Methylobacterium gossipiicola sp. nov., a pink-pigmented, facultatively methylotrophic bacterium isolated from the cotton phyllosphere

Methylotrophic bacteria from rice paddy soils: mineral-nitrogen-utilizing isolates richness in bulk soil and rhizosphere

Methanol, the second most abundant volatile organic compound, primarily released from plants, is a major culprit disturbing atmospheric chemistry. Interestingly, ubiquitously found methanol-utilizing bacteria, play a vital role in mitigating atmospheric methanol effects. Despite being extensively characterized, the effect of nitrogen sources on the richness of methanol-utilizers in the bulk soil and rhizosphere is largely unknown. Therefore, the current study was planned to isolate, characterize and explore the richness of cultivable methylotrophs from the bulk soil and rhizosphere of a paddy field using media with varying nitrogen sources. Our data revealed that more genera of methylotrophs, including Methylobacterium, Ancylobacter, Achromobacter, Xanthobacter, Moraxella, and Klebsiella were enriched with the nitrate-based medium compared to only two genera, Hyphomicrobium and Methylobacterium, enriched with the ammonium-based medium. The richness of methylotrophic bacteria also differed substantially in the bulk soil as compared to the rhizosphere. Growth characterization revealed that majority of the newly isolated methanol-utilizing strains in this study exhibited better growth at 37 °C instead of 30 or 45 °C. Moreover, Hyphomicrobium sp. FSA2 was the only strain capable of utilizing methanol even at elevated temperature 45 °C, showing its adaptability to a wide range of temperatures. Differential carbon substrate utilization profiling revealed the facultative nature of all isolated methanol-utilizer strains with Xanthobacter sp. TS3, being an important methanol-utilizer capable of degrading toxic compounds such as acetone and ethylene glycol. Overall, our study suggests the role of nutrients and plant-microbial interaction in shaping the composition of methanol-utilizers in terrestrial environment.

Impact of glyphosate and glyphosate-based herbicides on phyllospheric Methylobacterium

Symbiotic Methylobacterium comprise a significant portion of the phyllospheric microbiome, and are known to benefit host plant growth, development, and confer tolerance to stress factors. The near ubiquitous use of the broad-spectrum herbicide, glyphosate, in farming operations globally has necessitated a more expansive evaluation of the impacts of the agent itself and formulations containing glyphosate on important components of the plant phyllosphere, including Methylobacterium.This study provides an investigation of the sensitivity of 18 strains of Methylobacterium to glyphosate and two commercially available glyphosate-based herbicides (GBH). Nearly all strains of Methylobacterium showed signs of sensitivity to the popular GBH formulations WeatherMax® and Transorb® in a modified Kirby Bauer experiment. However, exposure to pure forms of glyphosate did not show a significant effect on growth for any strain in both the Kirby Bauer test and in liquid broth, until polysorbate-20 (Tween20) was added as a surfactant. Artificially increasing membrane permeability through the introduction of polysorbate-20 caused a 78-84% reduction in bacterial cell biomass relative to controls containing glyphosate or high levels of surfactant only (0-9% and 6-37% reduction respectively). Concentrations of glyphosate as low as 0.05% w/v (500 µg/L) from both commercial formulations tested, inhibited the culturability of Methylobacterium on fresh nutrient-rich medium.To better understand the compatibility of important phyllospheric bacteria with commercial glyphosate-based herbicides, this study endeavours to characterize sensitivity in multiple strains of Methylobacterium, and explore possible mechanisms by which toxicity may be induced.

Spatio-Temporal Variation in the Phyllospheric Microbial Biodiversity of Alternaria Alternata-Infected Tobacco Foliage

Phyllospheric microbial composition of tobacco (Nicotiana tabacum L.) is contingent upon certain factors, such as the growth stage of the plant, leaf position, and cultivar and its geographical location, which influence, either directly or indirectly, the growth, overall health, and production of the tobacco plant. To better understand the spatiotemporal variation of the community and the divergence of phyllospheric microflora, procured from healthy and diseased tobacco leaves infected by Alternaria alternata, the current study employed microbe culturing, high-throughput technique, and BIOLOG ECO. Microbe culturing resulted in the isolation of 153 culturable fungal isolates belonging to 33 genera and 99 bacterial isolates belonging to 15 genera. High-throughput sequencing revealed that the phyllosphere of tobacco was dominantly colonized by Ascomycota and Proteobacteria, whereas, the most abundant fungal and bacterial genera were Alternaria and Pseudomonas. The relative abundance of Alternaria increased in the upper and middle healthy groups from the first collection time to the third, whereas, the relative abundance of Pseudomonas, Sphingomonas, and Methylobacterium from the same positions increased during gradual leaf aging. Non-metric multi-dimensional scaling (NMDs) showed clustering of fungal communities in healthy samples, while bacterial communities of all diseased and healthy groups were found scattered. FUNGuild analysis, from the first collection stage to the third one in both groups, indicated an increase in the relative abundance of Pathotroph-Saprotroph, Pathotroph-Saprotroph-Symbiotroph, and Pathotroph-Symbiotroph. Inclusive of all samples, as per the PICRUSt analysis, the predominant pathway was metabolism function accounting for 50.03%. The average values of omnilog units (OUs) showed relatively higher utilization rates of carbon sources by the microbial flora of healthy leaves. According to the analysis of genus abundances, leaf growth and leaf position were the important drivers of change in structuring the microbial communities. The current findings revealed the complex ecological dynamics that occur in the phyllospheric microbial communities over the course of a spatiotemporal varying environment with the development of tobacco brown spots, highlighting the importance of community succession.

