Reclassification of Brevibacterium oxydans (Chatelain and Second 1966) as Microbacterium oxydans comb. nov

Four new Microbacterium species isolated from seaweeds and reclassification of five Microbacterium species with a proposal of Paramicrobacterium gen. nov. under a genome-based framework of the genus Microbacterium

The taxonomic relationships of 10 strains isolated from seaweeds collected from two beaches in Republic of Korea were studied by sequencing and analyses of 16S rRNA genes and whole genomes. For the construction of a more reliable and robust 16S rRNA gene phylogeny, the authentic and nearly complete 16S rRNA gene sequences of all the Microbacterium type strains were selected through pairwise comparison of the sequences contained in several public databases including the List of Prokaryotic names with Standing in Nomenclature (LPSN). The clustering of the ten study strains into five distinct groups was apparent in this single gene-based phylogenetic tree. In addition, the 16S rRNA gene sequences of a few type strains were shown to be incorrectly listed in LPSN. An overall phylogenomic clustering of the genus Microbacterium was performed with a total of 113 genomes by core genome analysis. As a result, nine major (≥ three type strains) and eight minor (two type strains) clusters were defined mostly at gene support index of 92 and mean intra-cluster OrthoANIu of >80.00%. All of the study strains were assigned to a Microbacterium liquefaciens clade and distributed further into four subclusters in the core genome-based phylogenetic tree. In vitro phenotypic assays for physiological, biochemical, and chemotaxonomic characteristics were also carried out with the ten study strains and seven closely related type strains. Comparison of the overall genomic relatedness indices (OGRI) including OrthoANIu and digital DNA-DNA hybridization supported that the study strains constituted four new species of the genus Microbacterium. In addition, some Microbacterium type strains were reclassified as members of preexisting species. Moreover, some of them were embedded in a new genus of the family Microbacteriaceae based on their distinct separation in the core genome-based phylogenetic tree and amino acid identity matrices. Based on the results here, four new species, namely, Microbacterium aurugineum sp. nov., Microbacterium croceum sp. nov., Microbacterium galbinum sp. nov., and Microbacterium sufflavum sp. nov., are described, along with the proposal of Paramicrobacterium gen. nov. containing five reclassified Microbacterium species from the "Microbacterium agarici clade", with Paramicrobacterium agarici gen. nov., comb. nov. as the type species.

Microbial consortia degrade several widely used organic UV filters, but a number of hydrophobic filters remain recalcitrant to biodegradation

Organic UV filters are important ingredients in many personal care products, including sunscreens. Evaluating the biodegradability of organic UV filters is key to estimate their recalcitrance and environmental fate and thus central to their overall environmental risk assessment. In order to further understand the degradation process, the aim was to investigate whether specific consortia could degrade certain UV filters. Several bacterial strains were isolated from enrichment cultures actively degrading octocrylene (OC), butyl methoxydibenzoylmethane (BM), homosalate (HS), and 2-ethylhexyl salicylate (ES) and were utilized to construct an in-house consortium. This synthetic consortium contained 27 bacterial strains and degraded OC, BM, HS, and ES 60-80% after 12 days, but not benzophenone-3 (BP3), methoxyphenyl triazine (BEMT), methylene bis-benzotriazolyl tetramethylbutylphenol (MBBT), diethylhexyl butamido triazone (DBT), ethylhexyl triazone (EHT), or diethylamino hydroxybenzoyl hexyl benzoate (DHHB). Furthermore, several commercial microbial mixtures from Greencell were tested to assess their degradation activity toward the same organic UV filters. ES and HS were degraded by some of the commercial consortia, but to a lesser extent. The rest of the tested UV filters were not degraded by any of the commercial bacterial mixes. These results confirm that some organic UV filters are recalcitrant to biodegradation, while others are degraded by a specific set of microorganisms.

Draft Whole-Genome Sequences of Microbacterium oxydans and Microbacterium maritypicum Strains

Microbacterium spp. are a group of microbes that have been recovered from a wide variety of environments in nature. Here, I report the complete genomic data for Microbacterium oxydans and Microbacterium maritypicum type strains that are already present in public culture repositories. The genome of the M. oxydans strain was 3,894,869 bp long, with a G+C content of 68.26%. The genome of the M. maritypicum strain was 3,668,377 bp long, with a G+C content of 68.44%.

