Dyadobacter sandarakinus sp. nov., isolated from Arctic tundra soil, and emended descriptions of Dyadobacter alkalitolerans, Dyadobacter koreensis and Dyadobacter psychrophilus

Dyadobacter chenhuakuii sp. nov., Dyadobacter chenwenxiniae sp. nov., and Dyadobacter fanqingshengii sp. nov., isolated from soil of the Qinghai-Tibetan Plateau

Six novel bacterial strains, designated CY22^T, CY357, LJ419^T, LJ53, CY399^T and CY107 were isolated from soil samples collected from the Qinghai-Tibetan Plateau, PR China. Cells were aerobic, rod-shaped, yellow-pigmented, catalase- and oxidase-positive, Gram-stain-negative, non-motile and non-spore-forming. All strains were psychrotolerant and could grow at 0 °C. The results of phylogenetic and phylogenomic analyses, based on 16S rRNA gene sequences and core genomic genes, indicated that the three strain pairs (CY22^T/CY357, LJ419^T/LJ53 and CY399^T/CY107) were closely related to members of the genus Dyadobacter and clustered tightly with two species with validly published names, Dyadobacter alkalitolerans 12116^T and Dyadobacter psychrophilus BZ26^T. Values of digital DNA-DNA hybridization between genome sequences of the isolates and other strains from the GenBank database in the genus Dyadobacter were far below the 70.0 % threshold. The genomic DNA G+C content of these six strains ranged from 45.2 to 45.8 %. The major cellular fatty acids of all six strains were iso-C_15 : 0 and summed feature 3 (comprising C_16 : 1 ω7c and/or C_16 : 1 ω6c). MK-7 was the only respiratory quinone, and phosphatidylethanolamine was the predominant polar lipid for strains CY22^T, LJ419^T and CY399^T. On the basis of the phenotypic, phylogenetic and genomic evidence presented, these six strains represent three novel members of the genus Dyadobacter, for which the names Dyadobacter chenhuakuii sp. nov., Dyadobacter chenwenxiniae sp. nov. and Dyadobacter fanqingshengii sp. nov. are proposed. The type strains are CY22^T (= GDMCC 1.3045^T = KCTC 92299^T), LJ419^T (= GDMCC 1.2872^T = JCM 33794^T) and CY399^T (= GDMCC 1.3052^T = KCTC 92306^T), respectively.

Identification and functional studies of microbial volatile organic compounds produced by Arctic flower yeasts

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.