Four new Microbacterium species isolated from seaweeds and reclassification of five Microbacterium species with a proposal of Paramicrobacterium gen. nov. under a genome-based framework of the genus Microbacterium

The taxonomic relationships of 10 strains isolated from seaweeds collected from two beaches in Republic of Korea were studied by sequencing and analyses of 16S rRNA genes and whole genomes. For the construction of a more reliable and robust 16S rRNA gene phylogeny, the authentic and nearly complete 16S rRNA gene sequences of all the Microbacterium type strains were selected through pairwise comparison of the sequences contained in several public databases including the List of Prokaryotic names with Standing in Nomenclature (LPSN). The clustering of the ten study strains into five distinct groups was apparent in this single gene-based phylogenetic tree. In addition, the 16S rRNA gene sequences of a few type strains were shown to be incorrectly listed in LPSN. An overall phylogenomic clustering of the genus Microbacterium was performed with a total of 113 genomes by core genome analysis. As a result, nine major (≥ three type strains) and eight minor (two type strains) clusters were defined mostly at gene support index of 92 and mean intra-cluster OrthoANIu of >80.00%. All of the study strains were assigned to a Microbacterium liquefaciens clade and distributed further into four subclusters in the core genome-based phylogenetic tree. In vitro phenotypic assays for physiological, biochemical, and chemotaxonomic characteristics were also carried out with the ten study strains and seven closely related type strains. Comparison of the overall genomic relatedness indices (OGRI) including OrthoANIu and digital DNA-DNA hybridization supported that the study strains constituted four new species of the genus Microbacterium. In addition, some Microbacterium type strains were reclassified as members of preexisting species. Moreover, some of them were embedded in a new genus of the family Microbacteriaceae based on their distinct separation in the core genome-based phylogenetic tree and amino acid identity matrices. Based on the results here, four new species, namely, Microbacterium aurugineum sp. nov., Microbacterium croceum sp. nov., Microbacterium galbinum sp. nov., and Microbacterium sufflavum sp. nov., are described, along with the proposal of Paramicrobacterium gen. nov. containing five reclassified Microbacterium species from the "Microbacterium agarici clade", with Paramicrobacterium agarici gen. nov., comb. nov. as the type species.

Bacillus suaedae sp. nov., isolated from the stem of Suaeda aralocaspica in north-west China

A bacterial strain, designated YZJH907-2T, was isolated from the stem of Suaeda aralocaspica, collected from the southern edge of the Gurbantunggut desert, Xinjiang, PR China. Cells of strain YZJH907-2T were Gram-stain-positive, aerobic and rod-shaped. They formed white or colourless circular colonies with smooth convex surfaces. Strain YZJH907-2T grew at 4–50 °C (optimum, 28–30 °C), pH 7.0–10.0 (optimum, pH 8.0–9.0) and with 0–10 % (w/v) NaCl (optimum, 3–7 %). The genomic DNA G+C content of strain YZJH907-2T was 38.1 mol%. Phylogenetic analysis based on 16S rRNA gene sequence similarity showed that the strain was most closely related to Bacillus alcalophilus DSM 485T (97.37 %), Bacillus kiskunsagensis B16-24T (96.87 %) and Bacillus bogoriensis LBB3T (96.71 %). Average nucleotide identity values between YZJH907-2T and B. alcalophilus DSM 485Tand B. bogoriensis LBB3T were 69.2 and 69.0 %, respectively. Digital DNA–DNA hybridization values of YZJH907-2T with B. alcalophilus DSM 485T and B. bogoriensis LBB3T were 19.6 and 20.4 %, respectively. The cell wall of strain YZJH907-2T contained meso-diaminopimelic acid, and the major and secondary isoprenoid quinones were MK-7 and MK-5, respectively. Results of fatty acids showed that anteiso-C15 : 0, iso-C15 : 0 and C16 : 0 were the predominant cellular fatty acids. Two-dimensional thin-layer chromatography analysis indicated that the polar lipids included diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, three unidentified phospholipids and two unidentified glycolipids. Based on the genomic, phylogenetic and phenotypic analyses, strain YZJH907-2T represented a novel species of the genus Bacillus , and thus the name Bacillus suaedae sp. nov. is proposed. The type strain is YZJH907-2T (=CGMCC 1.18763T=KCTC 43335T).

