Phylogenomic analyses and reclassification of the Mesorhizobium complex: proposal for 9 novel genera and reclassification of 15 species.

BACKGROUD: The genus Mesorhizobium is shown by phylogenomics to be paraphyletic and forms part of a complex that includes the genera Aminobacter, Aquamicrobium, Pseudaminobacter and Tianweitania. The relationships for type strains belong to these genera need to be carefully re-evaluated. RESULTS: The relationships of Mesorhizobium complex are evaluated based on phylogenomic analyses and overall genome relatedness indices (OGRIs) of 61 type strains. According to the maximum likelihood phylogenetic tree based on concatenated sequences of 539 core proteins and the tree constructed using the bac120 bacterial marker set from Genome Taxonomy Database, 65 type strains were grouped into 9 clusters. Moreover, 10 subclusters were identified based on the OGRIs including average nucleotide identity (ANI), average amino acid identity (AAI) and core-proteome average amino acid identity (cAAI), with AAI and cAAI showing a clear intra- and inter-(sub)cluster gaps of 77.40-80.91% and 83.98-86.16%, respectively. Combined with the phylogenetic trees and OGRIs, the type strains were reclassified into 15 genera. This list includes five defined genera Mesorhizobium, Aquamicrobium, Pseudaminobacter, Aminobacterand Tianweitania, among which 40/41 Mesorhizobium species and one Aminobacter species are canonical legume microsymbionts. The other nine (sub)clusters are classified as novel genera. Cluster III, comprising symbiotic M. alhagi and M. camelthorni, is classified as Allomesorhizobium gen. nov. Cluster VI harbored a single symbiotic species M. albiziae and is classified as Neomesorhizobium gen. nov. The remaining seven non-symbiotic members were proposed as: Neoaquamicrobium gen. nov., Manganibacter gen. nov., Ollibium gen. nov., Terribium gen. nov., Kumtagia gen. nov., Borborobacter gen. nov., Aerobium gen. nov.. Furthermore, the genus Corticibacterium is restored and two species in Subcluster IX-1 are reclassified as the member of this genus. CONCLUSION: The Mesorhizobium complex are classified into 15 genera based on phylogenomic analyses and OGRIs of 65 type strains. This study resolved previously non-monophyletic genera in the Mesorhizobium complex.

Soluble humic acid suppresses plant immunity and ethylene to promote soybean nodulation.

Symbiotic nitrogen fixation (SNF) is a crucial process for nitrogen geochemical cycling and plant-microbe interactions. Water-soluble humic acid (WSHM), an active component of soil humus, has been shown to promote SNF in the legume-rhizobial symbiosis, but its molecular mechanism remains largely unknown. To reveal the SNF-promoting mechanism, we conducted transcriptomic analysis on soybean treated with WSHM. Our findings revealed that up- and downregulated differentially expressed genes (DEGs) were mainly involved in plant cell-wall/membrane formation and plant defence/immunity in the early stage, while the late stage was marked by the flavonoid synthesis and ethylene biosynthetic process. Further study on representative DEGs showed that WSHM could inhibit GmBAK1d-mediated immunity and BR signalling, thereby promoting rhizobial colonisation, infection, and nodulation, while not favoring pathogenic bacteria colonisation on the host plant. Additionally, we also found that the ethylene pathway is necessary for promoting the soybean nodulation by WSHM. This study not only provides a significant advance in our understanding of the molecular mechanism of WSHM in promoting SNF, but also provides evidence of the beneficial interactions among the biostimulator, host plant, and soil microbes, which have not been previously reported.

Impacts of maize hybrids with different nitrogen use efficiency on root-associated microbiota based on distinct rhizosphere soil metabolites.