Comprehensive Comparative Genomics and Phenotyping of Methylobacterium Species

The pink-pigmented facultative methylotrophs (PPFMs), a major bacterial group found in the plant phyllosphere, comprise two genera: Methylobacterium and Methylorubrum. They have been separated into three major clades: A, B (Methylorubrum), and C. Within these genera, however, some species lack either pigmentation or methylotrophy, which raises the question of what actually defines the PPFMs. The present study employed a comprehensive comparative genomics approach to reveal the phylogenetic relationship among the PPFMs and to explain the genotypic differences that confer their different phenotypes. We newly sequenced the genomes of 29 relevant-type strains to complete a dataset for almost all validly published species in the genera. Through comparative analysis, we revealed that methylotrophy, nitrate utilization, and anoxygenic photosynthesis are hallmarks differentiating the PPFMs from the other Methylobacteriaceae. The Methylobacterium species in clade A, including the type species Methylobacterium organophilum, were phylogenetically classified into six subclades, each possessing relatively high genomic homology and shared phenotypic characteristics. One of these subclades is phylogenetically close to Methylorubrum species; this finding led us to reunite the two genera into a single genus Methylobacterium. Clade C, meanwhile, is composed of phylogenetically distinct species that share relatively higher percent G+C content and larger genome sizes, including larger numbers of secondary metabolite clusters. Most species of clade C and some of clade A have the glutathione-dependent pathway for formaldehyde oxidation in addition to the H₄MPT pathway. Some species cannot utilize methanol due to their lack of MxaF-type methanol dehydrogenase (MDH), but most harbor an XoxF-type MDH that enables growth on methanol in the presence of lanthanum. The genomes of PPFMs encode between two and seven (average 3.7) genes for pyrroloquinoline quinone-dependent alcohol dehydrogenases, and their phylogeny is distinctly correlated with their genomic phylogeny. All PPFMs were capable of synthesizing auxin and did not induce any immune response in rice cells. Other phenotypes including sugar utilization, antibiotic resistance, and antifungal activity correlated with their phylogenetic relationship. This study provides the first inclusive genotypic insight into the phylogeny and phenotypes of PPFMs.

Methylobacterium, a major component of the culturable bacterial endophyte community of wild Brassica seed

BACKGROUND

Plants are commonly colonized by a wide diversity of microbial species and the relationships created can range from mutualistic through to parasitic. Microorganisms that typically form symptomless associations with internal plant tissues are termed endophytes. Endophytes associate with most plant species found in natural and managed ecosystems. They are extremely important plant partners that provide improved stress tolerance to the host compared with plants that lack this symbiosis. Plant domestication has reduced endophyte diversity and therefore the wild relatives of many crop species remain untapped reservoirs of beneficial microbes. Brassica species display immense diversity and consequently provide the greatest assortment of products used by humans from a single plant genus important for agriculture, horticulture, bioremediation, medicine, soil conditioners, composting crops, and in the production of edible and industrial oils. Many endophytes are horizontally transmitted, but some can colonize the plant's reproductive tissues, and this gives these symbionts an efficient mechanism of propagation via plant seed (termed vertical transmission).

METHODS

This study surveyed 83 wild and landrace Brassica accessions composed of 14 different species with a worldwide distribution for seed-originating bacterial endophytes. Seed was stringently disinfected, sown within sterile tissue culture pots within a sterile environment and incubated. After approximately 1-month, direct isolation techniques were used to recover bacterial endophytes from roots and shoots of symptomless plants. Bacteria were identified based on the PCR amplification of partial 16S rDNA gene sequences and annotated using the BLASTn program against the NCBI rRNA database. A diversity index was used as a quantitative measure to reflect how many different bacterial species there were in the seed-originating microbial community of the Brassica accessions sampled.