Microbacterium algeriense sp. nov., a novel actinobacterium isolated from Algerian oil production waters

A non-motile, straight-rod-shaped, Gram-stain-positive and facultative anaerobic bacterium (i.e., strain G1^T) was isolated from production waters from an Algerian oilfield. Growth was observed in the presence of 0.3-3.5 % (w/v) NaCl, at 20-50 °C and at pH 6.0-9.0. Results of phylogenetic analyses based on 16S rRNA gene sequences showed that strain G1^T belonged to the genus Microbacterium. Strain G1 ^T was closely related to Microbacterium oxydans (DSM 20578^T) and Microbacterium maritypicum (DSM 12512^T) with 99.8 % sequence similarity and to Microbacterium saperdae (DSM 20169^T) with 99.6 % sequence similarity. Strain G1 ^T contained MK9, MK10, MK11, MK12 and MK13 as respiratory quinones, and phosphatidylglycerol, diphosphatidylglycerol and glycolipid as the major polar lipids. The major cellular fatty acids were anteiso-C_15:0, iso-C_16:0 and anteiso-C_17:0. The estimated DNA G+C content was 69.57 mol% based on its draft genome sequence. Genome annotation of strain G1^T predicted the presence of 3511 genes, of which 3483 were protein-coding and 47 were tRNA genes. The DNA-DNA hybridization (DDH) and average nucleotide identity (ANI) values between strain G1^T and M. oxydans (DSM 20578^T) and M. maritypicum (DSM 12512^T) were in both cases far below the respective species boundary thresholds (27.5 and 28.0 % for DDH; and 84.40 and 84.82% for ANI, respectively). Based on the data presented above, strain G1^T was considered to represent a novel species for which the name Microbacterium algeriense is proposed with the type strain G1^T (=DSM 109018^T=LMG 31276^T).

Adsorption of Tolaasins, the Toxins Behind Mushroom Bacterial Blotch, by Microbacterium spp. is Insufficient for Its Detoxification

Tolaasins are lipodepsipeptides secreted by Pseudomonas tolaasii, the causal agent of bacterial blotch on several kinds of cultivated mushrooms. Our previous study reported on tolaasin detoxification by Microbacterium sp. K3-5 as a potential biocontrol of the disease. In this study, the tolaasin-detoxifying activities of various type strains of Microbacterium spp. were evaluated through chemical and biological assays. The bacterial cells of all tested strains of Microbacterium spp. showed tolaasin I-elimination from liquid phase. However, the toxin activities of tolaasins were still retained on the tolaasin-treated bacterial cells of all Microbacterium strains except M. foliorum NBRC 103072^T. Furthermore, intact tolaasin I was recovered from the tolaasin-treated bacterial cells of all tested strains except M. foliorum NBRC 103072^T. Our data reveal that Microbacterium spp. can be characterized as effective tolaasin I-eliminating bacteria through cell adsorption, but that this adsorption alone is insufficient for actual tolaasin detoxification. The biological degradation process must be needed to carry out the detoxification.

Cuticular bacteria appear detrimental to social spiders in mixed but not monoculture exposure

Much of an animal’s health status, life history, and behavior are dictated by interactions with its endogenous and exogenous bacterial communities. Unfortunately, interactions between hosts and members of their resident bacterial community are often ignored in animal behavior and behavioral ecology. Here, we aim to identify the nature of host–microbe interactions in a nonmodel organism, the African social spider Stegodyphus dumicola. We collected and identified bacteria from the cuticles of spiders in situ and then exposed spiders to bacterial monocultures cultures via topical application or injection. We also topically inoculated spiders with a concomitant “cocktail” of bacteria and measured the behavior of spiders daily for 24 days after inoculation. Lastly, we collected and identified bacteria from the cuticles of prey items in the capture webs of spiders, and then fed spiders domestic crickets which had been injected with these bacteria. We also injected 1 species of prey-borne bacteria into the hemolymph of spiders. Only Bacillus thuringiensis caused increased mortality when injected into the hemolymph of spiders, whereas no bacterial monocultures caused increased mortality when applied topically, relative to control solutions. However, a bacterial cocktail of cuticular bacteria caused weight loss and mortality when applied topically, yet did not detectibly alter spider behavior. Consuming prey injected with prey-borne bacteria was associated with an elongated lifespan in spiders. Thus, indirect evidence from multiple experiments suggests that the effects of these bacteria on spider survivorship appear contingent on their mode of colonization and whether they are applied in monoculture or within a mixed cocktail. We urge that follow-up studies should test these host–microbe interactions across different social contexts to determine the role that microbes play in colony performance.

