Effect of long-term different fertilization on bacterial community structures and diversity in citrus orchard soil of volcanic ash

This study was conducted to assess bacterial species richness, diversity and community distribution according to different fertilization regimes for 16 years in citrus orchard soil of volcanic ash. Soil samples were collected and analyzed from Compost (cattle manure, 2,000 kg/10a), 1/2 NPK+compost (14-20-14+2,000 kg/10a), NPK+compost (28-40-28+2,000 kg/10a), NPK (28-40-28 kg/10a), 3 NPK (84-120-84 kg/10a), and Control (no fertilization) plot which have been managed in the same manners with compost and different amount of chemical fertilization. The range of pyrosequencing reads and OTUs were 4,687–7,330 and 1,790–3,695, respectively. Species richness estimates such as Ace, Chao1, and Shannon index were higher in 1/2 NPK+compost than other treatments, which were 15,202, 9,112, 7.7, respectively. Dominant bacterial groups at level of phylum were Proteobacteria, Acidobacteria, and Actinobacteria. Those were occupied at 70.9% in 1/2 NPK+compost. Dominant bacterial groups at level of genus were Pseudolabrys, Bradyrhizobium, and Acidobacteria. Those were distributed at 14.4% of a total of bacteria in Compost. Soil pH displayed significantly closely related to bacterial species richness estimates such as Ace, Chao1 (p<0.05) and Shannon index (p<0.01). However, it showed the negative correlation with exchangeable aluminum contents (p<0.05). In conclusion, diversity of bacterial community in citrus orchard soil was affected by fertilization management, soil pH changes and characteristics of volcanic ash.     

Decrease in heathland soil labile organic carbon under future atmospheric and climatic conditions

Characterization of the impacts of climate change on terrestrial carbon (C) cycling is important due to possible feedback mechanisms to atmospheric CO₂ concentrations. We investigated soil organic matter (SOM) dynamics in the A1 and A2 horizons (~0–5.1 and ~5.1–12.3 cm depth, respectively) of a shrubland grass (Deschampsia flexuosa) after 8 years of exposure to: elevated CO₂ (CO₂), summer drought (D), warming (T) and all combinations hereof, with TDCO₂ simulating environmental conditions for Denmark in 2075. The mean C residence time was highest in the heavy fraction (HF), followed by the occluded light fraction and the free light fraction (fLF), and it increased with soil depth, suggesting that C was stabilized on minerals at depth. A2 horizon SOM was susceptible to climate change whereas A1 horizon SOM was largely unaffected. The A2 horizon fLF and HF organic C stocks decreased by 43 and 23% in response to warming, respectively. Organic nitrogen (N) stocks of the A2 horizon fLF and HF decreased by 50 and 17%, respectively. Drought decreased the A2 horizon fLF N stock by 38%. Elevated CO₂ decreased the A2 horizon fLF C stock by 39% and the fLF N stock by 50%. Under TDCO₂, A2 horizon fLF C and N stocks decreased by 22 and 40%, respectively. Overall, our results indicate that shrubland SOM will be susceptible to increased turnover and associated net C and N losses in the future.     

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.     

Plant species-specificity and effects of bioinoculants and fertilization on plant performance for nickel phytomining

Aims

To investigate the effects of fertilization and bacterial inoculation on the growth, health and Ni phytoextraction capacity of three Ni-hyperaccumulators, Odontarrhena bracteata, O. inflata and O. serpyllifolia.

Methods

Plants were grown for three months in serpentine soil fertilized with inorganic NPK or amended with cow manure and inoculated with five rhizobacterial strains (previously isolated from O. serpyllifolia). Shoot and root dry weight (DW) yields, Ni accumulation and removal, nutritive status and stress indicators were determined.

Results

Plants grown in manure-amended soil showed significantly higher DW yields, improved nutritive status and higher total Ni phytoextracted. Some bacterial inoculants enhanced Ni removal due to the stimulation in growth and/or increase in shoot Ni concentration but this depended on the plant species, soil type and inoculant. Pseudoarthrobacter oxydans strain SBA82 enhanced shoot DW yield of all three Odontarrhena spp. in at least one soil type. Paenarthrobacter sp. strain LA44 and Stenotrophomonas sp. strain MA98 promoted growth of O. serpyllifolia and O. bracteata. Inoculated plants showing growth promotion presented lower activities of antioxidative enzymes, and concentrations of malondialdehyde (MDA) and H₂O₂, indicating a protective effect of these inoculants on the plants.

