Spatial and Temporal Shifts of Endophytic Bacteria in Conifer Seedlings of Abies religiosa (Kunth) Schltdl. & Cham

Endophytes play an important role in plant development, survival, and establishment, but their temporal dynamics in young conifer plants are still largely unknown. In this study, the bacterial community was determined by metabarcoding of the 16S rRNA gene in the rhizoplane, roots, and aerial parts of 1- and 5-month-old seedlings of natural populations of Abies religiosa (Kunth) Schltdl. & Cham. In 1-month-old seedlings, Pseudomonas dominated aerial parts (relative abundance 71.6%) and roots (37.9%). However, the roots exhibited significantly higher bacterial species richness than the aerial parts, with the dissimilarity between these plant sections mostly explained by the loss of bacterial amplification sequence variants. After 5 months, Mucilaginibacter dominated in the rhizoplane (9.0%), Streptomyces in the roots (12.2%), and Pseudomonas in the aerial parts (18.1%). The bacterial richness and community structure differed significantly between the plant sections, and these variations were explained mostly by 1-for-1 substitution. The relative abundance of putative metabolic pathways significantly differed between the plant sections at both 1 and 5 months. All the dominant bacterial genera (e.g., Pseudomonas and Burkholderia-Caballeronia-Paraburkholderia) have been reported to have plant growth-promoting capacities and/or antagonism against pathogens, but what defines their role for plant development has still to be determined. This investigation improves our understanding of the early plant-bacteria interactions essential for natural regeneration of A. religiosa forest.

Cellulomonas alba sp. nov. and Cellulomonas edaphi sp. nov., isolated from wetland soils

Two novel strains were isolated from wetland soils in Goyang, Republic of Korea. The two Gram-stain-positive, facultatively anaerobic, rod-shaped bacterial-type strains were designated MW4T and MW9T. Phylogenomic analysis based on whole-genome sequences suggested that both strains belonged to the genus Cellulomonas. The cells of strain MW4T were non-motile and grew at 20-40 °C (optimum, 35 °C), at pH 6.0-10.0 (optimum, pH 8.0) and in the presence of 0-1.0% NaCl (optimum, 0 %). The cells of strain MW9T were non-motile and grew at 20-40 °C (optimum, 35 °C), at pH 5.0-9.0 (optimum, pH 8.0) and in the presence of 0-1.0% NaCl (optimum, 0 %). The average nucleotide identity (77.1-88.1 %) and digital DNA-DNA hybridization values (21.0-34.8 %) between the two novel strains and with their closely related strains fell within the range for the genus Cellulomonas. The novel strains MW4T and MW9T and reference strains possessed alkane synthesis gene clusters (oleA, oleB, oleC and oleD). Phylogenomic, phylogenetic, average nucleotide identity, digital DNA-DNA hybridization, physiological and biochemical data indicated that the novel strains were distinct from other members of the family Cellulomonadaceae. We propose the names Cellulomonas alba sp. nov. (type strain MW4T=KACC 23260T=TBRC 17645T) and Cellulomons edaphi sp. nov. (type strain MW9T=KACC 23261T=TBRC 17646T) for the two strains.

Mucilaginibacter straminoryzae sp. nov., isolated from rice straw used for growing periphyton

A rod-shaped, non-motile, Gram-negative bacterium, strain RS28^T, was isolated from rice straw used as material for periphyton growth. Phylogenetic analysis of the 16S rRNA gene sequence revealed that strain RS28^T was affiliated with the genus Mucilaginibacter and had the highest sequence similarity to Mucilaginibacter ginkgonis HMF7856^T (96.47 %) and Mucilaginibacter polytrichastri DSM 26907^T (96.12 %). Strain RS28^T was found to grow at pH 5.5-8.0, 17-40 °C and in the presence of 0-1.5 % (w/v) NaCl. Strain RS28^T contained summed feature 3 (comprising C_16 : 1  ω7c and/or C_16 : 1  ω6c), iso-C_15 : 0 and iso-C_17 : 0 3-OH as the major fatty acids (> 10.0 %). The major polar lipids were phosphatidylethanolamine, two unidentified phospholipids, two unidentified aminophospholipids, three unidentified aminolipids and one unidentified lipid. The respiratory quinone was menaquinone 7. The genomic DNA G+C content was 44.7 mol%. Strain RS28^T possessed six putative secondary metabolite gene clusters involved in the synthesis of resorcinol, NRPS-like, terpene, lassopeptide, T3PKS and arylpolyene. On the basis of the phenotypic, chemotaxonomic, and phylogenetic characteristics, strain RS28^T represents a novel species of the genus Mucilaginibacter, for which the name Mucilaginibacter straminoryzae sp. nov. is proposed. The type strain is RS28^T (=KCTC 92039^T=LMG 32424^T).