Plant genotypes shape root-associated microbiota that affect plant nutrient acquisition and productivity. It is unclear how maize hybrids modify root-associated microbiota and their functions and relationship with nitrogen use efficiency (NUE) by regulating rhizosphere soil metabolites. Here, two N-efficient (NE) (ZD958, DMY3) and two N-inefficient (NIE) maize hybrids (YD9953, LY99) were used to investigate this issue under low N (60 kg N ha-1 , LN) and high N (180 kg N ha-1 , HN) field conditions. NE hybrids had higher yield than NIE hybrids under LN but not HN. NE and NIE hybrids recruited only distinct root-associated bacterial microbiota in LN. The bacterial network stability was stronger in NE than NIE hybrids. Compared with NIE hybrids, NE hybrids recruited more bacterial taxa that have been described as plant growth-promoting rhizobacteria (PGPR), and less related to denitrification and N competition; this resulted in low N2 O emission and high rhizosphere NO3 - -N accumulation. NE and NIE hybrids had distinct rhizosphere soil metabolite patterns, and their specific metabolites were closely related to microbiota and specific genera under LN. Our findings reveal the relationships among plant NUE, rhizosphere soil metabolites, root-associated microbiota, and soil nutrient cycling, and this information is informative for breeding NE crops.

Chelativorans petroleitrophicus sp. nov., a paraffin oil-degrading bacterium isolated from a mixture of oil-based drill cuttings and paddy soil.

We isolated a paraffin oil-degrading bacterial strain from a mixture of oil-based drill cutting and paddy soil, and characterized the strain using a polyphasic approach. The Gram-positive, aerobic, rod-shaped and non-spore-forming strain (SCAU 2101T) grew optimally at 50 °C, pH 7.0 and 0.5 % (w/v) NaCl. Phylogenetic analysis based on 16S rRNA gene sequence indicated that the strain represented a distinct clade in the genus Chelativorans, neighbouring Chelativorans intermedius LMG 28482T (97.1 %). The genome size and DNA G+C content of the strain were 3 969 430 bp and 63.1 mol%, respectively. Whole genome based phylogenomic analyses showed that the average nucleotide identity and digital DNA-DNA hybridization values between strain SCAU 2101T and C. intermedius LMG 28482T were 77.5 and 21.2 %, respectively. The major respiratory quinone was Q-10. The dominant fatty acids were C19 : 0 cyclo ω8c (50.6 %), summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c; 22.5 %) and C18 : 0 (13.8 %). The polar lipids of the strain included phosphatidylethanolamine, phosphatidylmonomethylethanolamine, phosphatidylglycerol, phosphatidylcholine and diphosphatidylglycerol. Based on the results, strain SCAU 2101T was considered to represent a novel species in the genus Chelativorans, for which the name Chelativorans petroleitrophicus sp. nov. is proposed. The type strain is SCAU 2101T (= CCTCC AB 2021125T=KCTC 92067T).

Arachis hypogaea L. from Acid Soils of Nanyang (China) Is Frequently Associated with Bradyrhizobium guangdongense and Occasionally with Bradyrhizobium ottawaense or Three Bradyrhizobium Genospecies.

Henan Province is a major area of peanut production in China but the rhizobia nodulating the crop in this region have not been described. A collection of 217 strains of peanut rhizobia was obtained from six field sites across four soil types in Henan Province, North China, by using peanut as a trap host under glasshouse conditions. The 217 strains separated into 8 distinct types on PCR-RFLP analysis of their IGS sequences. Phylogenetic analysis of the 16S rRNA, recA, atpD, and glnII genes of 11 representative strains of the 8 IGS types identified Bradyrhizobium guangdongense, B. ottawaense and three novel Bradyrhizobium genospecies. Bradyrhizobium guangdongense was dominant, accounting for 75.0% of the total isolates across the field sites while B. ottawaense covered 5.1% and the three novel Bradyrhizobium genospecies 4.1 to 8.8% of the total. The symbiosis-related nodA and nifH gene sequences were not congruent with the core genes on phylogenetic analysis and separated into three groups, two of which were similar to sequences of Bradyrhizobium spp. isolated from peanut in south-east China and the third identical to that of B. yuanmingense isolated from Lespedeza cuneata in northern China. A canonical correlation analysis between the distribution of IGS genotypes and soil physicochemical characteristics and climatic factors indicated that the occurrence of IGS types/species was mainly associated with soil pH and available phosphorus.