Conclusion

Rhizobacterial inoculants applied in combination with manure can improve plant growth and health, and Ni phytoextraction, in some hyperaccumulating Odontarrhena spp.

     

Vertical profiles of microbial communities in perfluoroalkyl substance-contaminated soils

Poly- and perfluoroalkyl compounds (PFASs) are ubiquitous in the environment, but their influences on microbial community remain poorly known. The present study investigated the depth-related changes of archaeal and bacterial communities in PFAS-contaminated soils. The abundance and structure of microbial community were characterized using quantitative PCR and high-throughput sequencing, respectively. Microbial abundance changed considerably with soil depth. The richness and diversity of both bacterial and archaeal communities increased with soil depth. At each depth, bacterial community was more abundant and had higher richness and diversity than archaeal community. The structure of either bacterial or archaeal community displayed distinct vertical variations. Moreover, a higher content of perfluorooctane sulfonate (PFOS) could have a negative impact on bacterial richness and diversity. The rise of soil organic carbon content could increase bacterial abundance but lower the richness and diversity of both bacterial and archaeal communities. In addition, Proteobacteria, Actinobacteria, Chloroflexi, Cyanobacteria, and Acidobacteria were the major bacterial groups, while Thaumarchaeota, Euryarchaeota, and unclassified Archaea dominated in soil archaeal communities. PFASs could influence soil microbial community.     

Biodiversity of arbuscular mycorrhizal fungi in the drawdown zone of the Three Gorges Reservoir under different fertilization histories

Impoundment of the Three Gorges Reservoir (TGR) has dramatically influenced the riparian environment and shaped a new drawdown zone, which has experienced long-term winter conditions and short periods of summer flooding. The community structure and diversity of arbuscular mycorrhizal (AM) fungi (AMF) were investigated in three areas with different fertilization histories [Area A (5 years of fertilization), Area B (3 years of fertilization) and Area C (no fertilization)] in the drawdown zone of the TGR. Altogether, 50 AMF species were identified; the genera Acaulospora, Funneliformis and Glomus were predominant. The AM fungal community differed among areas A, B and C. A higher isolation frequency and relative abundance of Acaulospora, Ambispora, Entrophospora and Paraglomus were observed in areas A and B; however, Claroideoglomus, Diversispora, Sclerocystis and Septoglomus were more abundant in Area C. The highest spore density occurred in Area C, and was slightly lower in Area A and lowest in Area B. Conversely, species richness and diversity indices (Shannon–Wiener and evenness indices) were the highest in Area A, followed by areas C and B. Based on nonmetric multidimensional scaling analyses, the distribution of AMF was influenced by plant host, fertilization practice and environmental factors. Among them, the soil physicochemical properties were the main drivers affecting AMF, in which three edaphic attributes (carbon/nitrogen ratio, available phosphorus and potassium content) were significantly correlated (P < 0.001) with the AM fungal community composition in the three areas of the drawdown zone of the TGR.     

Characterization of phosphate-solubilizing bacteria exhibiting the potential for growth promotion and phosphorus nutrition improvement in maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.) in calcareous soils of Sinaloa,Mexico

Greenhouse bioassays were used to examine the ability of selected strains of the rhizobacteria Sinorhizobium meliloti, Bacillus flexus and B. megaterium to solubilize phosphorus (P) and to affect growth promotion and phosphorus nutrition in maize. These bacterial strains were found to decrease the pH and solubilize some forms of insoluble P, such as tricalcium phosphate and hydroxyapatite, as well as to exhibit acid and alkaline phosphatase enzymatic activities in culture medium, properties that are possibly involved in P solubilization. Inoculation of the strains separately and as a consortium of the three bacteria (S. meliloti, B. flexus and B. megaterium) in P-deficient soil (4.33 w/v P) fertilized without P improved plant height, shoot and root dry weight, as well as P nutrition in the maize plants. Use of the B. flexus and B. megaterium strains separately and in a consortium positively affected several growth parameters and P nutrition in plants supplemented with insoluble P. No effect was observed when pots in which the seedlings were growing were supplied with soluble fertilizer. A second assay using a P-deficient soil (6.64 w/v P) showed that inoculation with the consortium of B. flexus and B. megaterium significantly increased growth and total P content in maize plants. A dose–response P fertilization experiment using sterile P-deficient soil led us to conclude that inoculation to soil of the mixture of B. flexus and B. megaterium may improve P nutrition and growth to a level previously attained by the addition of soluble P-fertilizer at 40 w/v P. A non-sterile experiment showed a beneficial response with B. megaterium but not with B. flexus. We propose utilizing these bacteria in P-deficient alkaline soils in future field trials in order to evaluate their potential as biofertilizers.     

