Flavisolibacter nicotianae sp. nov., isolated from rhizosphere soil of Nicotiana tabacum L

Biochar amendment reduces cadmium uptake by stimulating cadmium-resistant PGPR in tomato rhizosphere

Biochar amendment in the soil can exert a positive effect in reducing heavy metal toxicity in plants. However, it remains unclear the extent to which this effect is associated with the modulation of plant growth-promoting rhizobacteria (PGPR). Here, we initially conducted a pot experiment using tomato (Solanum lycopersicum L.) as a model plant grown in soil spiked with cadmium. First, we found biochar amendment to result in reduced cadmium uptake in tomato plants and trackable changes in the tomato rhizosphere microbiome. Then, a rhizosphere transplant experiment validated the importance of this microbiome modulation for cadmium-toxicity amelioration. Sequence-based analyses targeted the isolation of representative isolates of PGPR, including Bacillus and Flavisolibacter spp. that displayed in vitro cadmium tolerance and biosorption capabilities (in addition to abilities to solubilize phosphate and produce indole acetic acid). Last, we performed a soil inoculation experiment and confirmed the effectiveness of these isolates in reducing cadmium toxicity in tomato plants. Besides, we found the inoculation of these taxa as single inoculant and in combination to result in increased activities of specific antioxidant enzymes in tomato tissues. Taken together, this study revealed the ecological and physiological mechanisms by which biochar amendment indirectly alleviate cadmium toxicity in tomato plants, in this case, via the modulation and activity of specific PGPR populations. This study provides new insights into strategies able to promote beneficial PGPR in the rhizosphere with potential application to ameliorate heavy metal toxicity in plants.

Targeted metagenome sequencing reveals the abundance of Planctomycetes and Bacteroidetes in the rhizosphere of pomegranate

Agricultural productivity of pomegranate can be enhanced by identifying the crop-associated microbial diversity in the rhizosphere region with respect to plant growth promoters and other beneficial organisms. Traditional culture methods have limitations in microbial screening as only 1-2% of these organisms can be cultured. In the present study, 16S rRNA amplicon-based metagenomics approach using MinION Oxford Nanopore platform was employed to explore the microbial diversity in the rhizosphere of pomegranate Bhagwa variety, across variable soil depths from 0 to 5 cms (R2), 5-10 cms (R4) and 10-15 cms (R6), using bulk soil as the control. Across all the three layers, significant variations in pH, nitrogen content and total fungal count were observed. 16S rRNA analysis showed the abundance of planctomycetes, Pirellula staleyi, followed by bacteroidetes, Flavisolibacter LC59 and Niastella koreensis across the various soil depths in the rhizospheric soil samples. Pathway prediction analysis indicated arginine and proline metabolism (gamma-glutamyl putrescine oxidase) and hydrogen sulfide biosynthesis as the most abundant pathway hits. Comparative abundance analysis across layers showed the R6 layer with the maximum microbial diversity in terms of highest dimension of variation (79.2%) followed by R4 and R2 layers (p < 0.01). Our analysis shows the significant influence of root zone in shaping microbial diversity. This study has reported the presence of Planctomycetes, Pirellula staleyi for the first time in the pomegranate field.

Hanamia caeni gen. nov., sp. nov., a Member of the Family Chitinophagaceae Isolated from Activated Sludge in Korea