RESULTS

Bacterial endophytes were recovered from the majority of the Brassica accessions screened. 16S rDNA gene sequencing identified 19 different bacterial species belonging to three phyla, namely Actinobacteria, Firmicutes and Proteobacteria with the most frequently isolated species being Methylobacterium fujisawaense, Stenotrophomonas rhizophila and Pseudomonas lactis. Methylobacterium was the dominant genus composing 56% of the culturable isolated bacterial community and was common in 77% of accessions possessing culturable bacterial endophytes. Two selected isolates of Methylobacterium significantly promoted plant growth when inoculated into a cultivar of oilseed rape and inhibited the growth of the pathogen Leptosphaeria maculans in dual culture. This is the first report that investigates the seed-originating endophytic microorganisms of wild Brassica species and highlights the Brassica microbiome as a resource for plant growth promoting bacteria and biological control agents.

Draft Genome Sequence of the Psychrotolerant Bacterium Methylobacterium sp. Strain BTF04, Isolated from Freshwater in Antarctica

Methylobacterium sp. strain BTF04, a pink-pigmented psychrotolerant bacterium, was isolated from freshwater on Barton Peninsula, King George Island, Antarctica. Here, we report the assembled draft genome sequence of Methylobacterium sp. strain BTF04.

Methylobacterium crusticola sp. nov., isolated from biological soil crusts

A pink-pigmented, Gram-negative, rod-shaped, obligate aerobic bacterial strain, MIMD6^T, was isolated from biological soil crusts in PR China. Cells grew at 20-37 °C (optimum, 30 °C), at pH 6-8 (optimum, pH 7) and with 0-1 % (w/v) NaCl (optimum, 0 %). Strain MIMD6^T could use methanol or formate as a sole carbon source to grow, and carried methanol dehydrogenase genes mxaF and xoxF, supporting its methylotrophic metabolism. The respiratory quinone was ubiquinone Q-10, the major fatty acids were C_18 : 1ω7c (87.3 %), and the major polar lipids were diphosphatidylglycerol, phosphatidylmonomethylethanolamine, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine, one unknown aminolipid and one unidentified glycolipid. The results of phylogenetic analyses based on the sequences of the 16S rRNA gene, seven housekeeping genes (dnaK, recA, rimO, rpIK, rpmG, rpsR and rpoB) and methanol dehydrogenase genes indicated that strain MIMD6^T formed a phylogenetic linage with members of the genus Methylobacterium. Strain MIMD6^T was most closely related to Methylobacterium isbiliense DSM 17168^T and Methylobacterium nodulans LMG 21967^T with 16S rRNA gene sequence similarities of 95.7 and 95.2 %, respectively. The genomic DNA G+C content calculated via draft genome sequencing was 73.0 mol%. The average nucleotide identity and digital DNA-DNA hybridization values between strain MIMD6^T and the type strains of other Methylobacterium species were 70.7-82.0 and 24.6-30.0 %, respectively. Based on phenotypic, chemotaxonomic and phylogenetic characteristics, strain MIMD6^T represents a novel species of the genus Methylobacterium, for which the name Methylobacterium crusticola sp. nov. is proposed. The type strain is MIMD6^T (=KCTC 52305^T=MCCC 1K01311^T).

Analysis of 1,000+ Type-Strain Genomes Substantially Improves Taxonomic Classification of Alphaproteobacteria

The class Alphaproteobacteria is comprised of a diverse assemblage of Gram-negative bacteria that includes organisms of varying morphologies, physiologies and habitat preferences many of which are of clinical and ecological importance. Alphaproteobacteria classification has proved to be difficult, not least when taxonomic decisions rested heavily on a limited number of phenotypic features and interpretation of poorly resolved 16S rRNA gene trees. Despite progress in recent years regarding the classification of bacteria assigned to the class, there remains a need to further clarify taxonomic relationships. Here, draft genome sequences of a collection of genomes of more than 1000 Alphaproteobacteria and outgroup type strains were used to infer phylogenetic trees from genome-scale data using the principles drawn from phylogenetic systematics. The majority of taxa were found to be monophyletic but several orders, families and genera, including taxa recognized as problematic long ago but also quite recent taxa, as well as a few species were shown to be in need of revision. According proposals are made for the recognition of new orders, families and genera, as well as the transfer of a variety of species to other genera and of a variety of genera to other families. In addition, emended descriptions are given for many species mainly involving information on DNA G+C content and (approximate) genome size, both of which are confirmed as valuable taxonomic markers. Similarly, analysis of the gene content was shown to provide valuable taxonomic insights in the class. Significant incongruities between 16S rRNA gene and whole genome trees were not found in the class. The incongruities that became obvious when comparing the results of the present study with existing classifications appeared to be caused mainly by insufficiently resolved 16S rRNA gene trees or incomplete taxon sampling. Another probable cause of misclassifications in the past is the partially low overall fit of phenotypic characters to the sequence-based tree. Even though a significant degree of phylogenetic conservation was detected in all characters investigated, the overall fit to the tree varied considerably.