Dynamics of bacterial communities in rice field soils as affected by different long-term fertilization practices

Fertilization and the response of the soil microbial community to the process significantly affect crop yield and the environment. In this study, the seasonal variation in the bacterial communities in rice field soil subjected to different fertilization treatments for more than 50 years was investigated using 16S rRNA sequencing. The simultaneous application of inorganic fertilizers and rice straw compost (CAPK) maintained the species richness of the bacterial communities at levels higher than that in the case of non-fertilization (NF) and application of inorganic fertilizers only (APK) in the initial period of rice growth. The seasonal variation in the bacterial community structure in the NF and APK plots showed cyclic behavior, suggesting that the effect of season was important; however, no such trend was observed in the CAPK plot. In the CAPK plot, the relative abundances of putative copiotrophs such as Bacteroidetes, Firmicutes, and Proteobacteria were higher and those of putative oligotrophs such as Acidobacteria and Plactomycetes were lower than those in the other plots. The relative abundances of organotrophs with respiratory metabolism, such as Actinobacteria, were lower and those of chemoautotrophs that oxidize reduced iron and sulfur compounds were higher in the CAPK plot, suggesting greater carbon storage in this plot. Increased methane emission and nitrogen deficiency, which were inferred from the higher abundances of Methylocystis and Bradyrhizobium in the CAPK plot, may be a negative effect of rice straw application; thus, a solution for these should be considered to increase the use of renewable resources in agricultural lands.     

Root-exudate flux variations among four co-existing canopy species in a temperate forest,Japan

Plants allocate carbon to root exudates to mine nitrogen (N) from soil organic matter (SOM). Little is known about how the root-exudation rate varies among co-existing woody species. We conducted an in situ experiment in a warm temperate forest on two dominant species, Quercus serrata and Ilex pedunculosa, and two of their congeneric species, Quercus glauca and Ilex macropoda, respectively. We hypothesized that the root-exudation rate varies among these species because of their distinct functional traits and N demands. Root-exudation rates were measured using a non-soil culture method during the growing season from June 2013 to May 2014. We also measured foliar N concentrations and the activities of N-degrading enzymes in the rhizosphere soils. The annual demand for N was calculated from the growth rate and allometric equations for biomass. The root-exudation rates of Q. serrata and I. macropoda were consistently greater than those of their congeneric evergreen species on root-length, root-weight, and individual-tree bases. The variations of the annual N demand of these species mirrored this pattern. Within a species, root-exudation rates correlated positively to leaf N contents, suggesting a physiological linkage between photosynthetic capacities and belowground carbon allocation. Root-exudation rates also correlated positively to the activities of polyphenol oxidase, an enzyme that decomposes N from recalcitrant SOM. Our results suggest that the variations of the root-exudation among co-existing species relate to their functional traits and demand for N.     

Recombinant protein,AlnA, combined with transgenic alfalfa remediates polychlorinated biphenyl-contaminated soils: efficiency and rhizosphere microbial community response

Objective

To investigate the remediation efficiency of polychlorinated biphenyl (PCB)-contaminated soils by the combination of a bioemulsifying protein, AlnA, and alfalfa expressing bphC.

Result

The combination of AlnA and transgenic alfalfa promoted PCB soil remediation through the pot experiments. The removal rates of tri-PCBs (PCB 16/PCB 32 and PCB 31/PCB 28) and tetra-PCB (PCB 49) in transgenic alfalfa/AlnA treatment were 3.6-, 1.1-, and 2-fold higher than in transgenic alfalfa treatment alone. Analysis of gene copy number revealed that the PCB-degrading gene, bphC, of Pseudomonas-like bacterial populations in transgenic alfalfa/AlnA treatment increased 1.5-fold compared with that of unplanted soils. Bacterial community Illumina sequencing showed Pseudomonas, Arthrobacter, and Sphingomonas positively correlated with the removal rates of PCBs.

