Different types of agricultural land use drive distinct soil bacterial communities.

Biogeographic patterns in soil bacterial communities and their responses to environmental variables are well established, yet little is known about how different types of agricultural land use affect bacterial communities at large spatial scales. We report the variation in bacterial community structures in greenhouse, orchard, paddy, and upland soils collected from 853 sites across the Republic of Korea using 16S rRNA gene pyrosequencing analysis. Bacterial diversities and community structures were significantly differentiated by agricultural land-use types. Paddy soils, which are intentionally flooded for several months during rice cultivation, had the highest bacterial richness and diversity, with low community variation. Soil chemical properties were dependent on agricultural management practices and correlated with variation in bacterial communities in different types of agricultural land use, while the effects of spatial components were little. Firmicutes, Chloroflexi, and Acidobacteria were enriched in greenhouse, paddy, and orchard soils, respectively. Members of these bacterial phyla are indicator taxa that are relatively abundant in specific agricultural land-use types. A relatively large number of taxa were associated with the microbial network of paddy soils with multiple modules, while the microbial network of orchard and upland soils had fewer taxa with close mutual interactions. These results suggest that anthropogenic agricultural management can create soil disturbances that determine bacterial community structures, specific bacterial taxa, and their relationships with soil chemical parameters. These quantitative changes can be used as potential biological indicators for monitoring the impact of agricultural management on the soil environment.

A preliminary examination of bacterial, archaeal, and fungal communities inhabiting different rhizocompartments of tomato plants under real-world environments.

Plant microbiota is a key determinant of plant health and productivity. The composition and structure of plant microbiota varies according to plant tissue and compartment, which are specific habitats for microbial colonization. To investigate the structural composition of the microbiome associated with tomato roots under natural systems, we characterized the bacterial, archaeal, and fungal communities of three belowground compartments (rhizosphere, endosphere, and bulk soil) of tomato plants collected from 23 greenhouses in 7 geographic locations of South Korea. The microbial diversity and structure varied by rhizocompartment, with the most distinctive community features found in the endosphere. The bacterial and fungal communities in the bulk soil and rhizosphere were correlated with soil physicochemical properties, such as pH, electrical conductivity, and exchangeable cation levels, while this trend was not evident in the endosphere samples. A small number of core bacterial operational taxonomic units (OTUs) present in all samples from the rhizosphere and endosphere represented more than 60% of the total relative abundance. Among these core microbes, OTUs belonging to the genera Acidovorax, Enterobacter, Pseudomonas, Rhizobium, Streptomyces, and Variovorax, members of which are known to have beneficial effects on plant growth, were more relatively abundant in the endosphere samples. A co-occurrence network analysis indicated that the microbial community in the rhizosphere had a larger and more complex network than those in the bulk soil and endosphere. The analysis also identified keystone taxa that might play important roles in microbe-microbe interactions in the community. Additionally, profiling of predicted gene functions identified many genes associated with membrane transport in the endospheric and rhizospheric communities. Overall, the data presented here provide preliminary insight into bacterial, archaeal, and fungal phylogeny, functionality, and interactions in the rhizocompartments of tomato roots under real-world environments.

Paenibacillus nuruki sp. nov., isolated from Nuruk, a Korean fermentation starter.

A Gram-stain-positive, rod-shaped, non-endospore-forming motile by means of peritrichous flagella, facultatively anaerobic bacterium designated TI45-13arT was isolated from Nuruk, a Korean traditional Makgeolli fermentation starter. It grew at 4-35°C (optimum, 28-30°C), pH 5.0-9.0 (optimum, pH 7.0) and NaCl concentrations up to 5% (w/v). Phylogenetic trees generated using 16S rRNA gene sequences revealed that strain TI45-13arT belonged to the genus Paenibacillus and showed the highest sequence similarities with Paenibacillus kyungheensis DCY88T (98.5%), Paenibacillus hordei RH-N24T (98.4%) and Paenibacillus nicotianae YIM h-19T (98.1%). The major fatty acid was anteiso-C15:0. The DNA G+C content was 39.0 mol%, and MK-7 was the predominant isoprenoid quinone. The polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, three unidentified glycolipids, and one unidentified aminoglycolipid. The cell-wall peptidoglycan contained meso-diaminopimelic acid. On the basis of polyphasic taxonomy study, it was suggested that strain TI45-13arT represents a novel species within the genus Paenibacillus for which the name Paenibacillus nuruki sp. nov. is proposed. The type strain was TI45-13arT (= KACC 18728T = NBRC 112013T).