Methylobacterium terricola sp. nov., a gamma radiation-resistant bacterium isolated from gamma ray-irradiated soil

A gamma radiation-resistant and pink-pigmented bacterial strain, designated as 17Sr1-39T, was isolated from a gamma ray-irradiated soil sample collected in the Republic of Korea. Cells were Gram-stain-negative, strictly aerobic, flagellated, asporogenous, rod-shaped and methylotrophic. Results of 16S rRNA gene sequence analysis showed that strain 17Sr1-39T was phylogenetically related to Methylobacterium currus PR1016AT (97.3 %), Methylobacterium aquaticum DSM 16371T (97.2 %), Methylobacterium platani PMB02T (97.0 %), Methylobacterium frigidaeris IER25-16T (96.6 %), Methylobacterium terrae 17Sr1-28T (96.6 %) and Methylobacterium organophilum JCM 2833T (93.4 %). The G+C content calculated based on the genome sequence was 70.4 mol%. The average nucleotide identity and in silico DNA–DNA hybridization values between strain 17Sr1-39T and M. currus , M. aquaticum , M. platani , M. frigidaeris , M. terrae and M. organophilum were 77.3–89.9 and 22–38.2 %, respectively. The predominant fatty acids were summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c) and summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c). The predominant quinone was ubiquinone 10 and the major polar lipids were diphosphatidylglycerol, phosphatidylglycerol and phosphatidylethanolamine. Based on the data from phenotypic tests and genotypic differences between strain 17Sr1-39T and its close phylogenetic relatives, strain 17Sr1-39T represented a new species belonging to the genus Methylobacterium , for which the name Methylobacterium terricola sp. nov. (=KACC 52905T=NBRC 112874T) is proposed.

Phyllosphere-associated Methylobacterium: a potential biostimulant for ginger (Zingiber officinale Rosc.) cultivation

Methanol, a by-product associated with plant metabolism, is a substrate for pink pigmented facultative methylotrophs (PPFMs) of phyllosphere. The symbiotic interaction of PPFMs has many desirable effects on plant growth and disease resistance. The present study investigated the potential of native PPFMs for mitigating biotic stress and plant growth promotion in ginger. PPFMs were isolated from ginger phyllosphere by leaf imprint technique and screened against major fungal phytopathogens of ginger viz. Macrophomina phaseolina, Sclerotium rolfsii, Pythium myriotylum, Colletotrichum gloeosporioides and Fusarium oxysporum. Among the 60 PPFMs, IISRGPPFM13 was selected for its highly inhibitory activity against the target pathogens. The isolate was useful for mineral solubility, production of IAA, siderophores and hydrolytic enzymes like cellulase, pectinase, lipase, amylase and chitinase. On in planta experiments revealed that IISRGPPFM13 considerably increased plant growth parameters when the bacterium was applied as soil drenching cum foliar spraying. Methanol utilization potential of the isolate was confirmed by mxaF gene analysis where the sequence showing 95.51% identity towards Methylobacterium platani and M. iners. Further, 16S rRNA gene sequence showing 98.73% identity with M. komagatae 002-079 T (AB252201). This is the first report of its kind that a genus of Methylobacterium with biostimulant potential isolated from the phyllosphere of ginger.

Antimicrobial and Antioxidant Properties of a Bacterial Endophyte, Methylobacterium radiotolerans MAMP 4754, Isolated from Combretum erythrophyllum Seeds

This study reports on the isolation and identification of Methylobacterium radiotolerans MAMP 4754 from the seeds of the medicinal plant, Combretum erythrophyllum, for the purposes of investigating antimicrobial and antioxidant activities from this endophyte. The strain identity was confirmed by 16S rRNA-based phylogeny and Scanning Electron Microscopy (SEM). Ethyl acetate and chloroform (1 : 1 v/v) extracts from the endophyte were tested for antimicrobial and antioxidant activity on a total of 7 bacterial species (3 Gram-positive and 4 Gram-negative) using the standard Minimum Inhibitory Concentration (MIC) protocol and Quantitative Radical Scavenging activity using the 2, 2-diphenyl-1-picrylhydrazyl (DPPH) assay, respectively. The MICs were recorded at 250 μg/mL for B. subtilis ATCC 19659, B. cereus ATCC 1076, E. coli ATCC1053, and 62.5 μg/mL for K. oxytoca ATCC 13182 and M. smegmatis ATCC 21293, while an IC₅₀ of 5.65 μg/mL was recorded with the DPPH assay. Qualitative phytochemical analysis was positive for alkaloids, flavonoids, and steroids. Gas chromatography/mass spectrometry (GC/MS) analysis revealed the presence of 9-octadecene, 2,4-dinitrophenyl acetate, and 2(5H)-furanone, which have been previously reported for the targeted activities. M. radiotolerans MAMP 4754 tested positive for antimicrobial and antioxidant activity and this is linked to the production of plant-derived secondary metabolites by this strain.

