Arthrobacter deserti sp. nov., isolated from a desert soil sample

Arthrobacter horti sp. nov., isolated from mountain soil

Gram-stain-positive, aerobic, rod-shaped strains, YJM1T and YJM12S, were isolated from Maebong Mountain, Dogok-dong, Gangnam-gu, Seoul, Republic of Korea. Strains YJM1T and YJM12S exhibited growth at 5-35 °C (optimum, 20-30 °C) and pH 6-9 (optimum, pH 7) and in 0-4 % (w/v) NaCl. Strains YJM1T and YJM12S showed highest 16S rRNA gene sequence similarity to the following members of the genus Arthrobacter: A. nanjingensis A33T (98.3 %/98.2 % similarity), A. woluwensis NBRC 107840T (98.2 %/98.1 %), A. humicola KV-653T (97.3 %), A. oryzae KV-651T (97.3 %), and A. globiformis NBRC 12137T (97.2 %). The strains grew well on Reasoner's 2A, nutrient, Mueller-Hinton, yeast-dextrose, and glucose-peptone-meat extract agars. The major polar lipids of strain YJM1T were phosphatidylglycerol, diphosphatidylglycerol, and phosphatidylinositol. The primary respiratory quinone of strain YJM1T was MK-9(H2), and the major fatty acids of strains YJM1T and YJM12S were anteiso-C15 : 0, anteiso-C17 : 0, iso-C15 : 0, and iso-C16 : 0. The DNA G+C content, based on the whole genome sequence of strain YJM1T, was 68.3 mol%. Average nucleotide identity values and digital DNA-DNA hybridization values between strain YJM1T and the reference strains ranged from 75.0 to 92.7 % and from 21.0 to 65.3 %, respectively. Strain YJM1T exhibited antimicrobial activity against Bacillus subtilis and Escherichia coli. Considering the chemotaxonomic, phenotypic, genotypic, and phylogenetic results, we propose the strain YJM1T represents a novel species in the genus Arthrobacter and suggest the name Arthrobacter horti sp. nov. (type strain YJM1T=KACC 23300T=JCM 36483T).

Ecology and resistance to UV light and antibiotics of microbial communities on UV cabins in the dermatology service of a Spanish hospital

Microorganisms colonize all possible ecological habitats, including those subjected to harsh stressors such as UV radiation. Hospitals, in particular the UV cabins used in phototherapy units, constitute an environment in which microbes are intermittently subjected to UV irradiation. This selective pressure, in addition to the frequent use of antibiotics by patients, may represent a threat in the context of the increasing problem of antimicrobial resistance. In this work, a collection of microorganisms has been established in order to study the microbiota associated to the inner and outer surfaces of UV cabins and to assess their resistance to UV light and the antibiotics frequently used in the Dermatology Service of a Spanish hospital. Our results show that UV cabins harbor a relatively diverse biocenosis dominated by typically UV-resistant microorganisms commonly found in sun-irradiated environments, such as Kocuria, Micrococcus or Deinococcus spp., but also clinically relevant taxa, such as Staphylococcus or Pseudomonas spp. The UV-radiation assays revealed that, although some isolates displayed some resistance, UV is not a major factor shaping the biocenosis living on the cabins, since a similar pool of resistant microorganisms was identified on the external surface of the cabins. Interestingly, some Staphylococcus spp. displayed resistance to one or more antibiotics, although the hospital reported no cases of antibiotic-resistance infections of the patients using the cabins. Finally, no association between UV and antibiotic resistances was found.