Lactobacilus nuruki sp. nov., isolated from Nuruk, a Korean fermentation starter.

A rod-shaped, Gram-stain-positive, non-flagellated, facultatively anaerobic bacterium, designated SYF10-1aT, was isolated from Nuruk, a Korean traditional fermentation starter. It grew at 4-40 °C (optimum 37 °C), at pH 3.0-9.0 (optimum, pH 7.0) and with 0-5 % (w/v) NaCl. Phylogenetic analysis using 16S rRNA gene sequences revealed that strain SYF10-1aT belonged to the genus Lactobacillus and showed the highest sequence similarity of 98.7 % to Lactobacillus crustorum LMG 23699T. A comparison of two housekeeping genes, pheS and rpoA, supported the suggestion that strain SYF10-1aT fell within the radius of the genus Lactobacillus, but was clearly separated from its closest related species. The average nucleotide identity value and digital DNA-DNA hybridization value between strain SYF10-1aT and the most closely related species,L. crustorum LMG 23699T, were 80.5 and 33.3 %, respectively. The predominant cellular fatty acids were C16 : 0, C18 : 1ω9c, C18 : 1ω7c and summed feature 3 (including iso-C15 : 0 2-OH and/or C16 : 1ω7c). Polar lipids were diphosphatidylglycerol, phosphatidylglycerol, two unidentified aminolipids and two unidentified glycolipids. The cell-wall peptidoglycan was of the A4α type with an interpeptide bridge comprising l-Lys-d-Asp. The DNA G+C content was 34.2 mol%. On the basis of this taxonomic study, strain SYF10-1aT represents a novel species within the genus Lactobacillus, for which the name Lactobacillus nuruki sp. nov. is proposed. The type strain is SYF10-1aT (=KACC 18726T=NBRC 112011T).

HR-Mediated Defense Response is Overcome at High Temperatures in Capsicum Species.

Resistance to Tomato spotted wilt virus isolated from paprika (TSWV-Pap) was overcome at high temperatures (30 ± 2°C) in both accessions of Capsicum annuum S3669 (Hana Seed Company) and C. chinense PI15225 (AVRDC Vegetable Genetic Resources). S3669 and PI15225, which carrying the Tsw gene, were mechanically inoculated with TSWV-Pap, and then maintained in growth chambers at temperatures ranging from 15 ± 2°C to 30 ± 2°C (in 5°C increments). Seven days post inoculation (dpi), a hypersensitivity reaction (HR) was induced in inoculated leaves of PI152225 and S3669 plants maintained at 25°C ± 2°C. Meanwhile, necrotic spots were formed in upper leaves of 33% of PI15225 plants maintained at 30 ± 2°C, while systemic mottle symptoms developed in 50% of S3669 plants inoculated. By 15 dpi, 25% of S3669 plants had recovered from systemic mottling induced at 30 ± 2°C. These results demonstrated that resistance to TSWV-Pap can be overcome at higher temperatures in both C. chinense and C. annuum. This is the first study reporting the determination of temperatures at which TSWV resistance is overcome in a C. annuum genetic resource expressing the Tsw gene. Our results indicated that TSWV resistance shown from pepper plants possess the Tsw gene could be overcome at high temperature. Thus, breeders should conduct evaluation of TSWV resistance in pepper cultivars at higher temperature than 30°C (constant temperature).

Temperature and CO2 Level Influence Potato leafroll virus Infection in Solanum tuberosum.

We determined the effects of atmospheric temperature (10-30 ± 2°C in 5°C increments) and carbon dioxide (CO2) levels (400 ± 50 ppm, 540 ± 50 ppm, and 940 ± 50 ppm) on the infection of Solanum tuberosum cv. Chubaek by Potato leafroll virus (PLRV). Below CO2 levels of 400 ± 50 ppm, the PLRV infection rate and RNA content in plant tissues increased as the temperature increased to 20 ± 2°C, but declined at higher temperatures. At high CO2 levels (940 ± 50 ppm), more plants were infected by PLRV at 30 ± 2°C than at 20 or 25 ± 2°C, whereas PLRV RNA content was unchanged in the 20-30 ± 2°C temperature range. The effects of atmospheric CO2 concentration on the acquisition of PLRV by Myzus persicae and accumulation of PLRV RNA in plant tissues were investigated using a growth chamber at 20 ± 2°C. The M. persicae PLRV RNA content slightly increased at elevated CO2 levels (940 ± 50 ppm), but this increase was not statistically significant. Transmission rates of PLRV by Physalis floridana increased as CO2 concentration increased. More PLRV RNA accumulated in potato plants maintained at 540 or 940 ± 50 ppm CO2, than in plants maintained at 400 ± 50 ppm. This is the first evidence of greater PLRV RNA accumulation and larger numbers of S. tuberosum plants infected by PLRV under conditions of combined high CO2 levels (940 ± 50 ppm) and high temperature (30 ± 2°C).