Efficient production of lumichrome by Microbacterium sp. strain TPU 3598

Lumichrome is a photodegradation product of riboflavin and is available as a photosensitizer and fluorescent dye. To develop new efficient methods of lumichrome production, we isolated bacterial strains with high lumichrome productivity from soil. The strain with highest productivity was identified as Microbacterium sp. strain TPU 3598. Since this strain inductively produced lumichrome when cultivated with riboflavin, we developed two different methods, a cultivation method and a resting cell method, for the production of large amounts of lumichrome using the strain. In the cultivation method, 2.4 g (9.9 mmol) of lumichrome was produced from 3.8 g (10.1 mmol) of riboflavin at the 500-ml scale (98% yield). The strain also produced 4.7 g (19.4 mmol) of lumichrome from 7.6 g (20.2 mmol) of riboflavin (96% yield) by addition of riboflavin during cultivation at the 500-ml scale. In the resting cell method, 20 g of cells (wet weight) in 100 ml of potassium phosphate buffer, pH 7.0, produced 2.4 g of lumichrome from 3.8 g of riboflavin (98% yield). Since the lumichrome production by these methods was carried out in suspension, the resulting lumichrome was easily purified from the cultivation medium or reaction mixture by centrifugation and crystallization. Thus, the biochemical methods we describe here are a significant improvement in terms of simplicity and yield over the existing chemical, photolytic, and other biochemical methods of lumichrome production.

A selective medium for the isolation of Microbacterium species in oral cavities

The genus Microbacterium has been isolated from the environment, dairy goods, and human clinical specimens. Although, in our previous studies, some Microbacterium species were infrequently detected in oral samples collected from humans, there is currently no report that these organisms, which are capable of causing serious systemic infections, were isolated from the human oral cavity. The aim of the present study was to develop a selective medium to isolate the representative Microbacterium species most frequently detected in human clinical specimens, and reveal the distribution of individual Microbacterium species in the oral cavity. The growth recoveries of representative Microbacterium species on the selective medium, designated as MSM, were sufficient. Moreover, the growth of other representative oral bacteria was markedly inhibited on the selective medium. The proportion of Microbacterium species in the saliva samples of 60 subjects, 20 of whom were removable denture wearers, was then examined. The proportion of these organisms was also examined in environmental samples obtained by swabbing 20 washstands. PCR primers were designed for representative Microbacterium species. The genus Microbacterium was detected in 45% of the saliva and denture plaque samples collected from the twenty removable denture wearers, but was absent in the saliva of the forty non-denture wearers. On the other hand, these organisms were detected in all environmental samples. The genus Microbacterium accounted for 0.00003%, 0.0001%, and 12.6% of the total cultivable bacteria number on the BHI medium in the saliva and denture plaque samples of removable denture wearers and in the environmental samples, respectively. The most predominant Microbacterium species in all positive samples was Microbacterium oxydans. These results indicated that the genus Microbacterium was not a part of the normal flora in the human oral cavity, except for subjects wearing dentures that were contaminated by the environment, and the selective medium, designated as MSM, was useful for isolating Microbacterium species, which are frequently encountered in human clinical specimens, from the various samples.