Methylobacterium terrae sp. nov., a radiation-resistant bacterium isolated from gamma ray-irradiated soil

A Gram-stain-negative, asporogenous, aerobic rods, motile by means of a single polar flagellum, catalase- and oxidase-positive, methylotrophic bacterium, designated 17Sr1-28^T, was isolated from gamma ray-irradiated soil. The 16S rRNA gene sequence analysis showed that strain 17Sr1-28^T was phylogenetically related to Methylobacterium currus PR1016A^T (96.8%), Methylobacterium platani PMB02^T (96.2%), Methylobacterium aquaticum DSM 16371^T (96.3%), Methylobacterium tarhaniae N4211^T (96.4%), Methylobacterium frigidaeris IER25-16^T (95.8%), and Methylobacterium organophilum JCM 2833^T (92.7%). The G+C content calculated based on genome sequence was 71.6%. The average nucleotide identity and in silico DNA-DNA hybridization values between strain 17Sr1- 28^T and M. currus, M. platani, M. aquaticum, M. tarhaniae, M. frigidaeris, and M. organophilum were 77.7-90.4% and 22-39.6%, respectively. The major fatty acids of strain 17Sr1-28^T were summed feature 8 (C_18:1ω7c and/or C_18:1ω6c), and summed feature 3 (C_16:1ω7c and/or C_16:1ω6c). The predominant quinone was ubiquinone 10 and the major polar lipids were diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, and phosphatidylglycerol. On the basis of the data from phenotypic tests and genotypic differences between strain 17Sr1-28^T and its close phylogenetic relatives, strain 17Sr1-28^T represents a new species belonging to the genus Methylobacterium, for which the name Methylobacterium terrae sp. nov. (= KCTC 52904^T = NBRC 112873^T) is proposed.

Review of the genus Methylobacterium and closely related organisms: a proposal that some Methylobacterium species be reclassified into a new genus, Methylorubrum gen. nov

The genus Methylobacterium, when first proposed by Patt et al. in 1976, was a monospecific genus created to accommodate a single pink pigmented facultatively methylotrophic bacterium. The genus now has over 50 validly published species, however, the percentage 16S rRNA sequence divergence within Methylobacterium questions whether or not they can still be accommodated within one genus. Additionally, several strains are described as belonging to Methylobacterium, but nodulate legumes and in some cases are unable to utilize methanol as a sole carbon source. This study reviews and discusses the current taxonomic status of Methylobacterium. Based on 16S rRNA gene, multi-locus sequence analysis, genomic and phenotypic data, the 52 Methylobacterium species can no longer be retained in one genus. Consequently, a new genus, Methylorubrum gen. nov., is proposed to accommodate 11 species previously held in Methylobacterium. The reclassified species names are proposed as: Methylorubrum aminovorans comb. nov. (type strain TH-15^T=NCIMB 13343^T=DSM 8832^T), Methylorubrum extorquens comb. nov. (type strain NCIMB 9399^T=DSM 1337^T), Methylorubrum podarium comb. nov. (type strain FM4^T=NCIMB 14856^T=DSM 15083^T), Methylorubrum populi comb. nov. (type strain BJ001^T=NCIMB 13946^T=ATCC BAA-705^T), Methylorubrum pseudosasae comb. nov. (type strain BL44^T=ICMP 17622^T=NBRC 105205^T), Methylorubrum rhodesianum comb. nov. (type strain NCIMB 12249^T=DSM 5687^T), Methylorubrum rhodinum comb. nov. (type strain NCIMB 9421^T=DSM 2163^T), Methylorubrum salsuginis comb. nov. (type strain MR^T=NCIMB 14847^T=NCCB 100140^T), Methylorubrum suomiense comb. nov. (type strain F20^T=NCIMB 13778^T=DSM 14458^T), Methylorubrum thiocyanatum comb. nov. (type strain ALL/SCN-P^T=NCIMB 13651^T=DSM 11490^T) and Methylorubrum zatmanii comb. nov. (type strain NCIMB 12243^T=DSM 5688^T). The taxonomic position of several remaining species is also discussed.

Draft Genome Sequence of Methylobacterium radiotolerans Strain MAMP 4754, a Bacterial Endophyte Isolated from Combretum erythrophyllum in South Africa

We announce here the draft genome sequence of Methylobacterium radiotolerans strain MAMP 4754, isolated from the roots of the medicinal plant Combretum erythrophyllumM. radiotolerans has a genome size of 7,389,282 bp with 7,166 genes and a G+C content of 70.5%.