Conclusions

PCB removal was unrelated to bacterial community diversity but positively correlated with their specific degraders and bphC gene expression.

     

Production of thermotolerant entomopathogenic fungal conidia on millet grain

Thermotolerance of entomopathogenic (insect-killing) fungi should be seriously considered before industrialization. This work describes the feasibility of millet grain as a substrate for production of thermotolerant Beauveria bassiana (Bb) GHA and ERL1170 and Metarhizium anisopliae (Ma) ERL1171 and ERL1540 conidia. First, conidial suspensions of the Bb isolates, produced on millet grain in polyethylene bags, were exposed to five temperatures (43–47°C) at 15-min intervals for up to 120 min (experiment I). Agar-based quarter-strength (¼) Sabouraud dextrose agar supplemented with yeast extract (SDAY) and whey permeate media served as controls. Millet-grain-based culture was superior in producing the most thermotolerant Bb conidia, followed by whey permeate agar and ¼SDAY-based cultures. Secondly, to compare the thermotolerance of conidia produced at the same conditions, the Bb isolates were then produced on agar-based millet powder medium, with ¼SDAY and whey permeate agar media as controls, and the two Ma isolates were added (experiment II). They were then exposed to the same temperatures as above. More thermotolerant Bb and Ma conidia were produced on millet powder agar than on whey permeate agar and ¼SDAY overall. These results suggest that millet grain can be used as a substrate to produce thermotolerant conidia in a mass production system.     

Foxtail Millet CBL4 (SiCBL4) Interacts with SiCIPK24, Modulates Plant Salt Stress Tolerance

The calcineurin B-like (CBL) protein and the CBL-interacting protein kinase (CIPK) signaling pathway play important roles in plant abiotic stress tolerance. To investigate the molecular mechanism of salt stress tolerance of foxtail millet, SiCBL4 and SiCIPK24 were identified and functionally characterized. Both SiCBL4 and SiCIPK24 were induced by salt, abscisic acid (ABA), methyl viologen (MV), and heat shock stress in foxtail millet seedlings. Yeast two-hybrid and bimolecular fluorescence complementation assay showed that SiCBL4 interacted with SiCIPK24. The mutation of the N-myristoylation site of SiCBL4 changed the sub-cellular localization of SiCBL4 and directed the SiCBL4-SiCIPK24 protein complex from plasma membrane to cytoplasm, and disrupted its function in plant salt stress tolerance. Overexpression of SiCBL4 or SiCIPK24 in Arabidopsis sos3-1 or sos2-1 mutant plants rescued the mutant salt hypersensitivity phenotype. In addition, overexpression of SiCIPK24 also enhanced the salt stress tolerance of Arabidopsis wild-type plants. This work helps to understand the structure and function of the foxtail millet CBL and CIPK genes and confirmed that the foxtail millet CBL-CIPK pathway can be manipulated to enhance the plant salt stress tolerance.     

Impact of high temperature on sucrose translocation,sugar content and inulin yield in <Emphasis Type="Italic">Cichorium intybus</Emphasis> L. var. <Emphasis Type="Italic">sativum</Emphasis>

Aims

Dianthus caryophyllus is a commercially important ornamental flower. Plant growth promoting rhizobacteria are increasingly applied as bio-fertilisers and bio-fortifiers. We studied the effect of a rhizospheric isolate Klebsiella SGM 81 strain to promote D. caryophyllus growth under sterile and non-sterile conditions, to colonise its root system endophytically and its impact on the cultivatable microbial community. We identified the auxin indole-3-acetic acid (IAA) production of Klebsiella SGM 81 as major bacterial trait most likely to enhance growth of D. caryophyllus.

Methods

ipdC dependent IAA production of SGM 81 was quantified using LC-MS/MS and localised proximal to D. caryophyllus roots and correlated to root growth promotion and characteristic morphological changes. SGM 81 cells were localised on and within the plant root using 3D rendering confocal microscopy of gfp expressing SGM 81. Using Salkowski reagent IAA production was quantified and localised proximal to roots in situ. The effect of different bacterial titres on rhizosphere bacterial population was CFU enumerated on nutrient agar. The genome sequence of Klebsiella SGM 81 (accession number PRJEB21197) was determined to validate PGP traits and phylogenic relationships.