Arthrobacter hankyongi sp. nov., Isolated From Wet Land

A Gram-staining-positive, catalase positive and oxidase negative, non-motile, non-flagellated, and oval-shaped bacterium, was designated as I2-34 ^T, isolated from wetland in Soul South Korea. Colonies were round, entire, raised, and cream colored after two days of incubation on R2A agar plates at 25 °C. Based on genomes (both 16S rRNA gene and draft genome) sequence analysis, strain I2-34 ^T belongs to the genus Arthrobacter and was most closely related to Arthrobacter deserti YIM CS25^T (98.0%). The strain I2-34 ^T had a circular genome with length of 5,186,447 base pairs (67 contigs) and 4830 total genes. Out of 4696 were protein-coding genes, 54 tRNA and 4 rRNA genes. The chemotaxonomic analysis indicates iso-C_16:0, anteiso-C_15:0, and anteiso_-C_17:0 as major fatty acids, phosphatidylglycerol (PG), diphosphatidylglycerol (DPG), and two unidentified glycolipids (GL1, GL2) as major polar lipids. The predominant quinone was MK-8(H₂). The peptidoglycan type was A3α with an. L-Lys-L-Ala interpeptide bridge. Thus, the experimental data demonstrated here show that the novel isolate shares the similar major fatty acids, major polar lipid PG, DPG, and GLs, major and major quinone MK8-(H₂) with the described members of the genus Arthrobacter. However, the low 16S rRNA gene sequence (98.0%), and some physiological and biochemical characteristics differentiate the I2-34 ^T from its closest phylogenetic neighbors. As a result, the isolate represents a novel species in within the genus Arthrobacter and family Micrococcaceae for which the name Arthrobacter hankyongi sp. nov. is proposed. The type strain is I2-34 ^T (= KACC 22217 ^T, LMG 32197 ^T).

Culturing the desert microbiota

Over the last 30 years, the description of microbial diversity has been mainly based on culture-independent approaches (metabarcoding and metagenomics) allowing an in-depth analysis of microbial diversity that no other approach allows. Bearing in mind that culture-dependent approaches cannot replace culture-independent approaches, we have improved an original method for isolating strains consisting of "culturing" grains of sand directly on Petri dishes (grain-by-grain method). This method allowed to cultivate up to 10% of the bacteria counted on the surface of grains of the three sites studied in the Great Western Erg in Algeria (Timoudi, Béni Abbès, and Taghit), knowing that on average about 10 bacterial cells colonize each grain. The diversity of culturable bacteria (collection of 290 strains) predicted by 16S rRNA gene sequencing revealed that Arthrobacter subterraneus, Arthrobacter tecti, Pseudarthrobacter phenanthrenivorans, Pseudarthrobacter psychrotolerans, and Massilia agri are the dominant species. The comparison of the culture-dependent and -independent (16S rRNA gene metabarcoding) approaches at the Timoudi site revealed 18 bacterial genera common to both approaches with a relative overestimation of the genera Arthrobacter/Pseudarthrobacter and Kocuria, and a relative underestimation of the genera Blastococcus and Domibacillus by the bacterial culturing approach. The bacterial isolates will allow further study on the mechanisms of tolerance to desiccation, especially in Pseudomonadota (Proteobacteria).

Arthrobacter polaris sp. nov., a new cold-adapted member of the family Micrococcaceae isolated from Antarctic fellfield soil

An aerobic, Gram-stain-positive and non-spore-forming strain, designated C1-1T, was isolated from a fellfield soil sample collected from frost-sorted polygons on Jane Col, Signy Island, Maritime Antarctic. Cells with a size of 0.65–0.9×1.2–1.7 µm have a flagellar motile apparatus and exhibit a rod–coccus growth cycle. Optimal growth conditions were observed at 15–20 °C, pH 7.0 and NaCl concentration up to 0.5 % (w/v) in the medium. The 16S rRNA gene sequence of C1-1T showed the highest pairwise similarity of 98.77 % to Arthrobacter glacialis NBRC 113092T. Phylogenetic trees based on the 16S rRNA and whole-genome sequences revealed that strain C1-1T belongs to the genus Arthrobacter and is most closely related to members of the ‘ Arthrobacter psychrolactophilus group’. The G+C content of genomic DNA was 58.95 mol%. The original and orthologous average nucleotide identities between strain C1-1T and A. glacialis NBRC 113092T were 77.15 % and 77.38 %, respectively. The digital DNA–DNA relatedness values between strain C1-1T and A. glacialis NBRC 113092T was 21.6 %. The polar lipid profile was composed mainly of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol and an unidentified glycolipid. The predominant cellular fatty acids were anteiso-C15 : 0 (75 %) and anteiso-C17 : 0 (15.2 %). Menaquinone MK-9(H2) (86.4 %) was the major respiratory quinone in strain C1-1T. The peptidoglycan type was determined as A3α (l-Lys–l-Ala3; A11.6). Based on all described phylogenetic, physiological and chemotaxonomic characteristics, we propose that strain C1-1T (=DSM 112353T=CCM 9148T) is the type strain of a novel species Arthrobacter polaris sp. nov.