Effect of Root Diameter on the Selection and Network Interactions of Root-Associated Bacterial Microbiomes in Robinia pseudoacacia L.

The high plasticity of root morphology, physiology, and function influences root-associated microbiomes. However, the variation in root-associated microbiome diversity and structures in response to root diameter at different root depths remains poorly understood. Here, we selected black locust (Robinia pseudoacacia L.) as a model plant to investigate the selection and network interactions of rhizospheric and root endophytic bacterial microbiomes associated with roots of different diameters (1, 1-2, and > 2 mm) among root depths of 0-100 cm via the Illumina sequencing of the 16S rRNA gene. The results showed that the alpha diversity of the root-associated bacterial communities decreased with increasing root diameters among different root depths; fewer orders with higher relative abundance, especially in the endosphere, were enriched in association with coarse roots (> 2 mm) than fine roots among root depths. Furthermore, the variation in the enriched bacterial orders associated with different root diameters was explained by bulk soil properties. Higher co-occurrence network complexity and stability emerged in the rhizosphere microbiomes of fine roots than those of coarse roots, in contrast to the situation in the endosphere microbiomes. In particular, the endosphere of roots with a diameter of 1-2 mm exhibited the lowest network complexity and stability and a high proportion of keystone taxa (e.g., Cytophagia, Flavobacteriia, Sphingobacteriia, ß-Proteobacteria, and γ-Proteobacteria), suggesting a keystone taxon-reliant strategy in this transitional stage. In summary, this study indicated that root diameter at different root depths differentially affects rhizospheric and endophytic bacterial communities, which implies a close relationship between the bacterial microbiome, root function, and soil properties.

Genomic insight into the origins and evolution of symbiosis genes in Phaseolus vulgaris microsymbionts.

BACKGROUND: Phaseolus vulgaris (common bean) microsymbionts belonging to the bacterial genera Rhizobium, Bradyrhizobium, and Ensifer (Sinorhizobium) have been isolated across the globe. Individual symbiosis genes (e.g., nodC) of these rhizobia can be different within each genus and among distinct genera. Little information is available about the symbiotic structure of indigenous Rhizobium strains nodulating introduced bean plants or the emergence of a symbiotic ability to associate with bean plants in Bradyrhizobium and Ensifer strains. Here, we sequenced the genomes of 29 representative bean microsymbionts (21 Rhizobium, four Ensifer, and four Bradyrhizobium) and compared them with closely related reference strains to estimate the origins of symbiosis genes among these Chinese bean microsymbionts. RESULTS: Comparative genomics demonstrated horizontal gene transfer exclusively at the plasmid level, leading to expanded diversity of bean-nodulating Rhizobium strains. Analysis of vertically transferred genes uncovered 191 (out of the 2654) single-copy core genes with phylogenies strictly consistent with the taxonomic status of bacterial species, but none were found on symbiosis plasmids. A common symbiotic region was wholly conserved within the Rhizobium genus yet different from those of the other two genera. A single strain of Ensifer and two Bradyrhizobium strains shared similar gene content with soybean microsymbionts in both chromosomes and symbiotic regions. CONCLUSIONS: The 19 native bean Rhizobium microsymbionts were assigned to four defined species and six putative novel species. The symbiosis genes of R. phaseoli, R. sophoriradicis, and R. esperanzae strains that originated from Mexican bean-nodulating strains were possibly introduced alongside bean seeds. R. anhuiense strains displayed distinct host ranges, indicating transition into bean microsymbionts. Among the six putative novel species exclusive to China, horizontal transfer of symbiosis genes suggested symbiosis with other indigenous legumes and loss of originally symbiotic regions or non-symbionts before the introduction of common bean into China. Genome data for Ensifer and Bradyrhizobium strains indicated symbiotic compatibility between microsymbionts of common bean and other hosts such as soybean.

Diverse Genomic Backgrounds Vs. Highly Conserved Symbiotic Genes in Sesbania-Nodulating Bacteria: Shaping of the Rhizobial Community by Host and Soil Properties.