Microbacterium mangrovi sp. nov., an amylolytic actinobacterium isolated from mangrove forest soil

Strain MUSC 115(T) was isolated from mangrove soil of the Tanjung Lumpur river in the state of Pahang, Peninsular Malaysia. Cells of this strain stained Gram-positive and were non-spore-forming, short rods that formed yellowish-white colonies on different agar media. The taxonomy of strain MUSC 115(T) was studied by a polyphasic approach, and the organism showed a range of phylogenetic and chemotaxonomic properties consistent with those of the genus Microbacterium. The cell-wall peptidoglycan was of type B2β, containing the amino acids ornithine, alanine, glycine, glutamic acid and homoserine. The muramic acid was of the N-glycolyl form. The predominant menaquinones detected were MK-12, MK-13 and MK-11. The polar lipids consisted of phosphatidylglycerol, phosphoglycolipid, diphosphatidylglycerol, two unidentified lipids, three unidentified phospholipids and four unidentified glycolipids. The major fatty acids of the cell membrane were anteiso-C15:0 and anteiso-C17:0. The whole-cell sugars detected were ribose, glucose, mannose and galactose. Based on the 16S rRNA gene sequence, strain MUSC 115(T) showed the highest sequence similarity to Microbacterium immunditiarum SK 18(T) (98.1%), M. ulmi XIL02(T) (97.8%) and M. arborescens DSM 20754(T) (97.5%) and lower sequence similarity to strains of other species of the genus Microbacterium. DNA-DNA hybridization experiments revealed a low level of DNA-DNA relatedness (less than 24%) between strain MUSC 115(T) and the type strains of closely related species. Furthermore, BOX-PCR fingerprint comparison also indicated that strain MUSC 115(T) represented a unique DNA profile. The DNA G+C content determined was 70.9 ± 0.7 mol%, which is lower than that of M. immunditiarum SK 18(T). Based on the combination of genotypic and phenotypic data, it is proposed that strain MUSC 115(T) represents a novel species of the genus Microbacterium, for which the name Microbacterium mangrovi sp. nov. is proposed. The type strain is MUSC 115(T) ( = MCCC 1K00251(T) = DSM 28240(T) = NBRC 110089(T)).

Microbacterium sediminis sp. nov., a psychrotolerant, thermotolerant, halotolerant and alkalitolerant actinomycete isolated from deep-sea sediment

An aerobic, rod-shaped, Gram-positive, oxidase- and catalase-positive bacterial isolate, strain YLB-01T, was characterized using phenotypic and molecular taxonomic methods. 16S rRNA gene sequence analysis revealed that the isolate belonged to the genus Microbacterium and represented an evolutionary lineage that was distinct from recognized species of the genus Microbacterium . The isolate showed <97 % 16S rRNA gene sequence similarity with respect to the type strains of all of the members of the genus Microbacterium with validly published names. Cell-wall hydrolysate from the isolate contained the amino acids ornithine, alanine, glycine homoserine and glutamic acid, and the cell-wall sugars consisted of ribose, glucose and galactose. The main respiratory quinones were MK-8, 9, 10 and 11. The major cellular fatty acids were anteiso-C15 : 0 (38.5 %), anteiso-C17 : 0 (23.1 %) and C16 : 0 (18.9 %). The polar lipids contained diphosphatidylglycerol, phosphatidylglycerol, an unidentified phospholipid and two unidentified glycolipids. The DNA G+C content of strain YLB-01T was 71 mol%. On the basis of the morphological, physiological and chemotaxonomic data and the results of comparative 16S rRNA gene sequence analysis, this isolate represents a novel species of the genus Microbacterium , for which the name Microbacterium sediminis sp. nov. is proposed. The type strain is YLB-01T ( = DSM 23767T = CCTCC AB2010363T = MCCC 1A06153T).