Diversity and bioprospecting for industrial hydrolytic enzymes of microbial communities isolated from deserted areas of south-east Morocco

The current study aimed to analyze bacterial communities' diversity and abundance in three different deserted areas (Merzouga, Mhamid Elghizlane, and Erg lihoud) located in Moroccan Sahara, as well as to investigate osmotolerant microorganisms producing hydrolytic enzymes. The isolates were taxonomically affiliated using 16S rRNA gene sequencing. Four different hydrolase activities (amylase, lipase, cellulase, and protease) and osmotic stress tolerance were evaluated. The phylogenetic analysis of 364 screened isolates belonged to three phyla (Firmicutes 73%, Proteobacteria 26% and Actinobacteria 1%) and 18 different genera, from Bacillus, Ornithinibacillus, Paenibacillus, Geobacillus, Pseudomonas, Acinetobacter, Agrobacterium, Arthrobacter, Paenarthrobacter, Enterobacter, Staphylococcus, Erwinia, Herbasprillum, Ocuria, Massilia, Planomicrobium, Hodococcus, and Stenotrophomonas. The results detected a high proportion of osmotolerant and enzymes producing bacteria, many isolates can tolerate up to 55 °C (40%, 28%, and 30% in Merzouga, Mhamid Elghizlane, and Erg lihoudi, respectively). Meanwhile, the salinity tolerance reached 12% in some isolates with different proportions in each site, 29% in Merzouga, 24% in Mhamid Elghizlane, and 9% in Erg lihoudi. Furthermore, the enzymatic tests showed the presence of an amylolytic, lipolytic, cellulolytic, proteolytic activities in 20%, 31%, 63% and 72% of total strains, respectively. As a result, the present study is thus a preliminary yet critical step towards identifying the best bacterial candidates for further biotechnological applications.

Limosilactobacillus fermentum JL-3 isolated from "Jiangshui" ameliorates hyperuricemia by degrading uric acid

Recent studies into the beneficial effects of fermented foods have shown that this class of foods are effective in managing hyperuricemia and gout. In this study, the uric acid (UA) degradation ability of Limosilactobacillus fermentum JL-3 strain, isolated from "Jiangshui" (a fermented Chinese food), was investigated. In vitro results showed that JL-3 strain exhibited high degradation capacity and selectivity toward UA. After oral administration to mice for 15 days, JL-3 colonization was continuously detected in the feces of mice. The UA level in urine of mice fed with JL-3 was similar with the control group mice. And the serum UA level of the former was significantly lower (31.3%) than in the control, further confirmed the UA-lowering effect of JL-3 strain. Limosilactobacillus fermentum JL-3 strain also restored some of the inflammatory markers and oxidative stress indicators (IL-1β, MDA, CRE, blood urea nitrogen) related to hyperuricemia, while the gut microbial diversity results showed that JL-3 could regulate gut microbiota dysbiosis caused by hyperuricemia. Therefore, the probiotic Limosilactobacillus fermentum JL-3 strain is effective in lowering UA levels in mice and could be used as a therapeutic adjunct agent in treating hyperuricemia.