A novel Gram-stain-negative, aerobic, yellowish-pigmented, non-motile, rod-shaped bacterial strain, designated strain BO-59^T, was isolated from the activated sludge of a wastewater treatment plant in Hanam City, South Korea. Phylogenetic study based on the 16S rRNA gene sequence positioned BO-59^T in a distinct lineage in the family Chitinophagaceae, sharing less than 92.8% sequence similarity with members of the closely related genera Ferruginibacter, Flavitalea, Pseudoflavitalea, Flavisolibacter, Niastella, and Terrimonas. Phylogenomic- and genomic relatedness analyses revealed that strain BO-59^T is clearly distinguished from other genera in the family Chitinophagaceae by average nucleotide identity < 66.9%) and the genome-to-genome distance (< 29.5%) values. The strain BO-59^T contained MK-7 as the predominant quinone, and iso-C_15:0, iso-C_17:0 3OH, and iso-C_15:1 G as major fatty acids (> 10%). The DNA G + C content was 39.1 mol% based on genome sequence analysis. The polar lipids of strain BO-59^T were phosphatidylethanolamine, an unidentified aminophospholipid and three unidentified polar lipids. 16S rRNA gene sequence similarity, physiological, and biochemical characteristics indicated that strain BO-59^T represents a novel species of a new genus, for which the name Hanamia caeni gen. nov., sp. nov. is proposed. The type strain is BO-59^T (= KACC 19646^T = LMG 30865 ^T).

Hymenobacter negativus sp. nov., bacteria isolated from mountain soil collected in South Korea

Two novel Gram-negative bacterial strains BT442^T and BT584 were isolated from dry soil collected in mountains Busan and Guri, Korea during wintertime. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strains BT442^T and BT584 both belong to a distinct lineage within the genus Hymenobacter (family Hymenobacteraceae, order Cytophagales, class Cytophagia). Strain BT442^T was closely related to Hymenobacter soli PB17^T (98.0% 16S rRNA gene similarity) and Hymenobacter terrae POA9^T (97.6%). No other recognized bacterial species showed more than 97% 16S rRNA gene sequence similarity to strains BT442^T. The genome size of strain BT442^T was 5,143,362 bp. Bacterial growth was observed at 10-30 °C (optimum 25 °C), pH 6.0-8.0 (optimum pH 6.0) in R2A agar and in the presence up to 1% NaCl. The major cellular fatty acids of strains BT442^T and BT584 were iso-C_15:0, anteiso-C_15:0 and summed feature 3 (C_16:1 ω6c / C_16:1 ω7c). In addition, their predominant respiratory quinone was MK-7. The major polar lipids of strains BT442^T and BT584 were identified to be phosphatidylethanolamine, aminophospholipid, and aminolipid. Based on the biochemical, chemotaxonomic, and phylogenetic analyses, strains BT442^T and BT584 are novel bacterial species within the genus Hymenobacter, and the proposed name is Hymenobacter negativus. The strain type of Hymenobacter negativus is BT442^T (= KCTC 72902^T = NBRC XXXX^T).

Flavisolibacter longurius sp. nov., isolated from soil

A novel Gram-negative bacterial strain BT320^T was isolated from soil collected in Uijeongbu city, Korea. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain BT320^T belong to a distinct lineage within the genus Flavisolibacter (family Chitinophagaceae, order Chitinophagales, class Chitinophagia). The strain BT320^T was closely related to Flavisolibacter galbus 17J28-26^T (97.6% 16S rRNA gene similarity), Flavisolibacter nicotianae X7X^T (96.7%), Flavisolibacter ginsengiterrae Gsoil 492^T (96.2%), and Flavisolibacter ginsengisoli Gsoil 643 ^T (96.1%). The genome size of strain BT320^T was 5,664,094 bp. Bacterial growth was observed at 10-37 °C (optimum 25 °C) and pH 6.0-8.0 (optimum pH 7.0) on R2A agar. The major cellular fatty acids of strain BT320^T were iso-C_15:0, summed feature 3 (C_16:1 ω6c/C_16:1 ω7c), and summed feature 1 (iso-C_15:1 H/C_13:0 3OH). Its predominant respiratory quinone was MK-7. The major polar lipid of strain BT320^T was identified to be phosphatidylethanolamine (PE). Based on the biochemical, chemotaxonomic, and phylogenetic analysis, strain BT320^T can be suggested as a novel bacterial species within the genus Flavisolibacter and the proposed name is Flavisolibacter longurius. The type strain of Flavisolibacter longurius is BT320^T (= KCTC 72422^T = NBRC 114375^T).