Aiming at investigating the overall diversity, biogeography, and symbiosis gene evolutionary history of the Sesbania cannabina-nodulating rhizobia in China, a total of 874 rhizobial isolates originating from the root nodules of this plant grown at different sites were characterized and compared with those of some reference strains. All of the S. cannabina-nodulating rhizobia were classified into 16 (geno) species, including seven novel genospecies in the genera Ensifer, Rhizobium, Neorhizobium, and Agrobacterium, with Ensifer sesbaniae and Neorhizobium huautlense as the dominant and universal species. Ten of these species were found to nodulate other leguminous hosts or to lack nodulating abilities and were defined as symbiovar sesbania. Biogeographic patterns were observed, for which pH, TN, AK, and AP were the main determinants. The effects of pH were opposite to those of TN and AK, while AP presented effects independently of TN, AK, and pH. Symbiotic genes of these rhizobia showed a common origin, but nodA evolved faster than nifH. Point mutation is the main driving force in the evolution of both nodA and nifH, and lateral transfer of symbiotic genes might play an important role in the formation of diverse S. cannabina-nodulating rhizobial species. S. cannabina only nodulates with Sesbania rhizobia, demonstrating its severe selection on rhizobial symbiosis genes. Soil pH and physiochemical characteristics could affect rhizobial survival and competitive nodulation. This study provides insight into the community shifts and evolution of rhizobia in relation to their host and soil environments.

Low-Cost Cellulase-Hemicellulase Mixture Secreted by Trichoderma harzianum EM0925 with Complete Saccharification Efficacy of Lignocellulose.

Fermentable sugars are important intermediate products in the conversion of lignocellulosic biomass to biofuels and other value-added bio-products. The main bottlenecks limiting the production of fermentable sugars from lignocellulosic biomass are the high cost and the low saccharification efficiency of degradation enzymes. Herein, we report the secretome of Trichoderma harzianum EM0925 under induction of lignocellulose. Numerously and quantitatively balanced cellulases and hemicellulases, especially high levels of glycosidases, could be secreted by T. harzianum EM0925. Compared with the commercial enzyme preparations, the T. harzianum EM0925 enzyme cocktail presented significantly higher lignocellulolytic enzyme activities and hydrolysis efficiency against lignocellulosic biomass. Moreover, 100% yields of glucose and xylose were obtained simultaneously from ultrafine grinding and alkali pretreated corn stover. These findings demonstrate a natural cellulases and hemicellulases mixture for complete conversion of biomass polysaccharide, suggesting T. harzianum EM0925 enzymes have great potential for industrial applications.

Aeschynomene indica-Nodulating Rhizobia Lacking Nod Factor Synthesis Genes: Diversity and Evolution in Shandong Peninsula, China.

Aeschynomene indica is a semiaquatic legume that forms both stem and root nodules with rhizobia. Some A. indica rhizobia (AIRs) have been reported to nodulate the host using a Nod factor-independent pathway and possess photosynthetic abilities. To investigate the diversity and community structure of AIRs in China, a total of 300 rhizobial isolates were acquired from the root and stem nodules of A. indica grown at 4 sites in Shandong Peninsula, China. Nineteen representative strains were selected according to their recA phylogeny. With further classification in comparison with reference strains, 10 Bradyrhizobium genospecies were defined based on the 16S rRNA gene phylogeny and multilocus sequence analysis (MLSA) of housekeeping genes (HKGs) recA, atpD, glnII, dnaK, gyrB, and rpoB In addition, 6 genospecies were found only in China. No nodulation gene (nodA, nodB, nodC, or nodZ) was detected in the AIRs isolates by PCR amplification and Southern blotting. Phylogenetic analysis of nifH and the photosynthesis-related gene pufLM revealed their common origins. All representative strains formed root nodules, but only 9 representative strains for 4 genospecies formed stem nodules on A. indica, indicating that the stem nodulation process of A. indica is limited to some strains. The nucleotide diversity and recombination events of the HKGs, as well as nifH and pufLM genes, showed that mutation contributes more than recombination in evolution. The distribution of dominant AIR genospecies was mainly affected by available nitrogen, organic carbon, total nitrogen, and pH. Our study helps to characterize the diversity and evolution of AIRs.IMPORTANCEAeschynomene indica rhizobia (AIRs) can form both root and stem nodules via Nod factor-independent processes, which distinguishes them from other rhizobia. This study systematically uncovered the diversity and community composition of A. indica rhizobia distributed in eastern China. Our results reclassified all the A. indica rhizobia across the world and represent a useful contribution to evaluating the diversity and distribution of the symbiont. The presence of novel genospecies specifically distributed in China enriched the A. indica rhizobia resources and provided insight into the geographic distribution of rhizobia. The phylogenetic relationship between nifH and pufLM of A. indica rhizobia across the world provides insight into the evolution of their nitrogen fixation and photosynthetic abilities.