A Round Trip to the Desert: In situ Nanopore Sequencing Informs Targeted Bioprospecting

Bioprospecting expeditions are often performed in remote locations, in order to access previously unexplored samples. Nevertheless, the actual potential of those samples is only assessed once scientists are back in the laboratory, where a time-consuming screening must take place. This work evaluates the suitability of using Nanopore sequencing during a journey to the Tabernas Desert (Spain) for forecasting the potential of specific samples in terms of bacterial diversity and prevalence of radiation- and desiccation-resistant taxa, which were the target of the bioprospecting activities. Samples collected during the first day were analyzed through 16S rRNA gene sequencing using a mobile laboratory. Results enabled the identification of locations showing the greatest and the least potential, and a second, informed sampling was performed focusing on those sites. After finishing the expedition, a culture collection of 166 strains belonging to 50 different genera was established. Overall, Nanopore and culturing data correlated well, since samples holding a greater potential at the microbiome level also yielded a more interesting set of microbial isolates, whereas samples showing less biodiversity resulted in a reduced (and redundant) set of culturable bacteria. Thus, we anticipate that portable sequencers hold potential as key, easy-to-use tools for in situ-informed bioprospecting strategies.

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.

Nocardioides dongkuii sp. nov. and Nocardioides lijunqiniae sp. nov., isolated from faeces of Tibetan antelope (Pantholops hodgsonii) and leaves of dandelion (Taraxacum officinale), respectively, on the Qinghai-Tibet Plateau

In the present study, four bacterial strains, two (S-713^T and 406) isolated from faecal samples of Tibetan antelopes and the other two (S-531^T and 1598) from leaves of dandelion collected on the Qinghai-Tibet Plateau of PR China, were analysed using a polyphasic approach. All four isolates were aerobic, rod-shaped, non-motile, oxidase-negative, Gram-stain-positive and catalase-positive. According to four phylogenetic trees, strain pairs S-713^T/406 and S-531^T/1598 form two independent branches belonging to the genus Nocardioides, and are closest to Nocardioides lianchengensis, Nocardioides dokdonensis, Nocardioides salarius, Nocardioides marinisabuli, Nocardioides psychrotolerans and Nocardioides szechwanensis. Although sharing MK8-(H₄) as their major isoprenoid quinone, strains S-713^T and S-531^T contained C_18 : 1  ω9c (24.64 and 16.34 %) and iso-C_16 : 0 (9.74 and 29.38 %), respectively, as their main fatty acids, with remarkable differences in their biochemical profiles but only slight ones in their optimal growth conditions. The chromosomes of strains S-713^T and S-531^T were 4 207 844 bp (G+C content, 73.0 mol%) and 4 809 817 bp (G+C content, 72.5 mol%), respectively. Collectively, the two strain pairs represent two separate novel species of the genus Nocardioides, for which the names Nocardioides dongkuii sp. nov. and Nocardioides lijunqiniae sp. nov. are proposed, with S-713^T (=JCM 33698^T=CGMCC 4.7660^T) and S-531^T (=JCM 33468^T=CGMCC 4.7659^T) as the respective type strains.

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).

