Diversity and Antimicrobial Potential of Cultivable Endophytic Actinobacteria Associated With the Medicinal Plant Thymus roseus.

We report for the first time the isolation of endophytic actinobacteria associated with wild populations of the Chinese medicinal herb Thymus roseus Schipcz obtained from the arid land in Ili and Tacheng of the Xinjiang Province, China. Strains were isolated by special pretreatment of plant tissues and identified based on their 16S rRNA gene sequences, and their antimicrobial activities in vitro were evaluated. A total of 126 endophytic actinobacteria belonging to two classes, eight orders, 14 families, and 24 genera were isolated from different organs at the Ili and Tacheng sites. In addition, the diversity of culturable endophytic actinobacteria genera was higher at Tacheng site (n = 71, 56.35%) than the Ili site (n = 55, 43.65%). A neighbor-joining tree of 126 isolated actinobacteria showing the phylogenetic relationships based on 16S rRNA gene sequences and the genus Streptomyces was the most dominant isolate. The number of endophytic actinobacteria genera obtained from root tissues (n = 54, 42.86%) was higher compared to stem (n = 35, 27.78%) and leaf tissue (n = 37, 29.36%). Among 126 endophytic actinobacteria, 54 strains were antagonistic against at least one or more indicator organisms in vitro. Notably, most strains of Streptomyces proved antagonistic activities. For example, strain T4SB028, namely Streptomyces polyantibioticus, showed the highest inhibition ratio reached 67.06, 64.20, and 70.55% against Alternaria solani, Valsa malicola, and Valsa mali, respectively. The results demonstrate that about 30.95%, 23.01% of the tested endophytic actinobacteria were capable of producing siderophores and chitinase, respectively. Additionally, the results of the amplification of biosynthetic genes polyketide synthetase (PKS-I) and non-ribosomal peptide synthetase (NRPS) indicated that at least one antibiotic biosynthetic gene was detected in 27 (50%) of the tested strains. Our result emphasizes that the endophytic actinobacteria communities are different based on the plant tissues and the geographical environment of the sampled area. Thus, we conclude that T. roseus Schipcz. provided a rich source of endophytic actinobacteria that exhibited a broad-spectrum antimicrobial agent.

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

A Gram-staining negative, short rod, motile, light brownish-pigmented bacterial strain, designated YIM Y792(T), was isolated from a soil sample taken from Turpan desert in Xinjiang Uyghur Autonomous Region, north-western China. Phylogenetic analysis indicated that strain YIM Y792(T) belongs to the genus Delftia. Strain YIM Y792(T) shared highest 16S rRNA gene sequence similarities with Delftia lacustris DSM 21246(T) (93.96 %), Delftia tsuruhatensis NBRC 16741(T) (93.74 %), and Delftia acidovorans NBRC 14950(T) (93.62 %). Growth of the strain YIM Y792(T) was found to occur at 20-45 °C (optimum at 30 °C), pH 6.0-9.0 (optimum at pH 7.0), and salinities of 0-3.0 % NaCl (optimum at 1.0 %). The new bacterium exhibits typical chemotaxonomic features of the genus Delftia with ubiqinone-8 (Q-8) as the predominant quinone and C16:0, Summed feature 3, Summed Feature 8 as major fatty acids (>10 %). The polar lipids were found to consist of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, glycolipid, two unidentified phospholipids and one unidentified lipid. The G+C content of the genomic DNA of strain YIM Y792(T) was found to be 70.3 mol%. The DNA-DNA relatedness values between strain YIM Y792(T) and D. lacustris DSM 21246(T), D. tsuruhatensis NBRC16741(T), D. acidovorans NBRC14950(T) were 35.5 ± 2.0, 17.1 ± 1.8, 26.2 ± 2.0 %. Based on the phylogenetic, chemotaxonomic and phenotypic data presented here, we propose a novel species with the name Delftia desertisoli sp. nov. The type strain is YIM Y792(T) (=KCTC 42377(T) = JCM 30639(T)).

Rhizobium tarimense sp. nov., isolated from soil in the ancient Khiyik River.

A Gram-negative, non-motile, pale-yellow, rod-shaped bacterial strain, PL-41(T), was isolated from Populus euphratica forest soil at the ancient Khiyik River valley in Xinjiang Uyghur Autonomous Region, People's Republic of China. Strain PL-41(T) grew optimally at 30 °C and pH 7.0-8.0. The major quinone was Q-10. The predominant cellular fatty acids of strain PL-41(T) were summed feature 8 (comprising C18 : 1ω7c and C18 : 1ω6c), C16 : 0 and C19 : 0 cyclo ω8c. Polar lipids of strain PL-41(T) include two unidentified aminophospholipids (APL1, 2), two unidentified phospholipids (PL1, 2), phosphatidylcholine and three unidentified lipids (L1-3). Strain PL-41(T) showed 16S rRNA gene sequence similarity of 97.0-97.5 % to the type strains of recognized species of the genus Rhizobium. Phylogenetic analysis of strain PL-41(T) based on the sequences of housekeeping genes recA and atpD confirmed (similarities are less than 90 %) its position as a distinct species of the genus Rhizobium. The DNA G+C content was 57.8 mol%. DNA-DNA relatedness between strain PL-41(T) and the type strains of Rhizobium huautlense S02(T), Rhizobium alkalisoli CCBAU 01393(T), Rhizobium vignae CCBAU 05176(T) and Rhizobium loessense CCBAU 7190B(T) were 33.4, 22.6, 25.5 and 45.1 %, respectively, indicating that strain PL-41(T) was distinct from them genetically. Strain PL-41(T) also can be differentiated from these four phylogenetically related species of the genus Rhizobium by various phenotypic properties. On the basis of phenotypic properties, phylogenetic distinctiveness and genetic data, strain PL-41(T) is considered to represent a novel species of the genus Rhizobium, for which the name Rhizobium tarimense sp. nov. is proposed. The type strain is PL-41(T) ( = CCTCC AB 2011011(T) = NRRL B-59556(T)).