Rhizobium changzhiense sp. nov., isolated from effective nodules of Vicia sativa L. in North China.

Three fast-growing rhizobial strains isolated from effective nodules of common vetch (Vicia sativa L.) were characterized using a polyphasic approach. All three strains were assigned to the genus Rhizobium on the basis of the results of 16S rRNA gene sequence analysis. Phylogenetic analysis based on concatenated atpD-recA genes separated the strains into a distinct lineage represented by WYCCWR 11279T, which showed average nucleotide identity values of 95.40 and 93.61 % with the most similar phylogenetic type strains of Rhizobium sophorae CCBAU 03386T and Rhizobium laguerreae FB TT, respectively. The digital DNA-DNA hybridization relatedness values between WYCCWR 11279T and the closest related type strains were less than 70 %. Therefore, a novel rhizobial species is proposed, Rhizobium changzhiense sp. nov., and strain WYCCWR 11279T (=HAMBI 3709T=LMG 31534T) is designated as the type strain for the novel species.

Rhizobium chutanense sp. nov., isolated from root nodules of Phaseolus vulgaris in China.

Two Gram-stain-negative, rod-shaped bacterial strains (C5T and C16), isolated from root nodules of Phaseolus vulgaris L. in Jiangxi Province, PR China, were characterized by using a polyphasic taxonomical approach. The phylogenetic analysis of the 16S rRNA gene and three concatenated housekeeping genes (recA-glnII-atpD) revealed that C5T and C16 were members of the genus Rhizobium, yet were distinct from known species. The case for strain C5T representing a novel species was supported by genomic results. Pairwise digital DNA-DNA hybridization and average nucleotide identity values were much lower than the proposed and generally accepted species boundaries. The genome-based phylogenetic tree reconstructed by using the up-to-date bacterial core gene set consisting of 92 genes showed that the strains formed a monophyletic branch, further supporting this result. The symbiotic genes of nodC and nifH were identified in both strains; each could nodulate Phaseolus vulgaris and Glycine max but not Leucaena leucocephala, Pisum sativum or Medicago sativa plants. Major cellular fatty acids of C5T were summed feature 8 (C18 : 1 ω7c/C18 : 1 ω6c; 58.8 %), C18 : 1 ω7c 11-methyl (14.2 %) and C18 : 0 (8.1 %). The DNA G+C content of C5T was 61.4 mol%. Based on these genomic, chemotaxonomic and phenotypic characteristics, we propose a novel species: Rhizobium chutanense sp. nov. The type strain is C5T (=CCTCC AB 2018143T=LMG 30777T).

Comparative analysis of rhizobial chromosomes and plasmids to estimate their evolutionary relationships.

