higher at 20°C than at 10°C, the growth-promoting effect on roots, flowers and chlorophyll was highest at 10°C. When cultured at 10°C, the mVOCs produced by Cystofilobasidium capitatum A37, Cryptococcus sp. D41, and Sporidiobolus salmonicolor D27 had the highest growth-promoting effects on the root, flowering rate and chlorophyll content of Arabidopsis, respectively. In the co-culture system, some new mVOCs were detected, such as hendecane, tetradecane, and 1-hexanol that have been proven to promote plant growth. In addition, mVOCs of the isolated Arctic yeasts could inhibit the growth of several microorganisms, especially filamentous fungi. It was the first time to prove that mVOCs produced by the isolated yeasts had varying effects on plant growth at different incubating temperatures, providing a reference for the interactions between microorganisms and plants and their possible responses to climate change in the Arctic area. Moreover, the characteristics of promoting plant growth and inhibiting microbial growth by mVOCs of Arctic yeasts would lay a foundation for potential applications in the future.

A Gram-negative, non-motile, aerobic bacterium, named 02-257T, was isolated from Antarctic soil. The cells are surrounded by relatively thin capsules and were catalase-positive and oxidase-negative cocci. Growth of strain 02-257T was observed at 4–35 °C (optimum, 28–30 °C), pH 6.0–8.0 (optimum, pH 6.0) and with 0–1.5% NaCl (optimum, 0 %). Strain 02–257 showed the highest 16S rRNA gene sequence similarity to Paraconexibacter algicola Seoho-28T (95.06 %). Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain 02-257T is a member of a novel species belonging to the clade formed by members of the genus Paraconexibacter in the family Paraconexibacteraceae . The DNA G+C content was 72.9 mol%. Strain 02-257T contained C16 : 0-iso (23.0 %), C18  :  1 ω9c (13.8 %), C16 : 0 (12.5 %) and C17 : 1 ω9c-iso (10.8 %) as major cellular fatty acids and menaquinone MK-7(H4) was detected as the only isoprenoid quinone. Diphosphatidylglycerol, phosphatidylinositol, phosphatidylinositole mannoside, phosphatidylinositole dimannoside, unidentified phosphoglycolipid, unidentified aminophospholipid, two unidentified phospholipids, three unidentified aminolipids and six unidentified lipids were the major polar lipids. meso-Diaminopimelic acids were the diagnostic diamino acids in the cell-wall peptidoglycan. On the basis of phenotypic, chemotaxonomic and phylogenetic data, strain 02-257T is considered to represent a novel species of the genus Paraconexibacter , for which the name Paraconexibacter antarcticus sp. nov. is proposed. The type strain is 02-257T (=CCTCC AB 2021030T=KCTC 49619T).

A rod-shaped, Gram-stain-negative, non-motile and aerobic bacterium, designated Q8-18T, was isolated from soil of glacier foreland in Austre Lovénbreen, Arctic, and subjected to a polyphasic taxonomic study. Strain Q8-18T grew optimally at 20 °C, pH 5.0–8.0 and in the presence of 0–1.0 % (w/v) NaCl. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain Q8-18T belonged to the family Sphingobacteriaceae . Strain Q8-18T showed the highest sequence similarity to Pedobacter mendelii CCM 8685T (96.8%), Pedobacter lithocola CCM 8691T (96.8%), Pedobacter roseus CL-GP80T (96.7%), Pedobacter changchengzhani E01020T (96.7%), Pedobacter alluvionis DSM 19624T (96.6%), Pedobacter jejuensis THG-DR3T (96.3%), Pedobacter ginsengiterrae DCY49T (95.9%) and Pedobacter jamesrossensis CCM 8689T (95.9%). A whole genome-level comparison of strain Q8-18T with P. roseus CL-GP80T, P. changchengzhani E01020T, P. alluvionis DSM 19624T and Pedobacter heparinus LMG 10339T revealed average nucleotide identity values of 77.0, 76.0, 77.0 and 70.4%, respectively. The only respiratory isoprenoid quinone was menaquinone-7. The polar lipid profile of strain Q8-18T was found to contain one phosphatidylethanolamine, eight unidentified aminolipids, one aminophospholipids and five unidentified lipids. The G+C content of the genomic DNA was determined to be 35.4 mol%. The main fatty acids were summed feature 3 (comprising C16 : 1  ω7c and/or C16 : 1  ω6c), iso-C15 : 0 and anteiso-C15 : 0. On the basis of the evidence presented in this study, a novel species of the genus Pedobacter , Pedobacter mucosus sp. nov., is proposed, with the type strain Q8-18T (=CCTCC AB 2020009T=KCTC 82636T).