Chitinophaga rhizosphaerae sp. nov., isolated from rhizosphere soil of a tomato plant.

An aerobic, Gram-stain-negative, non-spore-forming, non-flagellated, rod-shaped or filamentous bacterial strain, T16R-86T, was isolated from rhizosphere of a tomato plant collected from a farm on Buyeo-gun, Chungcheongnam-do, South Korea. It grew at the temperature range 10-37 °C (optimum, 28 °C) and pH range 6.0-9.0 (optimum, pH 7.0), and tolerated up to 2 % (w/v) NaCl. According to 16S rRNA gene sequence analysis, strain T16R-86T shared the highest similarity with Chitinophaga barathri YLT18T (96.8 %) and C. pinensis DSM 2588T (96.7 %), forming a subcluster with C. barathri YLT18T, C. cymbidii R156-2T and C. niabensis JS13-10T in the phylogenetic tree. The major fatty acids were iso-C15 : 0, C16 : 1ω5c and iso-C17 : 0 3-OH. The predominant respiratory quinone was menaquinone MK-7. Polar lipids were phosphatidylethanolamine, five unknown aminolipids, an unknown aminophospholipid, one unknown phospholipid and two unknown lipids. The DNA G+C content was 53.6 mol%. The phenotypic, chemotaxonomic and phylogenetic data showed that strain T16R-86T represents a novel species of the genus Chitinophaga, for which the name Chitinophaga rhizosphaerae sp. nov. is proposed. The type strain is T16R-86T (=KACC 18790T=JCM 31600T).

Parapedobacter lycopersici sp. nov., isolated from the rhizosphere soil of tomato plants (Solanum lycopersicum L.).

A novel Gram-stain-negative bacterial strain, designated T16R-256T, was isolated from the rhizosphere soil of tomato plants grown in a greenhouse in Yecheon-gun, Gyeongsangbuk-do, Republic of Korea and characterized using polyphasic taxonomy. Cells were aerobic, non-flagellated and rod-shaped. Colonies were light yellow, convex and round. The strain grew in the temperature range of 15-37 °C (optimally at 28-30 °C) and pH range of 7.0-9.0 (optimally at 7.0-8.0) and in 4 % NaCl (w/v). A comparison of 16S rRNA gene sequences showed that strain T16R-256T is a member of the genus Parapedobacter, exhibiting high sequence similarity with Parapedobacter pyrenivorans P-4T (94.2 %), Parapedobacter indicus RK1T (93.7 %), Parapedobacter koreensis Jip14T (93.7 %), Parapedobacter luteus 4M29T (93.6 %) and Parapedobacter soli DCY14T (93.4 %). The major polar lipids were phosphatidylethanolamine, sphingolipid, one aminophospholipid, two aminolipids and three unknown lipids. The major fatty acids (>10 % of the total fatty acids) were iso-C15 : 0, iso-C17 : 0 3-OH and iso-C15 : 0 2-OH/C16 : 1ω7c. Strain T16R-256T contained MK-7 as the predominant respiratory quinone and homospermidine as the major polyamine. The genomic DNA G+C content of the type strain was 55.5 mol%. On the basis of phenotypic, chemotaxonomic and phylogenetic data, strain T16R-256T should be designated as representative of a novel species of the genus Parapedobacter, for which the name Parapedobacter lycopersici sp. nov. is proposed. The type strain is T16R-256T (=KACC 18788T=JCM 31602T).

Terrimonas terrae sp. nov., isolated from the rhizosphere of a tomato plant.