In the present study, complete genomic sequences retrieved from 57 rhizobial strains that covered four genera including 11 species were analyzed comprehensively. The four types of replicons: chromosomes, chromids, nonsymbiotic plasmids, and symbiotic plasmids were investigated and compared among these strains. Results showed that co-evolution occurred among these four replicons based on the similarities in average nucleotide identity. High correlation coefficient r values were observed between chromosomes and chromids, as well as between chromosomes and nonsymbiotic plasmids. Chromosomes and symbiotic plasmids showed different phylogenetic topology based on their core genes. Population structure analyses were performed to extrapolate the evolutionary histories of the test strains based on their chromosomal and symbiotic plasmid background. This resulted in seven ancestral types for chromosomal genes and three ancestral types for symbiotic plasmid genes. Rhizobial strains containing chromosome genes with ancestral type E tend to contain symbiotic plasmid genes with ancestral type II, while rhizobial strains containing chromosome genes with ancestral type G tend to contain symbiotic plasmid genes with ancestral type III. Seventeen strains associated with different host plant species which harbored the symbiotic genes with ancestral type I, exhibited high genetic diversity. In addition, Fu's test of the symbiotic plasmid genes with ancestral type III had undergone an expansion event, implying the influence of negative selection on these symbiotic plasmid genes.

Two cultivated legume plants reveal the enrichment process of the microbiome in the rhizocompartments.

The microbiomes of rhizocompartments (nodule endophytes, root endophytes, rhizosphere and root zone) in soya bean and alfalfa were analysed using high-throughput sequencing to investigate the interactions among legume species, microorganisms and soil types. A clear hierarchical filtration of microbiota by plants was observed in the four rhizocompartments - the nodule endosphere, root endosphere, rhizosphere and root zone - as demonstrated by significant variations in the composition of the microbial community in the different compartments. The rhizosphere and root zone microbial communities were largely influenced by soil type, and the nodule and root endophytes were primarily determined by plant species. Diverse microbes inhabited the root nodule endosphere, and the corresponding dominant symbiotic rhizobia belonged to Ensifer for alfalfa and Ensifer-Bradyrhizobium for soya bean. The nonsymbiotic nodule endophytes were mainly Proteobacteria, Actinobacteria, Firmicutes and Bacteroidetes. The variation in root microbial communities was also affected by the plant growth stage. In summary, this study demonstrated that the enrichment process of nodule endophytes follows a hierarchical filtration and that the bacterial communities in nodule endophytes vary according to the plant species.

Interactions of plant growth-promoting rhizobacteria and soil factors in two leguminous plants.

Although the rhizomicrobiome has been extensively studied, little is known about the interactions between soil properties and the assemblage of plant growth-promoting microbes in the rhizosphere. Herein, we analysed the composition and structure of rhizomicrobiomes associated with soybean and alfalfa plants growing in different soil types using deep Illumina 16S rRNA sequencing. Soil pH, P and K significantly affected the composition of the soybean rhizomicrobiome, whereas soil pH and N had a significant effect on the alfalfa rhizomicrobiome. Plant biomass was influenced by plant species, the composition of the rhizomicrobiome, soil pH, N, P and plant growth stage. The beta diversity of the rhizomicrobiome was the second most influential factor on plant growth (biomass). Rhizomicrobes associated with plant biomass were identified and divided into four groups: (1) positively associated with soybean biomass; (2) negatively associated with soybean biomass; (3) positively associated with alfalfa biomass; and (4) negatively associated with alfalfa biomass. Genera assemblages among the four groups differentially responded to soil properties; Group 1 and Group 2 were significantly correlated with soil pH and P, whereas Group 3 and Group 4 were significantly correlated with soil N, K and C. The influence of soil properties on the relative abundance of plant biomass-associated rhizomicrobes differed between soybean and alfalfa. The results suggest the rhizomicrobiome has a pronounced influence on plant growth, and the rhizomicrobiome assemblage and plant growth-associated microbes are differentially structured by soil properties and leguminous plant species.

Genetic diversity of indigenous soybean-nodulating rhizobia in response to locally-based long term fertilization in a Mollisol of Northeast China.