Arthrobacter terricola sp. nov., isolated from forest soil

A Gram-stain-positive, aerobic and rod-shaped bacterial strain, designated JH1-1^T, was isolated from a forest soil sample collected in Suwon, Gyeonggi-do, Republic of Korea. Strain JH1-1^T could grow at 10-35 °C (optimum, 28-30 °C), pH 4.5-8.5 and tolerated 5 % (w/v) NaCl. Strain JH1-1^T was most closely related to members of the genus Arthrobacter, namely Arthrobacter alkaliphilus LC6^T (98.5 % similarity), Arthrobacter methylotrophus TGA^T (98.4 %), Arthrobacter ramosus CCM 1646^T (97.8 %), Arthrobacter bambusae THG-GM18^T (97.5 %) and Arthrobacter pokkalii P3B162^T (97.3 %). The strain grew well on Reasoner's 2A agar, tryptone soya agar, nutrient agar, Mueller-Hinton agar and Luria-Bertani agar. The major polar lipid profile comprised phosphatidylglycerol, diphosphatidylglycerol, unidentified phospholipid and unidentified glycolipids. The major respiratory quinone was MK-9(H₂). The main fatty acids were C_15 : 0 anteiso, C_15 : 0 iso, C_16 : 0 iso and C_17 :0 anteiso. The DNA G+C content of the isolated strain based on the whole genome sequence was 63.6 mol%. The average nucleotide identity and digital DNA-DNA hybridization values between strain JH1-1^T and its reference type strains ranged from 81.3 to 85.4 % and from 21.1 to 29.1 %, respectively. Based on phenotypic, chemotypic and genotypic evidence, strain JH1-1^T could be differentiated phylogenetically and phenotypically from the recognized species of the genus Arthrobacter. Therefore, strain JH1-1^T is considered to represent a novel species, for which the name Arthrobacter terricola sp. nov. is proposed. The type strain is JH1-1^T (=KACC 21385^T=JCM 33641^T).

Arthrobacter mobilis sp. nov., a novel actinobacterium isolated from Cholistan desert soil

A Gram-stain-positive, aerobic, catalase-positive, oxidase-negative, non-mycelium-forming, motile, rod-shaped with one polar flagellum actinobacterium, designated E918^T, was isolated from a desert soil collected in Cholistan desert, Pakistan. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain E918^T belonged to the genus Arthrobacter and was most closely related to Arthrobacter deserti CGMCC 1.15091^T (97.2 % similarity). The peptidoglycan was of the A3α type and the whole-cell sugar profile was found to contain galactose. The major menaquinone was MK-9(H₂). The polar lipid profile consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol and two unidentified glycolipids. The major fatty acids identified were anteiso-C_15 : 0 and anteiso-C_17 : 0. The G+C content of the genomic DNA was 68.69 mol%. The digital DNA-DNA hybridization and average nucleotide identity values between strain E918^T and A. deserti CGMCC 1.15091^T were 28.0 and 83.4%, respectively. On the basis of its phylogenetic, phenotypic and chemotaxonomic features, strain E918^T was considered to represent a novel species of the genus Arthrobacter, for which the name Arthrobacter mobilis sp. nov. is proposed. The type strain of Arthrobacter mobilis is E918^T (=JCM 33392^T=CGMCC 1.16978^T).

Nocardioides jishulii sp. nov.,isolated from faeces of Tibetan gazelle (Procapra picticaudata)

Two novel Gram-stain-positive, irregular rod-shaped bacterial strains, dk3136^T and dk3543, were isolated from the faeces of Tibetan gazelle (Procapra picticaudata) in the Qinghai-Tibet Plateau of PR China. The cells were aerobic, oxidase-negative and catalase-positive. Colonies were yellowish, circular without any observable aerial mycelium after culturing at 28 ℃ for 3 days on brain-heart infusion (BHI) agar with 5 % sheep blood. The cells grew optimally at 28 °C, pH 7.5 and with 1 % (w/v) NaCl on BHI agar supplemented with 5 % sheep blood. Phylogenetic analysis of the 16S rRNA gene sequences revealed that their nearest phylogenetic relative was Nocardioides solisilvae Ka25^T (97.9 % similarity). The results of 16S rRNA gene sequence and phylogenetic/phylogenomic analyses illustrated that N. solisilvae Ka25^T, Nocardioides gilvus XZ17^T, Nocardioides houyundeii 78^T and Nocardioides daphniae D287^T were their nearest phylogenetic neighbours. The DNA G+C contents of strains dk3136^T and dk3543 were 70.3 mol% and 70.4 mol%, respectively. Their genomes exhibit lower than threshold (95-96 %) average nucleotide identity to known species of the genus Nocardioides. ll-2,6-diaminopimelic acid was the diagnostic diamino acid and MK-8(H₄) was the predominant respiratory quinone. The major polar lipids were diphosphatidylglycerol and phosphatidylglycerol. The two strains had C_18 : 1 ω9c, iso-C_16 : 0 and C_17 : 1 ω8c as the major fatty acids, and rhamnose and galactose as the main whole-cell sugars. On the basis of the results of our genotypic, phenotypic and biochemical analyses, we conclude that strains dk3136^T and dk3543 represent a novel species in genus Nocardioides, for which the name Nocardioides jishulii sp. nov. is proposed. The type strain is dk3136^T (=CGMCC 4.7570^T=JCM 33496^T=KCTC 49314^T).