Results

Inoculation of D. caryophyllus roots with Klebsiella SGM 81 drastically promoted plant growth when grown in agar and soil, concomitant with a burst in root hair formation, suggesting an increase in root auxin activity. We sequenced the Klebsiella SGM 81 genome, identified the presence of a canonical ipdC gene in Klebsiella SGM 81, confirmed bacterial production and secretion of IAA in batch culture using LC-MS/MS and localised plant dependent IAA production by SGM 81 proximal to roots. We found Klebsiella SGM 81 to be a rhizoplane and endophytic coloniser of D. caryophyllus roots in a dose dependent manner. We found no adverse effects of SGM 81 on the overall rhizospheric microbial population unless supplied to soil in very high titres.

Conclusion

Klebsiella SGM 81 effectively improves root traits of D. caryophyllus in a dose dependent manner, likely through tryptophan dependent IAA production in the rhizoplane and potentially within the intercellular spaces of root tissue. Under optimal plant growth promoting conditions in non-sterile soil, the high total microbial titre in the rhizosphere supports a mutualistic relationship between Klebsiella SGM 81 and carnation that potentially extends to the wider rhizosphere microbiota.

     

Water and nitrogen supply effects on four desert shrubs with potential use for rehabilitation activities

Desert evergreen shrubs, which are adapted to low-fertility ecosystems, generally exhibit limited responses to increased nutrient availability and tend to absorb and store nutrients rather than synthesize new tissues. The objective of this work was to analyze the effect of nitrogen fertilization combined with soil water availability on growth, nitrogen content, and nitrogen use efficiency on four shrubs (Atriplex lampa, Capparis atamisquea, Larrea cuneifolia, and Senecio subulatus) from the Monte Desert. In a 120-day glasshouse experiment in Mendoza, Argentina, we compared the effects of three levels of nitrogen fertilization combined with two levels of water availability on seedling biomass, nitrogen content, water potential, and nitrogen use efficiency. Fertilization induced a higher biomass on A. lampa under high water availability and on C. atamisquea regardless of water level. Shoot:root ratios of these two species were lower under water stress without fertilization. On the other hand, L. cuneifolia presented lower root biomass and lower water potential with N fertilization. All species when fertilized exhibited higher nitrogen content and lower nitrogen use efficiency. Also, A. lampa and L. cuneifolia presented higher nitrogen content under water stress conditions. In conclusion, some desert shrubs (A. lampa and C. atamisquea) were able to take advantage of increased nitrogen availability producing more biomass. Understanding seedlings response to nitrogen and water availability on arid lands is critically important to develop adequate revegetation techniques of degraded areas.     

Geometric morphometric analysis of <Emphasis Type="Italic">Setaria italica</Emphasis> (L.) P. Beauv. (foxtail millet) and <Emphasis Type="Italic">Brachiaria ramosa</Emphasis> (L.) Stapf. (browntop millet) and its implications for understanding the biogeography of small millets

Setaria italica (L.) P. Beauv. (foxtail millet) was originally domesticated in northern China. The time and route of its introduction into South Asia is currently unclear due to the possible confusion with autochthonous Brachiaria ramosa (L.) Stapf. (browntop millet). Geometric morphometrics (GM) offer an alternative to traditional archaeobotanical methods to distinguish between these two small millet species. This study aims at finding a method to securely distinguish among charred caryopses of S. italica and B. ramosa, testing its validity on archaeobotanical assemblages and proposing a new approach for studying the dispersion of S. italica throughout Eurasia. Modern S. italica (n = 35) and B. ramosa (n = 34) caryopses and 15 archaeological specimens from a 5th millennium bp archaeological occupation site in northwestern India were analysed. Archaeological and modern caryopses (before and after charring) were photographed with a Leica EZ4D stereoscope, and TPSdig software was used to scale the photographs and manually apply a configuration of three landmarks and six semi-landmarks onto the contours of the embryos. Multivariate statistics were carried out to analyse the shape differences between modern S. italica and B. ramosa and to classify the archaeological specimens. The results show that the shape of the embryo of both species can be clearly distinguished using a GM-approach, both before and after charring. However, charring tends to smooth the shape differences between the two groups, which may affect the interpretation of archaeobotanical assemblages. The comparison between modern and archaeological caryopses suggests that S. italica was not present in northwestern India during the 5th millennium bp.     

