Different factors drive the assembly of pine and Panax notoginseng-associated microbiomes in Panax notoginseng-pine agroforestry systems

Land-use conversion affects the composition and assembly of plant-associated microbiomes, which in turn affects plant growth, development, and ecosystem functioning. However, agroforestry systems, as sustainable land types, have received little attention regarding the dynamics of different plant-associated microbes. In this study, we used high-throughput sequencing technology to analyze the assembly mechanisms and the driving factors of pine- and Panax notoginseng (P.n.)-associated microbiomes during the conversion of different pine forests (Pinus kesiya var. langbianensis and Pinus armandii) into P.n.-pine agroforestry systems. The results showed that the conversion of pure pine forest into P.n.-pine agroforestry systems significantly altered the diversity of pine-associated fungi rather than the community structure, and the community structure of P.n.-associated fungi rather than the diversity. Additionally, plant-associated fungi were more responsive to land-use change than bacteria. Main effect analysis revealed that compartment rather than genotype was the driving factor of pine- and P.n.-associated microbiomes, but P.n. cultivation also significantly affected the assembly of pine-associated microbiomes. In addition, there was a transfer of P.n. endophytes to pine trees in agroforestry systems and the beneficial microbiomes (Massilia, Marmoricola, Herbaspirillum, etc.) were enlarged in pine roots. Therefore, the diversity of the assembly mechanisms of P.n.- and pine-associated microbiomes played an important role in the P.n.--pine agroforestry systems and were the basis for the sustainable development of the P.n.--pine agroforestry systems.

Biotransformation of Ginsenoside Rb1 to Ginsenoside CK by Strain XD101: a Safe Bioconversion Strategy

Ginsenoside Rb1 is the main predominant component in Panax species. In this study, an eco-friendly and convenient preparation method for ginsenoside CK has been established, and five strains of β-glucosidase-producing microorganisms were screened out from the soil of a Panax notoginseng planting field using Esculin-R2A agar. Aspergillus niger XD101 showed that it has excellent biocatalytic activity for ginsenosides; one of the isolates can convert ginsenoside Rb1 to CK using extracellular enzyme from the mycelium. Mycelia of A. niger were cultivated in wheat bran media at 30 °C for 11 days. By the removal of mycelia from cultured broth, enzyme salt fractionation by ammonium sulfate (70%, v/v) precipitation, and dialysis, sequentially, crude enzyme preparations from fermentation liquid supernatant were obtained. The enzymatic transformed Rb1 as the following pathways: Rb1→Rd→F2→CK. The optimized reaction conditions are at reaction time of 72 h, in the range of pH 4-5, and temperature of 50-60 °C. Active minor ginsenosides can be obtained by a specific bioconversion via A. niger XD101 producing the ginsenoside-hydrolyzing β-glucosidase. In addition, the crude enzyme can be resulted in producing ginsenoside CK via conversion of ginsenoside Rb1 at high conversion yield (94.4%). FDA generally regarded, A.niger as safe microorganism. Therefore, these results indicate that A. niger XD10 may provide an alternative method to prepare ginsenoside CK without food safety issues in the pharmaceutical industry.

Mucilaginibacter inviolabilis sp. nov., isolated from the phycosphere of Haematococcus lacustris NIES 144 culture

A Gram-stain-negative, non-motile, rod-shaped, aerobic bacterial strain, designated HC2^T, was isolated from the phycosphere of Haematococcus lacustris NIES 144 culture. Strain HC2^T was able to grow at pH 4.5-8.0, at 4-32 °C and in the presence of 0-2 % (w/v) NaCl. Phylogenetic analysis of the 16S rRNA gene sequence revealed that strain HC2^T was affiliated to the genus Mucilaginibacter and shared the highest sequence similarity with Mucilaginibacter lappiensis ANJKI2^T (98.20 %) and Mucilaginibacter sabulilitoris SMS-12^T (98.06 %). Strain HC2^T contained summed feature 3 (C_16 : 1 ω7c and/or C_16 : 1 ω6c) and iso-C_15 : 0 as the major fatty acids (>10.0 %). The major polar lipids were phosphatidylethanolamine, one unidentified aminophospholipid, one unidentified phospholipid, two unidentified aminolipids and four unidentified lipids. The respiratory quinone was menaquinone 7 (MK-7). The genomic DNA G+C content was 42.0 %. On the basis of the phenotypic, chemotaxonomic and phylogenetic characteristics, strain HC2^T represents a novel species of the genus Mucilaginibacter, for which the name Mucilaginibacter inviolabilis sp. nov. is proposed. The type strain is HC2^T (=KCTC 82084^T=JCM 34116^T).

Mucilaginibacter terrenus sp. nov., isolated from manganese mine soil

Strain ZH6^T is a Gram-stain-negative, rod-shaped, aerobic bacterium isolated from manganese mine soil. Strain ZH6^T had highest 16S rRNA gene sequence similarities to Mucilaginibacter yixingensis YX-36^T (96.9 %) and Mucilaginibacter psychrotolerans NH7-4^T (96.8 %). The genome size of strain ZH6^T was 4.61 Mb with a DNA G+C content of 44.0 mol%. The average nucleotide identity and digital DNA-DNA hybridization values between strain ZH6^T and M. yixingensis DSM 26809^T were 70.6 and 19.2 %, respectively. Strain ZH6^T had menaquinone-7 as a major quinone and main cellular fatty acids of iso-C_15 : 0, iso-C_17 : 0 3-OH and summed feature 3 (C_16 : 1ω7c and/or C_16 : 1ω6c). The polar lipids of strain ZH6^T were a phosphatidylethanolamine, an unidentified glycolipid, an unidentified phospholipid, three unidentified aminophospholipids and four unidentified lipids. Based on the phenotypic, chemotaxonomic and phylogenetic results, strain ZH6^T represents a novel species of the genus Mucilaginibacter, for which the name Mucilaginibacterterrenus sp. nov., is proposed. The type strain is ZH6^T (=CCTCC AB 2018373^T=KCTC 72075^T).

Mucilaginibacter endophyticus sp. nov., an endophytic polysaccharide-producing bacterium isolated from a stem of Miscanthus sinensis

In this study, a Gram-negative, rod-shaped, endophytic bacterial strain (RS1^T) capable of producing large amounts of exopolysaccharides was isolated from a stem of Miscanthus sinensis. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain RS1^T is closely related to Mucilaginibacter kameinonensis NBRC 102645^T (98.72%), followed by Mucilaginibacter gossypiicola Gh-48^T (97.56%) and Mucilaginibacter oryzae DSM 19975^T (97.36%). The DNA G + C content of strain RS1^T was determined to be 42.80 mol%. ANIb and GGDC values from genomic comparison between the genomes of strain RS1^T and the related reference species were less than 95% and 70%, respectively. The major cellular fatty acids (more than 10% of total fatty acids) were identified as iso-C15: 0, C16:0, iso-C17:0-3OH and summed feature 3 (C16: 1ω7c and/or iso-C15:02-OH). The only isoprenoid quinone detected was MK-7. Based on the physiological, genotypic and genomic characteristics, strain RS1^T is concluded to represent a novel species of the genus Mucilaginibacter, for which the name Mucilaginibacter endophyticus sp. nov. is proposed (type strain RS1^T = KCTC 62785^T = GDMCC 1.1414^T).