Microbacterium neimengense sp. nov., isolated from the rhizosphere of maize

A Gram-positive, non-motile, non-spore-forming, rod-shaped bacterium, strain 7087T, was isolated from rhizosphere of maize in China. The strain grew at 4–50 °C and at pH 4–10, with optima of 37 °C and pH 7.0, respectively. Phylogenetic analysis based on the full-length 16S rRNA gene sequence revealed that strain 7087T was a member of the genus Microbacterium . High levels of 16S rRNA gene similarities were found between strain 7087T and Microbacterium binotii DSM 19164T (99.8 %). However, the DNA–DNA hybridization value between strain 7087T and Microbacterium binotii DSM 19164T was 24.2 %. The DNA G+C content of strain 7087T was 69.9 mol%. The major fatty acids were anteiso-C17 : 0 (36.45 %), anteiso-C15 : 0 (36.08 %) and iso-C16 : 0 (16.11 %). The predominant menaquinones were MK-10 (28.1 %), MK-11 (54.8 %) and MK-12 (17.1 %). The diagnostic diamino acid in the cell-wall peptidoglycan was ornithine. The major polar lipids are diphosphatidylglycerol, unknown phospholipids, an unknown glycolipid and unknown amino lipids. On the basis of these results, strain 7087T is considered to represent a novel species of the genus Microbacterium , for which the name Microbacterium neimengense sp. nov. is proposed. The type strain is 7087T ( = ACCC 03008T = DSM 24985T).

Microbacterium immunditiarum sp. nov., an actinobacterium isolated from landfill surface soil, and emended description of the genus Microbacterium

A Gram-positive, non-endospore-forming bacterium, designated strain SK 18T, was isolated from surface soil of a landfill site by dilution plating on trypticase soy broth agar. Preliminary characterization of strain SK 18T via biochemical tests, analysis of fatty acid methyl esters and partial 16S rRNA gene sequencing placed it within the genus Microbacterium . Analysis of the cell wall indicated that the peptidoglycan was of cross-linkage type B, containing the amino acids lysine and ornithine and with muramic acid in the N-glycolyl form. The polar lipids were phosphatidylglycerol, diphosphatidylglycerol, an unidentified phospholipid and an unidentified glycolipid. The major fatty acids of the cell membrane were anteiso-C17 : 0, anteiso-C15 : 0 and iso-C16 : 0. These data further strengthened placement of the strain within the genus Microbacterium . Strain SK 18T shared highest 16S rRNA gene sequence similarity (97.2 %) with Microbacterium ulmi DSM 16931T. Levels of similarity with the type strains of all other recognized Microbacterium species were less than 97.0 %. DNA–DNA hybridization experiments with strain SK 18T and its closest relative, M. ulmi DSM 16931T, revealed a low reassociation value of 39.0 % (σ = 3.8 %). Moreover, strain SK 18T showed a number of differences in phenotypic characteristics (colony colour, catalase activity, hydrolysis of polymers, acid production from sugars and oxidation of various substrates), and its DNA G+C content was also higher than that of M. ulmi DSM 16931T. These data indicated that strain SK 18T represents a novel species of the genus Microbacterium , for which the name Microbacterium immunditiarum sp. nov. is proposed. The type strain is SK 18T ( = MTCC 7185T = JCM 14034T). An emended description of the genus Microbacterium is also provided.

Microbacterium radiodurans sp. nov., a UV radiation-resistant bacterium isolated from soil

Strain GIMN 1.002(T), a UV radiation-tolerant bacterium, was isolated from the upper sand layers of the Gobi desert, Xinjiang, China and characterized in order to determine its taxonomic position. Cells were Gram-reaction-positive, heterotrophic, strictly aerobic, short rods. 16S rRNA gene sequence analysis revealed that strain GIMN 1.002(T) belonged to the genus Microbacterium and was closely related to Microbacterium arborescens DSM 20754(T) (98.8 % 16S rRNA gene sequence similarity) and Microbacterium imperiale DSM 20530(T) (98.7 %). However, strain GIMN 1.002(T) had low DNA-DNA relatedness with M. arborescens DSM 20754(T) (17.1 %) and M. imperiale DSM 20530(T) (12.89 %). Strain GIMN 1.002(T) possessed chemotaxonomic markers that were consistent with its classification in the genus Microbacterium, i.e. MK-11, MK-12 and MK-10 as major menaquinones and anteiso-C(15 : 0) (38.67 %), iso-C(16 : 0) (18.16 %) and iso-C(15 : 0) (17.46 %) as predominant cellular fatty acids. The DNA G+C content was 67.74 mol%. The cell-wall sugar was rhamnose. On the basis of the data from this study, strain GIMN 1.002(T) represents a novel species of the genus Microbacterium, for which the name Microbacterium radiodurans sp. nov. is proposed. The type strain is GIMN 1.002(T) (=CCTCC M208212(T) =NRRL B-24799(T)).