The influences of five different fertilizer treatments on diversity of rhizobia in soybean nodule were investigated in a long-term experiment with with four replicates: (1) control (without fertilization), (2) balanced NPK fertilizer (NPK), and (3-5) unbalanced chemical fertilizers without one of the major elements (NP, PK, and NK) in Mollisol in Northeast China. The highest soybean yield was observed in the NPK treatment. Total of 200 isolates were isolated and grouped into four Bradyrhizobium genospecies corresponding to B. japonicum, B. diazoefficiens, B. ottawaense and Bradyrhizobium sp. I, based upon the multilocus sequence analysis of 6 housekeeping genes. The Bradyrhizobium sp. I was extensively distributed throughout the study site and was recorded as the dominant soybean rhizobia (82.5-87.5%). Except the NK treatment, the other fertilizer treatments had no effect on rhizobial species composition. Compared with the CK treatment, all the fertilizer treatments decreased species richness, diversity and evenness. The soil organic carbon contents, available N content and pH were the key soil factors to rhizobial community structure. Results suggest that long-term fertilization can decrease rhizobial species diversity, while balanced fertilization with NPK is the most suitable fertilization regime if taking both soybean yields and rhizobial diversity into account.

Syntrophic Interactions Within a Butane-Oxidizing Bacterial Consortium Isolated from Puguang Gas Field in China.

Butane oxidation by the hydrocarbon degradation bacteria has long been described, but little is known about the microbial interaction in this process. To investigate this interaction, the efficiency of butane oxidation was estimated in monocultures and co-cultures of six strains of butane-oxidizing bacteria (BOB) and a butanol-oxidizing strain. Results showed that the butane degradation velocity was at least 26 times higher in the co-culture of the seven strains (228.50 nmol h(-1)) than in the six individual monocultures (8.71 nmol h(-1)). Gas chromatographic analysis of metabolites in the cultures revealed the accumulation of butanol in the monocultures of BOB strains but not in the co-culture with the butanol-oxidizing strain. These results evidenced a novel syntrophic association between BOB and butanol-oxidizing bacteria in the butane oxidation. The BOB strains oxidized butane into butanol, but this activity was inhibited by the accumulated butanol in monocultures, whereas the removal of butanol by the butanol-oxidizing strain in co-culture could eliminate the suppression and improve the butane degradation efficiency. In the co-culture, both BOB and butanol-oxidizing bacteria could grow and the time needed for butane complete removal was shortened from more than 192 h to less than 4 h. The unsuppressed effect of the co-culture was also consistent with the results of reverse transcription quantitative real-time PCR (RT-qPCR) of bmoX gene because increased expression of this gene was detected during the syntrophic growth compared with that in monoculture, pointing to the upregulation of bmoX in the syntrophic interaction.

Comparative Gut Microbiomes of Four Species Representing the Higher and the Lower Termites.

Aiming at learning the association between the gut microbiota and termites with different diet habits and phylogenetic positions, the gut bacteria of three populations for each of the two higher termites (wood-feeding Mironasutitermes shangchengensis and fungus-feeding Odontotermes formosanus) and two wood-feeding lower termites (Tsaitermes ampliceps and Reticulitermes flaviceps) were analyzed by high-throughput 454 pyrosequencing of 16S V1-V3 amplicons. As results, 132 bacterial genera and some unidentified operational taxonomic units within 29 phyla in the gut bacteria were detected, with Spirochaetes (11-55%), Firmicutes (7-18%), Bacteroidetes (7-31%), and Proteobacteria (8-14%) as the main phyla, and Treponema, TG5, Dysgonomonas, Tannerella, za29, Lactococcus, Pseudomonas, and SJA-88 as the common genera in all the four termites. The diversity of gut bacterial communities in the higher termite guts was significantly greater than that in the lower termites; while the gut microbiota in M. shangchengensis (wood-feeding higher termite) was more similar to those of the wood-feeding lower termites rather than that of O. formosanus (fungus-feeding higher termite), and phylum Spirochaetes and nitrogen-fixing bacteria were super-dominant in the wood-feeding termites, despite of their phylogenetic relations. This study reported for the first time the gut bacterial communities for the termites of M. shangchengensis and T. ampliceps and the comparative analyses showed that the gut microbial communities varied according to the phylogeny and the diet habits of termites.