Phylloremediation of Air Pollutants: Exploiting the Potential of Plant Leaves and Leaf-Associated Microbes

Air pollution is air contaminated by anthropogenic or naturally occurring substances in high concentrations for a prolonged time, resulting in adverse effects on human comfort and health as well as on ecosystems. Major air pollutants include particulate matters (PMs), ground-level ozone (O3), sulfur dioxide (SO2), nitrogen dioxides (NO2), and volatile organic compounds (VOCs). During the last three decades, air has become increasingly polluted in countries like China and India due to rapid economic growth accompanied by increased energy consumption. Various policies, regulations, and technologies have been brought together for remediation of air pollution, but the air still remains polluted. In this review, we direct attention to bioremediation of air pollutants by exploiting the potentials of plant leaves and leaf-associated microbes. The aerial surfaces of plants, particularly leaves, are estimated to sum up to 4 × 108 km2 on the earth and are also home for up to 1026 bacterial cells. Plant leaves are able to adsorb or absorb air pollutants, and habituated microbes on leaf surface and in leaves (endophytes) are reported to be able to biodegrade or transform pollutants into less or nontoxic molecules, but their potentials for air remediation has been largely unexplored. With advances in omics technologies, molecular mechanisms underlying plant leaves and leaf associated microbes in reduction of air pollutants will be deeply examined, which will provide theoretical bases for developing leaf-based remediation technologies or phylloremediation for mitigating pollutants in the air.

Variability of Bacterial Communities in the Moth Heliothis virescens Indicates Transient Association with the Host

Microbes associated with insects can confer a wide range of ecologically relevant benefits to their hosts. Since insect-associated bacteria often increase the nutritive value of their hosts' diets, the study of bacterial communities is especially interesting in species that are important agricultural pests. We investigated the composition of bacterial communities in the noctuid moth Heliothis virescens and its variability in relation to developmental stage, diet and population (field and laboratory), using bacterial tag-encoded FLX pyrosequencing of 16S rRNA amplicons. In larvae, bacterial communities differed depending on the food plant on which they had been reared, although the within-group variation between biological replicates was high as well. Moreover, larvae originating from a field or laboratory population did not share any OTUs. Interestingly, Enterococcus sp. was found to be the dominant taxon in laboratory-reared larvae, but was completely absent from field larvae, indicating dramatic shifts in microbial community profiles upon cultivation of the moths in the laboratory. Furthermore, microbiota composition varied strongly across developmental stages in individuals of the field population, and we found no evidence for vertical transmission of bacteria from mothers to offspring. Since sample sizes in our study were small due to pooling of samples for sequencing, we cautiously conclude that the high variability in bacterial communities suggests a loose and temporary association of the identified bacteria with H. virescens.

Variability of Bacterial Communities in the Moth Heliothis virescens Indicates Transient Association with the Host

Microbes associated with insects can confer a wide range of ecologically relevant benefits to their hosts. Since insect-associated bacteria often increase the nutritive value of their hosts' diets, the study of bacterial communities is especially interesting in species that are important agricultural pests. We investigated the composition of bacterial communities in the noctuid moth Heliothis virescens and its variability in relation to developmental stage, diet and population (field and laboratory), using bacterial tag-encoded FLX pyrosequencing of 16S rRNA amplicons. In larvae, bacterial communities differed depending on the food plant on which they had been reared, although the within-group variation between biological replicates was high as well. Moreover, larvae originating from a field or laboratory population did not share any OTUs. Interestingly, Enterococcus sp. was found to be the dominant taxon in laboratory-reared larvae, but was completely absent from field larvae, indicating dramatic shifts in microbial community profiles upon cultivation of the moths in the laboratory. Furthermore, microbiota composition varied strongly across developmental stages in individuals of the field population, and we found no evidence for vertical transmission of bacteria from mothers to offspring. Since sample sizes in our study were small due to pooling of samples for sequencing, we cautiously conclude that the high variability in bacterial communities suggests a loose and temporary association of the identified bacteria with H. virescens.

Biotechnological and agronomic potential of endophytic pink-pigmented methylotrophic Methylobacterium spp

The genus Methylobacterium is composed of pink-pigmented facultative methylotrophic (PPFM) bacteria, which are able to synthesize carotenoids and grow on reduced organic compounds containing one carbon (C1), such as methanol and methylamine. Due to their high phenotypic plasticity, these bacteria are able to colonize different habitats, such as soil, water, and sediment, and different host plants as both endophytes and epiphytes. In plant colonization, the frequency and distribution may be influenced by plant genotype or by interactions with other associated microorganisms, which may result in increasing plant fitness. In this review, different aspects of interactions with the host plant are discussed, including their capacity to fix nitrogen, nodule the host plant, produce cytokinins, auxin and enzymes involved in the induction of systemic resistance, such as pectinase and cellulase, and therefore plant growth promotion. In addition, bacteria belonging to this group can be used to reduce environmental contamination because they are able to degrade toxic compounds, tolerate high heavy metal concentrations, and increase plant tolerance to these compounds. Moreover, genome sequencing and omics approaches have revealed genes related to plant-bacteria interactions that may be important for developing strains able to promote plant growth and protection against phytopathogens.