Microbacterium binotii sp. nov., isolated from human blood

Two strains of non-spore-forming, rod-shaped, Gram-positive bacteria, CIP 101303(T) and CIP 102116, were isolated from human blood in 1976 and 1977, respectively. These strains had chemotaxonomic markers that were consistent with classification in the genus Microbacterium, i.e. MK-10, MK-11 and MK-12 as the major menaquinones, predominant iso- and anteiso-branched cellular fatty acids, galactose, mannose and rhamnose as the cell-wall sugars and ornithine as the diamino acid in the cell-wall peptidoglycan. The DNA G+C content was 70-72 mol%. Comparative 16S rRNA gene sequence studies revealed that strains CIP 101303(T) and CIP 102116 belonged to the genus Microbacterium and that they were related closely to Microbacterium halotolerans. The level of DNA-DNA relatedness showed that the two isolates represented a separate genomic species. Based on phenotypic and genotypic results, it is proposed that strains CIP 101303(T) and CIP 102116 be assigned to a novel species, Microbacterium binotii sp. nov. The type strain is CIP 101303(T) (=DSM 19164(T)).

Identities of Microbacterium spp. encountered in human clinical specimens

In the present study, 50 strains of yellow-pigmented gram-positive rods that had been isolated from human clinical specimens and collected over a 5-year period were further characterized by phenotypic and molecular genetic methods. All 50 strains belonged to the genus Microbacterium, and together they represented 18 different species. Microbacterium oxydans (n = 11), M. paraoxydans (n = 9), and M. foliorum (n = 7) represented more than half of the strains included in the present study. The isolation of strains belonging to M. hydrocarbonoxydans (n = 2), M. esteraromaticum (n = 1), M. oleivorans (n = 1), M. phyllosphaerae (n = 1), and M. thalassium (n = 1) from humans is reported for the first time. Microbacterium sp. strain VKM Ac-1389 (n = 1) and the previously uncultured Microbacterium sp. clone YJQ-29 (n = 1) probably represent new species. Comprehensive antimicrobial susceptibility data are given for the 50 Microbacterium isolates. This study is, so far, the largest on Microbacterium spp. encountered in human clinical specimens and outlines the heterogeneity of clinical Microbacterium strains.

Manganese(II)-oxidizing Bacillus spores in Guaymas Basin hydrothermal sediments and plumes

Microbial oxidation and precipitation of manganese at deep-sea hydrothermal vents are important oceanic biogeochemical processes, yet nothing is known about the types of microorganisms or mechanisms involved. Here we report isolation of a number of diverse spore-forming Mn(II)-oxidizing Bacillus species from Guaymas Basin, a deep-sea hydrothermal vent environment in the Gulf of California, where rapid microbially mediated Mn(II) oxidation was previously observed. mnxG multicopper oxidase genes involved in Mn(II) oxidation were amplified from all Mn(II)-oxidizing Bacillus spores isolated, suggesting that a copper-mediated mechanism of Mn(II) oxidation could be important at deep-sea hydrothermal vents. Phylogenetic analysis of 16S rRNA and mnxG genes revealed that while many of the deep-sea Mn(II)-oxidizing Bacillus species are very closely related to previously recognized isolates from coastal sediments, other organisms represent novel strains and clusters. The growth and Mn(II) oxidation properties of these Bacillus species suggest that in hydrothermal sediments they are likely present as spores that are active in oxidizing Mn(II) as it emerges from the seafloor.

Interstitial pulmonary inflammation due to Microbacterium sp. after heart transplantation

A coryneform bacterium was isolated from the bronchoalveolar aspirate of a patient with interstitial pulmonary inflammation. Commercial systems identified the isolate as Corynebacterium sp. or Aureobacterium sp./Corynebacterium aquaticum, but 16S rRNA gene analysis unequivocally attributed it to the genus Microbacterium. This represents the first documented case of Microbacterium pulmonary infection.