Crop rotation associating a legume and the nickel hyperaccumulator <Emphasis Type="Italic">Alyssum murale</Emphasis> improves the structure and biofunctioning of an ultramafic soil

Nickel (Ni) agromining aims to phytoextract heavy metals using hyperaccumulators whilst at the same time rehabilitating ultramafic soils. After removing the bioavailable metal, ultramafic soils are improved in terms of their agronomic properties with the aim of future agricultural uses. The low fertility of ultramafic soils can be compensated by integrating legumes already used in traditional agro-systems because of their importance in soil nitrogen enrichment. However, few studies have evaluated the potential profits of legumes on Ni agromining and their potential benefits on soil biological fertility. Here, we characterized the effect of a crop rotation with two plants, a legume (Vicia sativa) and a hyperaccumulator (Alyssum murale), on the phytoextraction efficiency and on soil structure and biofunctioning. A pot experiment was set up in controlled conditions to grow A. murale and four treatments were tested: rotation with V. sativa (Ro), fertilized mono-culture (FMo), non-fertilized mono-culture (NFMo) and bare soil without plants (BS). No significant difference was found between the Ro and NFMo treatments for the dry biomass yield. However, the Ro treatment showed the highest Ni concentrations ([Ni]) in A. murale shoots compared to FMo and NFMo treatments. The Ro treatment plants had more than twice as many leaves [Ni] compared to FMo. Soil physico-chemical analyses showed that the Ro treatment was better structured and showed the highest presence of bacterial micro-aggregates, as well as less non-aggregated particles. Legumes integration in Ni-agromining systems could be a pioneering strategy to reduce chemical inputs and to improve soil biofunctioning and thus fertility.     

Genetic and phenotypic characterizations of <Emphasis Type="Italic">Xenorhabdus</Emphasis> species (Enterobacteriales: Enterobacteriaceae) isolated from steinernematid nematodes (Rhabditida: Steinernematidae) in Japan

The bacterial species of the genus Xenorhabdus in the family Enterobacteriaceae have a mutualistic association with steinernematid entomopathogenic nematodes (EPNs), which have been used as biological control agents against soil insect pests. In this study we present the genetic and phenotypic characterizations of the Xenorhabdus species isolated from steinernematid nematodes in Japan. The 18 Japanese Xenorhabdus isolates were classified into five bacterial species based on 16S ribosomal RNA (16S rRNA) gene sequences: Xenorhabdus bovienii, Xenorhabdus hominickii, Xenorhabdus indica, Xenorhabdus ishibashii, and Xenorhabdus japonica. There was no genetic variation between the 16S RNA sequences among the three X. ishibashii isolates, 0–0.1% variation among the five X. hominickii isolates, and 0–0.5% among the eight X. bovienii isolates. Phenotypic characterization demonstrated that representative isolates of the five bacterial species shared common characteristics of the genus Xenorhabdus, and only X. hominickii isolates produced indole. Symbiotic association and co-speciation of Xenorhabdus bacteria with Steinernema nematodes from Japan are discussed.     

Identification of the di-<Emphasis Type="Italic">n</Emphasis>-butyl phthalate-biodegrading strains and the biodegradation pathway in strain LMB-1

DNA isolated from a greenhouse soil (Nanjing, Jiangsu Province, China) was suitable for PCR amplification of gene segment coding for the 16S rRNA. Diverse PCR products were characterized by cloning and sequencing, and analysis of bacterial colonies showed the presence over 26 phyla. The most bacteria belonged to Proteobacteria, Actinobacteria, Gemmatimonadetes, Acidobacteria and Planctomycetes. Furthermore, after the enrichment procedure of DBP-degrading microorganisms, 4 strains were isolated from the soil sample with di-n-butyl phthalate (DBP) biodegradability, and they were identified to be Rhizobium sp., Streptomyces sp., Pseudomonas sp. and Acinetobacter sp. Analysis of the degradation products by LC-MS led to identification of metabolites of DBP in strain LMB-1 (identified as Rhizobium sp.) which suggests that DBP was degraded through β-oxidation, demethylation, de-esterification and cleavage of aromatic ring.