Methylobacterium pseudosasicola sp. nov. and Methylobacterium phyllostachyos sp. nov., isolated from bamboo leaf surfaces

Two strains of Gram-negative, methylotrophic bacteria, isolated because of their abilities to promote plant growth, were subjected to a polyphasic taxonomic study. The isolates were strictly aerobic, motile, pink-pigmented, facultatively methylotrophic, non-spore-forming rods. The chemotaxonomic characteristics of the isolates included the presence of C18 : 1ω7c as the major cellular fatty acid. The DNA G+C contents of strains BL36T and BL47T were 69.4 and 69.8 mol%, respectively. 16S rRNA gene sequence analysis of strains BL36T and BL47T placed them under the genus Methylobacterium, with the pairwise sequence similarity between them and the type strains of closely related species ranging from 97.2 to 99.0 %. On the basis of their phenotypic and phylogenetic distinctiveness and the results of DNA–DNA hybridization analysis, the isolates represent two novel species within the genus Methylobacterium , for which the names Methylobacterium pseudosasicola sp. nov. (type strain BL36T = NBRC 105203T = ICMP 17621T) and Methylobacterium phyllostachyos sp. nov. (type strain BL47T = NBRC 105206T = ICMP 17619T) are proposed.

Prerequisites for amplicon pyrosequencing of microbial methanol utilizers in the environment

The commercial availability of next generation sequencing (NGS) technologies facilitated the assessment of functional groups of microorganisms in the environment with high coverage, resolution, and reproducibility. Soil methylotrophs were among the first microorganisms in the environment that were assessed with molecular tools, and nowadays, as well with NGS technologies. Studies in the past years re-attracted notice to the pivotal role of methylotrophs in global conversions of methanol, which mainly originates from plants, and is involved in oxidative reactions and ozone formation in the atmosphere. Aerobic methanol utilizers belong to Bacteria, yeasts, Ascomycota, and molds. Numerous bacterial methylotrophs are facultatively aerobic, and also contribute to anaerobic methanol oxidation in the environment, whereas strict anaerobic methanol utilizers belong to methanogens and acetogens. The diversity of enzymes catalyzing the initial oxidation of methanol is considerable, and comprises at least five different enzyme types in aerobes, and one in strict anaerobes. Only the gene of the large subunit of pyrroloquinoline quinone (PQQ)-dependent methanol dehydrogenase (MDH; mxaF) has been analyzed by environmental pyrosequencing. To enable a comprehensive assessment of methanol utilizers in the environment, new primers targeting genes of the PQQ MDH in Methylibium (mdh2), of the nicotinamide adenine dinucleotide-dependent MDH (mdh), of the methanol oxidoreductase of Actinobacteria (mdo), of the fungal flavin adenine nucleotide-dependent alcohol oxidase (mod1, mod2, and homologs), and of the gene of the large subunit of the methanol:corrinoid methyltransferases (mtaC) in methanogens and acetogens need to be developed. Combined stable isotope probing of nucleic acids or proteins with amplicon-based NGS are straightforward approaches to reveal insights into functions of certain methylotrophic taxa in the global methanol cycle.

Methylobacterium haplocladii sp. nov. and Methylobacterium brachythecii sp. nov., isolated from bryophytes

Pink-pigmented, facultatively methylotrophic bacteria, strains 87eT and 99bT, were isolated from the bryophytes Haplocladium microphyllum and Brachythecium plumosum, respectively. The cells of both strains were Gram-reaction-negative, motile, non-spore-forming rods. On the basis of 16S rRNA gene sequence similarity, strains 87eT and 99bT were found to be related to Methylobacterium organophilum ATCC 27886T (97.1 % and 97.7 %, respectively). Strains 87eT and 99bT showed highest 16S rRNA gene similarity to Methylobacterium gnaphalii 23eT (98.3 and 99.0 %, respectively). The phylogenetic similarities to all other species of the genus Methylobacterium with validly published names were less than 97 %. Major cellular fatty acids of both strains were C18 : 1ω7c and C18 : 0. The results of DNA–DNA hybridization, phylogenetic analyses based on 16S rRNA and cpn60 gene sequences, fatty acid profiles, whole-cell matrix-assisted, laser-desorption/ionization time-of-flight mass spectrometry (MALDI-TOF/MS) analysis, and physiological and biochemical tests allowed genotypic and phenotypic differentiation of strains 87eT and 99bT from their phylogenetically closest relatives. We propose that strains 87eT and 99bT represent novel species within the genus Methylobacterium , for which the names Methylobacterium haplocladii sp. nov. (type strain 87eT = DSM 24195T = NBRC 107714T) and Methylobacterium brachythecii sp. nov. (type strain 99bT = DSM 24105T = NBRC 107710T) are proposed.