A yellow, aerobic, Gram-stain-negative, non-motile, rod-shaped and non-flagellated bacterial strain, designated T16R-129T, was isolated from the rhizosphere of a tomato plant collected at a farm located on Buyeo-gun of Chungcheongnam-do, South Korea. Strain T16R-129T grew at 15-40 °C and pH 7.0-9.0, and did not require NaCl for growth. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain T16R-129T clustered with members of the genus Terrimonas, and it shared highest similarity with Terrimonas arctica R9-86T (96.1 %), Terrimonas pekingensis QHT (95.9 %), Terrimonas lutea DYT (94.9 %), Terrimonas crocea M1-33108T (95.4 %) and Terrimonas rhizosphaerae CR94T (95.3 %). The major isoprenoid quinone was menaquinone 7 (MK-7). The major cellular fatty acids were iso-C15 : 0, iso-C17 : 0 3-OH and iso-C15 : 1 G. The polar lipids of strain T16R-129T were phosphatidylethanolamine, two unidentified aminolipids, two unidentified aminophospholipids and five unidentified polar lipids. The G+C content of the genomic DNA was 46.0 mol%. On the basis of data from this polyphasic taxonomic study, strain T16R-129T represents a novel species in the genus Terrimonas, for which the name Terrimonas terrae sp. nov. is proposed; the type strain is T16R-129T (=KACC 18787T=JCM 31603T).

Nakamurella intestinalis sp. nov., isolated from the faeces of Pseudorhynchus japonicus.

One strain, designated 63MJ-1T, was isolated from fresh faeces of broad-winged katydids collected in Jinan-gun, Jeollabuk-do, the Republic of Korea. The organism stained Gram-positive and was an aerobic, non-flagellated and short-rod-shaped bacterium. The organism grew in the range of 4-35 °C (optimum, 28-30 °C) and pH 6.0-9.0 (optimum, pH 7.0), and in the presence of 5 % NaCl (w/v), but not in media containing 7 % NaCl. According to the 16S rRNA gene sequence analysis, strain 63MJ-1T showed the highest sequence similarities with Nakamurella panacisegetis P4-7T (95.9 %), Nakamurella endophytica 2Q3S-4-2T (95.8 %) and Nakamurella multipartita DSM 44233T (95.7 %). Phylogenetic trees also indicated that strain 63MJ-1T formed one robust cluster with members of the genusNakamurella. The predominant quinone of strain 63MJ-1T was MK-8(H4). Polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, an unidentified aminophospholipid and two unidentified lipids. The major fatty acids were C16 : 0, anteiso-C15 : 0 and iso-C15 : 0. The peptidoglycan type was A1γ with meso-diaminopimelic acid as the diagnostic amino acid. The DNA G+C content was 64.6 mol%. Based on the phylogenetic, physiological and chemotaxonomic data, it was demonstrated that strain 63MJ-1T represents a novel species of the genus Nakamurella, for which the name Nakamurella intestinalis sp. nov. is proposed. The type strain is 63MJ-1T (=KACC 18662T=NBRC 111844T).

Parafilimonas rhizosphaerae sp. nov., isolated from the rhizosphere of tomato plant (Solanum lycopersicum L.).

A bacterial strain, designated T16E-198T, was isolated from the rhizosphere of tomato plant collected from a farm on Buyeo-gun, Chungcheongnam-do, South Korea. The strain was aerobic, Gram-stain-negative, rod-shaped, non-flagellated and yellow-pigmented. Strain T16E-198T was mesophilic, catalase- and oxidase-positive and with flexirubin-type pigments. A phylogenetic tree based on 16S rRNA gene sequences showed that strain T16E-198T formed a lineage with Parafilimonas terrae 5GHs7-2T, sharing highest sequence similarity of 98.4 % with it and less than 93 % with all the other validly published species. The major fatty acids were iso-C15 : 0, iso-C17 : 0 3-OH and iso-C15 : 1 G. The predominant menaquinone was MK-7. The polar lipids were phosphatidylethanolamine, one unknown aminophospholipid, five unknown aminolipids and five unknown lipids. The DNA G+C content was 41.2 mol%. On the basis of the phenotypic, phylogenetic and chemotaxonomic data presented, strain T16E-198T is considered to represent a novel species of the genus Parafilimonas, for which the name Parafilimonas rhizosphaerae sp. nov. is proposed; the type strain is T16E-198T (=KACC 18786T=JCM 31601T).

Erratum: The Effects of High Temperature on Infection by Potato virus Y, Potato virus A, and Potato leafroll virus.

[This corrects the article on p. 321 in vol. 32, PMID: 27493607.].

Lysobacter solanacearum sp. nov., isolated from rhizosphere of tomato.