Arthrobacter crusticola sp. nov., Isolated from Biological Soil Crusts in the Mu Us Sandy Land, China

Mu Us Sandy Land in China is a very fragile ecological environment due to serious desertification. While attempting to gain insights into the biodiversity of biological soil crusts of Mu Us Sandy Land, a novel bacterial strain, SLN-3^T, was isolated. It was phylogenetically placed into the genus Arthrobacter within the family Micrococcaceae based on its 16S rRNA gene sequence. The most closely related species were Arthrobacter ruber MDB1-42^T (98.6%) and Arthrobacter agilis DSM 20550^T (98.3%). Cells of the novel species were Gram-stain-positive, aerobic, and non-endospore-forming. The values of average nucleotide identity and the digital DNA-DNA hybridization between SLN-3^T and MDB1-42^T were 84.9% and 21.3%, respectively. The draft genome size of strain SLN-3^T was 3.67 Mb, and its genomic G+C content was 68.1%. The predominant cellular fatty acids were anteiso-C_15:0 and C_17:0 anteiso. Glucose, galactose, and ribose were the whole-cell sugars. The polar lipids consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol, glycolipid, and phospholipid. The peptidoglycan contained lysine, glutamic acid, and alanine. The predominant menaquinone was MK-9(H₂). Based on the data from the chemotaxonomic, phylogenetic, and phenotypic evidence, a novel species named Arthrobacter crusticola sp. nov is proposed, whose type strain is SLN-3^T (= ACCC 61595^T = JCM 33723^T).

Extreme environments: microbiology leading to specialized metabolites

The prevalence of multidrug-resistant microbial pathogens due to the continued misuse and overuse of antibiotics in agriculture and medicine is raising the prospect of a return to the preantibiotic days of medicine at the time of diminishing numbers of drug leads. The good news is that an increased understanding of the nature and extent of microbial diversity in natural habitats coupled with the application of new technologies in microbiology and chemistry is opening up new strategies in the search for new specialized products with therapeutic properties. This review explores the premise that harsh environmental conditions in extreme biomes, notably in deserts, permafrost soils and deep-sea sediments select for micro-organisms, especially actinobacteria, cyanobacteria and fungi, with the potential to synthesize new druggable molecules. There is evidence over the past decade that micro-organisms adapted to life in extreme habitats are a rich source of new specialized metabolites. Extreme habitats by their very nature tend to be fragile hence there is a need to conserve those known to be hot-spots of novel gifted micro-organisms needed to drive drug discovery campaigns and innovative biotechnology. This review also provides an overview of microbial-derived molecules and their biological activities focusing on the period from 2010 until 2018, over this time 186 novel structures were isolated from 129 representatives of microbial taxa recovered from extreme habitats.