Methylobacterium tarhaniae sp. nov., isolated from arid soil

A reddish-orange-pigmented, Gram-stain-negative, aerobic, facultatively methylotrophic strain, N4211(T), isolated from arid soil, collected from Abuja, Nigeria, was analysed by using a polyphasic approach. Phylogenetic analysis, based on 16S rRNA gene sequences, showed that strain N4211(T) belonged to the genus Methylobacterium. Strain N4211(T) was most closely related to Methylobacterium aquaticum GR16(T) (98.56 %), Methylobacterium platani PMB02(T) (97.95 %) and Methylobacterium variabile GR3(T) (97.2 %), and the phylogenetic similarities to all other species of the genus Methylobacterium with validly published names were less than 97.0 %. The major ubiquinones detected were Q-10. The major fatty acids were summed feature 7 (C18 : 1 cis11/t9/t6). The DNA G+C content was 67.3 mol%. DNA-DNA relatedness of strain N4211(T) and the most closely related strains M. aquaticum DSM 16371(T) and M. platani KCTC 12901(T) were 60.0 and 48.2 %, respectively. On the basis of phenotypic, phylogenetic and DNA-DNA hybridization data, strain N4211(T) is assigned to a novel species of the genus Methylobacterium for which the name Methylobacterium tarhaniae sp. nov. is proposed. The type strain is N4211(T)( = KCTC 23615(T) = DSM 25844(T)).

Analysis of 16S rRNA and mxaF genes revealing insights into Methylobacterium niche-specific plant association

The genus Methylobacterium comprises pink-pigmented facultative methylotrophic (PPFM) bacteria, known to be an important plant-associated bacterial group. Species of this group, described as plant-nodulating, have the dual capacity of producing cytokinin and enzymes, such as pectinase and cellulase, involved in systemic resistance induction and nitrogen fixation under specific plant environmental conditions. The aim hereby was to evaluate the phylogenetic distribution of Methylobacterium spp. isolates from different host plants. Thus, a comparative analysis between sequences from structural (16S rRNA) and functional mxaF (which codifies for a subunit of the enzyme methanol dehydrogenase) ubiquitous genes, was undertaken. Notably, some Methylobacterium spp. isolates are generalists through colonizing more than one host plant, whereas others are exclusively found in certain specific plant-species. Congruency between phylogeny and specific host inhabitance was higher in the mxaF gene than in the 16S rRNA, a possible indication of function-based selection in this niche. Therefore, in a first stage, plant colonization by Methylobacterium spp. could represent generalist behavior, possibly related to microbial competition and adaptation to a plant environment. Otherwise, niche-specific colonization is apparently impelled by the host plant.

Methylobacterium gnaphalii sp. nov., isolated from leaves of Gnaphalium spicatum

A pink-pigmented, facultatively methylotrophic bacterium, strain 23e(T), was isolated from the leaves of Gnaphalium spicatum (cudweed). The cells of strain 23e(T) were Gram-reaction negative, motile and non-spore-forming rods. On the basis of 16S rRNA gene sequence similarities, strain 23e(T) was related to Methylobacterium organophilum ATCC 27886(T) (97.1%) and Methylobacterium marchantiae JT1(T) (97%), and the phylogenetic similarities to all other Methylobacterium species with validly published names were less than 97%. Major cellular fatty acids were C(18:1)ω7c, C(16:00) and C(18:0). The results of DNA-DNA hybridization, phylogenetic analyses based on 16S rRNA and cpn60 gene sequences, fatty acid profiles, whole-cell matrix-assisted laser desorption/ionization time of flight/MS analysis, physiological and biochemical tests allowed genotypic and phenotypic differentiation of strain 23e(T) from the phylogenetically closest relatives. We propose that strain 23e(T) represents a novel species within the genus Methylobacterium, for which the name Methylobacterium gnaphalii sp. nov. is proposed. The type strain is 23e(T) (=DSM 24027(T)=NBRC 107716(T)).

Methylobacterium oxalidis sp. nov., isolated from leaves of Oxalis corniculata

A pink-pigmented, facultatively methylotrophic bacterium, strain 35a(T), was isolated from the leaves of Oxalis corniculata. Cells of strain 35a(T) were Gram-reaction-negative, motile, non-spore-forming rods. The highest 16S rRNA gene pairwise sequence similarities for strain 35a(T) were found with the strains of Methylobacterium iners 5317S-33(T) (96.7%), 'Methylobacterium soli' YIM 48816 (96.6%) and Methylobacterium jeotgali S2R03-9(T) (96.3%). 16S rRNA gene sequence similarities with the type strains of all other recognized species of the genus Methylobacterium were below 96%. Major cellular fatty acids were C(18:1)ω7c, C(18:0) and C(16:0). The results of DNA-DNA hybridization experiments, analysis of cpn60 gene sequences, fatty acid profiles, whole-cell MALDI-TOF/MS spectral pattern analysis, and physiological and biochemical tests allowed genotypic and phenotypic differentiation of strain 35a(T) from its nearest phylogenetic neighbours. Strain 35a(T) is therefore considered to represent a novel species within the genus Methylobacterium, for which the name Methylobacterium oxalidis sp. nov. is proposed. The type strain is 35a(T) (=DSM 24028(T)=NBRC 107715(T)).