A bacterial strain, designated T20R-70T, was isolated from tomato rhizosphere soil collected in Yecheon-gun, Gyeongsangbuk-do in South Korea. Growth was observed within the ranges 10-40 °C (optimally at 28-30 °C), pH 7.0-8.0 (optimally at pH 7.0) and 0-1 % NaCl (optimally at 0 %). The 16S rRNA gene sequence showed the highest similarities with those of Lysobacter hankyongensis KTCe-2T (98.7 %), Lysobacter brunescens KCTC 12130T (98.0 %), 'Lysobacter daecheongensis' Dae08 (97.2 %) and Lysobacter oligotrophicus 107-E2T (97.1 %). The phylogenetic tree showed that strain T20R-70T formed a clade with Lysobacterhankyongensis KTCe-2T and Lysobacterbrunescens KCTC 12130T. The dominant fatty acids (>10 %) were iso-C15 : 0, iso-C16 : 0, iso-C17 : 1ω9c and summed feature 3 (including iso-C15 : 0 2-OH and/or iso-C16 : 1ω7c). The major polar lipids were phosphatidylethanolamine, diphosphatidylglycerol and phosphatidylglycerol. The major respiratory quinone was Q-8. DNA-DNA hybridization data revealed that strain T20R-70T had a hybridization value of 42±4 % (mean±sd) to the most closely related species of the genus Lysobacter. The DNA G+C content was 63.0 mol%. The physiological, biochemical and chemotaxonomic data allowed the discrimination of the new isolate from its phylogenetic relatives. Strain T20R-70T is thus considered to be a representative of a novel species of the genus Lysobacter, for which the name Lysobactersolanacearum sp. nov. is proposed. The type strain is T20R-70T (=KACC 18656T=NBRC 111881T).

Pseudactinotalea terrae gen. nov., sp. nov., isolated from greenhouse soil, and reclassification of Actinotalea suaedae as Pseudactinotalea suaedae comb. nov.

A bacterial strain, designated 5GHs33-3T, was isolated from greenhouse soil collected from Yongin region, Gyeonggi province, South Korea. The strain was an aerobic, Gram-stain-positive, flagellated, rod-shaped bacterium. Strain 5GHs33-3T grew at 4-37 °C (optimally at 28-30 °C), pH 6.0-10.0 (optimally at pH 7.0) and with 0-7 % (w/v) NaCl (optimally with 0 %). The 16S rRNA gene sequence analysis revealed that strain 5GHs33-3T had high sequence similarity with Actinotalea suaedae EGI 60002T (98.4 %), Actinotalea ferrariae CF5-4T (96.4 %) and Actinotalea fermentans DSM 3133T (96.2 %), and less than 95.5 % sequence similarity against all the other species with validly published names. The phylogenetic tree revealed that strain 5GHs33-3T formed a robust independent monophyletic line with Actinotalea suaedae EGI 60002T. The predominant fatty acids of strain 5GHs33-3T were anteiso-C15 : 0 and iso-C14 : 0. The only quinone was MK-8(H4). Polar lipids were diphosphatidylglycerol, phosphatidylinositol, an unknown phosphoglycolipid and unknown lipids. The peptidoglycan type was A4ß, with ornithine as the diagnostic diamino acid and an interpeptide bridge comprising l-Glu. The DNA G+C content is 69.0 mol%. Based on phylogenetic evidence and the results of phenotypic, genotypic and chemotaxonomic analyses, strain 5GHs33-3T represents a novel species of a new genus of the family Cellulomonadaceae, for which the name Pseudactinotalea terrae gen. nov., sp. nov. is proposed. The type strain of the type species is 5GHs33-3T (=KACC 16542T=NBRC 111006T). We also propose the reclassification of Actinotalea suaedae as Pseudactinotalea suaedae comb. nov. (type strain EGI 60002T=JCM 19624T=KACC 17839T=KCTC 29256T).

D-PSA-K: A Model for Estimating the Accumulated Potential Damage on Kiwifruit Canes Caused by Bacterial Canker during the Growing and Overwintering Seasons.