Microbacterium ureisolvens sp. nov., isolated from a Yellow River sample

A Gram-stain positive, aerobic, non-motile and short-rod-shaped strain, CFH S00084^T, was isolated from a sediment sample of the Yellow River in Henan Province, China. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain CFH S00084^T clustered within members of Microbacterium and was most closely related to the type strains Microbacterium yannicii JCM 18959^T and Microbacterium arthrosphaerae DSM 22421^T (98.97 % and 98.36 % similarity, respectively). The strain grew optimally at 25-37 °C, at pH 7.0 and in 0-3 % (w/v) NaCl. The major whole-cell sugars were rhamnose and glucose. The cell-wall peptidoglycan mainly contained glycine, alanine and ornithine. The menaquinones of strain CFH S00084^T were MK-13, MK-12 and MK-11. The major fatty acids detected were anteiso-C15 : 0, anteiso-C17 : 0 and iso-C16 : 0. The genome of strain CFH S00084^T was 4.03 Mbp with a G+C content of 70.5 mol%. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between CFH S00084^T and the other species of the genus Microbacterium were found to be low (ANIm <85 %, ANIb <75 % and dDDH <24 %). The phylogenomic analysis provided evidence for clear phylogenetic divergence between strain CFH S00084^T and its closely related type strains. On the basis of the differential physiological properties, chemotaxonomic characteristics and low ANI and dDDH results, strain CFH S00084^T is considered to represent a novel species for which the name Microbacteriumureisolvens sp. nov. is proposed. The type strain is CFH S00084^T (=KCTC 39802^T=DSM 103157^T).

Reclassification of Arthrobacter nasiphocae (Collins et al. 2002) as Falsarthrobacter nasiphocae gen. nov., comb. nov

The original description of Arthrobacter nasiphocae M597/99/10^T demonstrated that it is distantly related to the type species of the genus Arthrobacter, Arthrobacter globiformis, and that this phylogenetic relationship is reflected by the distinct peptidoglycan type [Lys-Ala2-Gly2-3-Ala(Gly)] and the features of the quinone system, which is composed of menaquinones MK-9(H2) and MK-8(H2). Here, we report a re-evaluation of the taxonomic status of A. nasiphocae. Phylogenetically, it was observed to be only distantly related to the genus Arthrobacter and to the type species of related genera. Re-analysis confirmed the quinone system menaquinones MK-9(H2) and MK-8(H2) in A. nasiphocae. Analysis of cell polar lipids showed a profile consisting of the predominant lipids diphosphatidylglycerol, phosphatidylglycerol, dimannosylglyceride, an unidentified phospholipid and an unidentified aminophosphoglycolipid, and several minor unidentified lipids. This profile clearly is different from that of Arthrobacter species. The cell fatty acid profile also showed characteristics that distinguished A. nasiphocae from Arthrobacter species. The phylogenetic distance of A. nasiphocae from any type species of genera within the family Micrococcaceae and the distinct chemotaxonomic traits warrant the reclassification of A. nasiphocae within a novel genus, for which we propose the name Falsarthrobacter nasiphocae gen. nov., comb. nov. The type strain is M597/99/10^T (=CCUG 42953^T=CIP 107054^T=DSM 13988^T=JCM 11677^T).

Novel bacteria capable of degrading phenanthrene in activated sludge revealed by stable-isotope probing coupled with high-throughput sequencing

The indigenous microorganisms responsible for degrading phenanthrene (PHE) in activated biosludge were identified using DNA-based stable isotope probing. Besides the well-known PHE degraders Burkholderia, Ralstonia, Sinobacteraceae and Arthrobacter, we for the first time linked the taxa Paraburkholderia and Kaistobacter with in situ PHE biodegradation. Analysis of PAH-RHD_α gene detected in the heavy DNA fraction of ¹³C-PHE treatment suggested the mechanisms of horizontal gene transfer or inter-species hybridisation in PAH-RHD gene spread within the microbial community. Additionally, three cultivable PHE degraders, Microbacterium sp. PHE-1, Rhodanobacter sp. PHE-2 and Rhodococcus sp. PHE-3, were isolated from the same activated biosludge. Among them, Rhodanobacter sp. PHE-2 is the first identified strain in its genus with PHE-degrading ability. However, the involvement of these strains in PHE degradation in situ was questionable, due to their limited enrichment in the heavy DNA fraction of ¹³C-PHE treatment and lack of PAH-RHD_α gene found in these isolates. Collectively, our findings provide a deeper understanding of the diversity and functions of indigenous microbes in PHE degradation.