Actinobacteria From Desert: Diversity and Biotechnological Applications

Deserts, as an unexplored extreme ecosystem, are known to harbor diverse actinobacteria with biotechnological potential. Both multidrug-resistant (MDR) pathogens and environmental issues have sharply raised the emerging demand for functional actinobacteria. From 2000 to 2021, 129 new species have been continuously reported from 35 deserts worldwide. The two largest numbers are of the members of the genera Streptomyces and Geodermatophilus, followed by other functional extremophilic strains such as alkaliphiles, halotolerant species, thermophiles, and psychrotolerant species. Improved isolation strategies for the recovery of culturable and unculturable desert actinobacteria are crucial for the exploration of their diversity and offer a better understanding of their survival mechanisms under extreme environmental stresses. The main bioprospecting processes involve isolation of target actinobacteria on selective media and incubation and selection of representatives from isolation plates for further investigations. Bioactive compounds obtained from desert actinobacteria are being continuously explored for their biotechnological potential, especially in medicine. To date, there are more than 50 novel compounds discovered from these gifted actinobacteria with potential antimicrobial activities, including anti-MDR pathogens and anti-inflammatory, antivirus, antifungal, antiallergic, antibacterial, antitumor, and cytotoxic activities. A range of plant growth-promoting abilities of the desert actinobacteria inspired great interest in their agricultural potential. In addition, several degradative, oxidative, and other functional enzymes from desert strains can be applied in the industry and the environment. This review aims to provide a comprehensive overview of desert environments as a remarkable source of diverse actinobacteria while such rich diversity offers an underexplored resource for biotechnological exploitations.

Microbacterium karelineae sp. nov. isolated from a halophyte plant in the Taklamakan desert

A bacterial strain, designated TRM 80801^T, was isolated from the Karelinea in Taklamakan desert, Xinjiang Uygur Autonomous Region, north-west China. Cells were Gram-stain-positive, aerobic, non-motile, short rods. Strain TRM 80801^T grew at 4-50 °C, with optimum growth at 28 °C, and grew at pH 6.0-11.0 and 1-15 % (w/v) NaCl. Phylogenetic analyses of the 16S rRNA gene sequences placed strain TRM 80801^T within the genus Microbacterium with the highest similarities to Microbacterium suaedae YZYP 306^T (98.97 %) and Microbacterium indicum BBH6^T (98.17 %), respectively. The DNA G+C content of TRM 80801^T is 69.38 mol%. The cell-wall peptidoglycan contained the amino acids ornithine, glutamic acid, glycine and alanine, the diagnostic diamino acid was ornithine. The acyl type of the peptidoglycan was glycolyl. Whole-cell sugars were ribose, mannose, glucose, rhamnose and galactose. The major cellular fatty acids were anteiso-C_15 : 0, anteiso-C_17 : 0 and iso-C_16 : 0. The predominant menaquinones were MK-10, MK-11 and MK-12. The polar lipids were diphosphatidylglycerol, phosphatidylglycerol. The whole-genome average nucleotide identity (ANI) value between strain TRM 80801^T and Microbacterium suaedae YZYP 306^T is 70.2 %. On the basis of the evidence presented in this study, strain TRM 80801^T is representative of a novel species in the genus Microbacterium, for which the name Microbacterium karelineae sp. nov. is proposed. The type strain is TRM 80801^T (=CCTCC AB 2019248^T=KCTC 49357^T).

Microbacterium wangchenii sp. nov., isolated from faeces of Tibetan gazelles (Procapra picticaudata) on the Qinghai-Tibet Plateau

Two strains of Gram-stain-positive, aerobic, non-spore-forming, non-motile, rod-shaped bacteria (designated dk512^T and dk508) were isolated from the faeces of Tibetan gazelle (Procapra picticaudata) collected from the Qinghai-Tibet Plateau, PR China. The 16S rRNA gene sequences of the strains showed the highest identity to Microbacterium saccharophilum K-1^T (98.0 and 97.9 % similarity, respectively). The phylogenetic analysis based on 16S rRNA gene sequences revealed that dk512^T and dk508 were members of the genus Microbacterium, and most closely related to strains Microbacterium mitrae M4-8^T and Microbacterium hatanonis FCC-01^T. The strains grew optimally on brain-heart infusion (BHI) agar with 5.0 % (v/v) sheep blood at 30 °C, pH 7.0 and with 1.0 % (w/v) NaCl. The genome of type strain dk512^T was 3.8 Mb with a G+C content of 70.6 mol%. The average nucleotide identity and digital DNA-DNA hybridization values between strain dk512^T and previously characterized Microbacterium species were <95 and <70 %, respectively. In strain dk512^T, the detected primary cellular fatty acids were anteiso-C_15 : 0 and anteiso-C_17 : 0, the main respiratory quinones were MK-9 (37.9 %) and MK-10 (35.7 %), and the polar lipids included diphosphatidylglycerol, phosphatidylglycerol and three unidentified glycolipids. The major cell-wall sugars were rhamnose, ribose and galactose. Alanine, glutamic acid, glycine and ornithine were in the cell-wall peptidoglycan. Based on phenotypic data and phylogenetic inference, these two strains represent a novel species of the genus Microbacterium, named here as Microbacterium wangchenii sp. nov, where dk512^T is designated the type strain (=CGMCC 1.16590^T=JCM 33494^T=KCTC 49313^T).