We developed a model, termed D-PSA-K, to estimate the accumulated potential damage on kiwifruit canes caused by bacterial canker during the growing and overwintering seasons. The model consisted of three parts including estimation of the amount of necrotic lesion in a non-frozen environment, the rate of necrosis increase in a freezing environment during the overwintering season, and the amount of necrotic lesion on kiwifruit canes caused by bacterial canker during the overwintering and growing seasons. We evaluated the model's accuracy by comparing the observed maximum disease incidence on kiwifruit canes against the damage estimated using weather and disease data collected at Wando during 1994-1997 and at Seogwipo during 2014-2015. For the Hayward cultivar, D-PSA-K estimated the accumulated damage as approximately nine times the observed maximum disease incidence. For the Hort16A cultivar, the accumulated damage estimated by D-PSA-K was high when the observed disease incidence was high. D-PSA-K could assist kiwifruit growers in selecting optimal sites for kiwifruit cultivation and establishing improved production plans by predicting the loss in kiwifruit production due to bacterial canker, using past weather or future climate change data.

Pedobacterlycopersici sp. nov., isolated from the rhizosphere of tomato plant (Solanum lycopersicum L.).

A Gram-stain-negative, rod-shaped, white bacterium, designated strain T16R-88T, was isolated from a rhizosphere soil sample collected in Buyeo-gun of Chungcheongnam-do, South Korea. A phylogenetic tree based on 16S rRNA gene sequences showed that strain T16R-88T formed a lineage within the genus Pedobacter. It showed highest sequence similarities to Pedobacter ginsengisoli Gsoil 104T (97.4 %), Pedobacter nutrimenti J22T (97.2 %), Pedobacter nyackensis NWG-II14T (97.1 %), Pedobacter seoulensis THG-G12T (97.1 %) and Pedobacter panaciterrae Gsoil 042T (97.0 %). The predominant respiratory quinone was menaquinone MK-7. The major cellular fatty acids (>10 % of the total fatty acids) were summed feature 3 (iso-C15 : 0 2-OH and/or C16 : 1ω7c), iso-C17 : 0 3-OH and iso-C15 : 0. The polar lipids consisted of phosphatidylethanolamine, sphingolipid, one unidentified aminophospholipid, three unidentified aminolipids, three unidentified lipids and one unidentified phospholipid. DNA-DNA hybridization values between strain T16R-88T and its most closely related species were below 70 %. The DNA G+C content was 35.6 mol%. On the basis of the evidence presented in this study, strain T16R-88T represents a novel species of the genus Pedobacter, for which the name Pedobacter lycopersici sp. nov. is proposed. The type strain is T16R-88T (=KACC 18652T=NBRC 111984T).

Soil pH and electrical conductivity are key edaphic factors shaping bacterial communities of greenhouse soils in Korea.

Soil microorganisms play an essential role in soil ecosystem processes such as organic matter decomposition, nutrient cycling, and plant nutrient availability. The land use for greenhouse cultivation has been increasing continuously, which involves an intensive input of agricultural materials to enhance productivity; however, relatively little is known about bacterial communities in greenhouse soils. To assess the effects of environmental factors on the soil bacterial diversity and community composition, a total of 187 greenhouse soil samples collected across Korea were subjected to bacterial 16S rRNA gene pyrosequencing analysis. A total of 11,865 operational taxonomic units at a 97% similarity cutoff level were detected from 847,560 sequences. Among nine soil factors evaluated; pH, electrical conductivity (EC), exchangeable cations (Ca2+, Mg2+, Na+, and K+), available P2O5, organic matter, and NO3-N, soil pH was most strongly correlated with bacterial richness (polynomial regression, pH: R2 = 0.1683, P < 0.001) and diversity (pH: R2 = 0.1765, P < 0.001). Community dissimilarities (Bray-Curtis distance) were positively correlated with Euclidean distance for pH and EC (Mantel test, pH: r = 0.2672, P < 0.001; EC: r = 0.1473, P < 0.001). Among dominant phyla (> 1%), the relative abundances of Proteobacteria, Gemmatimonadetes, Acidobacteria, Bacteroidetes, Chloroflexi, and Planctomycetes were also more strongly correlated with pH and EC values, compared with other soil cation contents, such as Ca2+, Mg2+, Na+, and K+. Our results suggest that, despite the heterogeneity of various environmental variables, the bacterial communities of the intensively cultivated greenhouse soils were particularly influenced by soil pH and EC. These findings therefore shed light on the soil microbial ecology of greenhouse cultivation, which should be helpful for devising effective management strategies to enhance soil microbial diversity and improving crop productivity.

Comparative analysis of bacterial diversity in the rhizosphere of tomato by culture-dependent and -independent approaches.