Chryseomicrobium deserti sp. nov., isolated from desert soil in South Korea

A Gram-stain positive, aerobic, non-motile, rod-shaped bacterium (THG-T1.18^T) was isolated from desert soil. Growth occurred at 20-35 °C (optimum 28-30 °C), at pH 5-7 (optimum 7) and at 0-4 % NaCl (optimum 0-1 %). Based on 16S rRNA sequence analysis, the nearest phylogenetic neighbours of strain THG-T1.18^T were identified as Chryseomicrobium amylolyticum DSM 23442^T (96.6 %), Chryseomicrobium imtechense JCM 16573^T (96.3 %) and Chryseomicrobium aureum KACC 17219^T (96.1 %). The polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, two unidentified aminolipids and one unidentified glycolipid. The quinone system was composed of MK-7, MK-8 and MK-6. The major fatty acids were iso C15 : 0 and anteiso C15 : 0. The type of peptidoglycan was A4β, containing of l-Orn-D-Glu. The DNA G+C content of strain THG-T1.18^T was 50.4 mol%. DNA-DNA hybridization values between strain THG-T1.18^T and C. amylolyticum DSM 23442^T, C. imtechense JCM 16573^T, C. aureum KACC 17219^T were 24.7 % (20.1 % reciprocal analysis), 19.5 % (16.1 %) and 10.4 % (6.7 %) respectively. On the basis of the phylogenetic analysis, chemotaxonomic data, physiological characteristics and DNA-DNA hybridization data, strain THG-T1.18^T represents a novel species of the genus Chryseomicrobium, for which the name Chryseomicrobium deserti sp. nov. is proposed. The type strain is THG-T1.18^T (=KACC 18929^T=CCTCC AB 2016179^T).

Microbacterium hibisci sp. nov., isolated from rhizosphere of mugunghwa (Hibiscus syriacus L.)

A Gram-stain-positive, aerobic, non-motile, short-rod shaped actinobacterium, designated THG-T2.14T, was isolated from soil sampled from the rhizosphere of mugunghwa. Growth occurred at 10-40 °C (optimum 30 °C), at pH 5.0-10.0 (optimum 7.0) and at 0-7.0 % NaCl (optimum 3.0 %). Based on 16S rRNA gene sequence analysis, the nearest phylogenetic neighbours of strain THG-T2.14T were identified as Microbacterium yannicii DSM 23203T (98.8 %), Microbacterium trichothecenolyticum DSM 8608T (98.8 %), Microbacterium arthrosphaerae DSM 22421T (98.7 %) and Microbacterium jejuense KACC 17124T (98.4 %). The major fatty acids were anteiso-C15 : 0, anteiso-C17 : 0 and iso-C16 : 0. The polar lipids were diphosphatidylglycerol, phosphatidylglycerol, one unidentified lipid, two unidentified phospholipids and two unidentified phosphoglycolipids. The menaquinones were MK-12, and MK-13. The major polyamine was spermidine. The peptidoglycan contained ornithine, alanine, glycine, homoserine and glutamic acid. The diagnostic diamino acid was ornithine. The acyl type of the muramic acid was glycolyl. The whole-cell sugars were rhamnose, ribose, galactose, arabinose, xylose and glucose. The DNA G+C content of strain THG-T2.14T was 71.2 mol%. The DNA-DNA relatedness between strain THG-T2.14T and its closest reference strains were significantly lower than the threshold value of 70 %. On the basis of the phylogenetic analysis, chemotaxonomic data, physiological characteristics and DNA-DNA hybridization data, strain THG-T2.14T represents a novel species of the genus Microbacterium, for which the name Microbacterium hibisci sp. nov. is proposed. The type strain is THG-T2.14T (=KACC 18931T=CCTCC AB 2016180T).