The microbiome in the rhizosphere-the region surrounding plant roots-plays a key role in plant growth and health, enhancing nutrient availability and protecting plants from biotic and abiotic stresses. To assess bacterial diversity in the tomato rhizosphere, we performed two contrasting approaches: culture-dependent and -independent. In the culture-dependent approach, two culture media (Reasoner's 2A agar and soil extract agar) were supplemented with 12 antibiotics for isolating diverse bacteria from the tomato rhizosphere by inhibiting predominant bacteria. A total of 689 bacterial isolates were clustered into 164 operational taxonomic units (OTUs) at 97% sequence similarity, and these were found to belong to five bacterial phyla (Proteobacteria, Actinobacteria, Bacteroidetes, Acidobacteria, and Firmicutes). Of these, 122 OTUs were retrieved from the antibiotic-containing media, and 80 OTUs were recovered by one specific antibiotic-containing medium. In the culture-independent approach, we conducted Illumina MiSeq amplicon sequencing of the 16S rRNA gene and obtained 19,215 high-quality sequences, which clustered into 478 OTUs belonging to 16 phyla. Among the total OTUs from the MiSeq dataset, 22% were recovered in the culture collection, whereas 41% of OTUs in the culture collection were not captured by MiSeq sequencing. These results showed that antibiotics were effective in isolating various taxa that were not readily isolated on antibiotic-free media, and that both contrasting approaches provided complementary information to characterize bacterial diversity in the tomato rhizosphere.

Siphonobacter intestinalis sp. nov., a bacterium isolated from the feces of Pseudorhynchus japonicus.

Strain 63MJ-2T was isolated from the feces of broad-winged katydid (Pseudorhynchus japonicus) collected in Korea. The 16S rRNA gene sequence of this strain showed the highest sequence similarity with that of Siphonobacter aquaeclarae P2T (96.1%) and had low similarities (below 86.3%) with those of other members of family 'Flexibacteraceae'. The strain 63MJ-2T is a strictly aerobic, Gram-stain-negative, non-motile, rod-shaped bacterium. The strain grew at 4-35°C (optimum, 25-30°C), pH of 5.0-9.0 (optimum, 6.0-7.0), and 0-2.0% (optimum, 1.0-2.0) (w/v) NaCl. The DNA G+C content of strain 63MJ-2T was 43.5 mol%. The major fatty acids were C16:1 ω5c (42.5%), iso-C17:0 3-OH (18.7%), and summed feature 3 (iso-C15:0 2-OH and/or C16:1 ω7c, 18.0%). The major menaquinone was MK-7 and polar lipids were phosphatidylethanolamine, six unknown aminolipids, and five unknown lipids. Based on the evidence from our polyphasic taxonomic study, we conclude that strain 63MJ-2T should be classified as a novel species of the genus Siphonobacter, and propose the name Siphonobacter intestinalis sp. nov. The type strain is 63MJ-2T (=KACC 18663T =NBRC 111883T).

The Effects of High Temperature on Infection by Potato virus Y, Potato virus A, and Potato leafroll virus.

We examined the effects of temperature on acquisition of Potato virus Y-O (PVY-O), Potato virus A (PVA), and Potato leafroll virus (PLRV) by Myzus persicae by performing transmission tests with aphids that acquired each virus at different temperatures. Infection by PVY-O/PVA and PLRV increased with increasing plant temperature in Nicotiana benthamiana and Physalis floridana, respectively, after being transmitted by aphids that acquired them within a temperature range of 10-20°C. However, infection rates subsequently decreased. Direct qRT-PCR of RNA extracted from a single aphid showed that PLRV infection increased in the 10-20°C range, but this trend also declined shortly thereafter. We examined the effect of temperature on establishment of virus infection. The greatest number of plants became infected when N. benthamiana was held at 20°C after inoculation with PVY-O or PVA. The largest number of P. floridana plants became infected with PLRV when the plants were maintained at 25°C. PLRV levels were highest in P. floridana kept at 20-25°C. These results indicate that the optimum temperatures for proliferation of PVY-O/PVA and PLRV differed. Western blot analysis showed that accumulations of PVY-O and PVA coat proteins (CPs) were lower at 10°C or 15°C than at 20°C during early infection. However, accumulation increased over time. At 25°C or 30°C, the CPs of both viruses accumulated during early infection but disappeared as time passed. Our results suggest that symptom attenuation and reduction of PVY-O and PVA CP accumulation at higher temperatures appear to be attributable to increased RNA silencing.