Characterisation of the nitrile hydratase gene clusters of Rhodococcus erythropolis strains AJ270 and AJ300 and Microbacterium sp. AJ115 indicates horizontal gene transfer and reveals an insertion of IS1166

The nitrile metabolising strains AJ270, AJ300 and AJ115 were isolated from the same location. The strains have very similar nitrile metabolising profiles. Sequencing of the 16S rRNA gene indicates that strains AJ270 and AJ300 are novel strains of Rhodococcus erythropolis while strain AJ115 is a novel Microbacterium strain very closely related to Microbacterium oxydans and Microbacterium liquefaciens. Analysis of the structure of the nitrile hydratase/amidase gene clusters in the three strains indicates that this region is identical in these strains and that this structure is different to other nitrile hydratase/amidase gene clusters. The major difference seen is the insertion of a complete copy of the insertion sequence IS1166 in the nhr2 gene. This copy of IS1166 generates a 10 bp direct duplication at the point of insertion and has one ORF encoding a protein of 434 amino acids, with 98% homology to the transposase of IS666 from Mycobacterium avium. A gene oxd, encoding aldoxime dehydratase is found upstream of the nitrile hydratase gene cluster and an open reading frame encoding a protein with homology to GlnQ type ABC transporters is found downstream of the nitrile hydratase/amidase genes. The identity of the nitrile hydratase/amidase gene clusters in the three strains suggests horizontal gene transfer of this region. Analysis of the strains for both linear and circular plasmids indicates that both are present in the strains but hybridisation studies indicate that the nitrile hydratase/amidase gene cluster is chromosomally located. The nitrile hydratase/amidase enzymes of strain AJ270 are inducible with acetonitrile or acetamide. Interestingly although a number of Fe-type nitrile hydratases have been shown to be photosensitive, the enzyme from strain AJ270 is not.

Microbacterium oleivorans sp. nov. and Microbacterium hydrocarbonoxydans sp. nov., novel crude-oil-degrading Gram-positive bacteria

A taxonomic study of two crude-oil-degrading, Gram-positive bacterial strains, designated BAS69T and BNP48T, revealed that they represent two novel Microbacterium species. 16S rRNA gene sequence similarity to their closest phylogenetic neighbours was 98·5 % for BAS69T (Microbacterium paraoxydans DSM 15019T and Microbacterium saperdae DSM 20169T) and 99 % for BNP48T (Microbacterium luteolum DSM 20143T). Levels of DNA–DNA relatedness to the closest phylogenetic neighbours of both strains were between 11 and 38 %. According to phylogenetic analysis, the two strains are distinguishable from all recognized species of Microbacterium. Morphological and physiological characteristics of strains BAS69T and BNP48T were different from those of phylogenetically closely related Microbacterium species. The diamino acid in the cell-wall peptidoglycan of BAS69T is lysine and of BNP48T is ornithine. The major menaquinones are MK-11 and MK-12 for both strains. Based on their ability to degrade crude oil, the name Microbacterium oleivorans sp. nov. is proposed for strain BAS69T (=DSM 16091T=NCIMB 14003T) and Microbacterium hydrocarbonoxydans is proposed for strain BNP48T (=DSM 16089T=NCIMB 14002T).

Bacteria associated with cysts of the soybean cyst nematode (Heterodera glycines)

The soybean cyst nematode (SCN), Heterodera glycines, causes economically significant damage to soybeans (Glycine max) in many parts of the world. The cysts of this nematode can remain quiescent in soils for many years as a reservoir of infection for future crops. To investigate bacterial communities associated with SCN cysts, cysts were obtained from eight SCN-infested farms in southern Ontario, Canada, and analyzed by culture-dependent and -independent means. Confocal laser scanning microscopy observations of cyst contents revealed a microbial flora located on the cyst exterior, within a polymer plug region and within the cyst. Microscopic counts using 5-(4,6-dichlorotriazine-2-yl)aminofluorescein staining and in situ hybridization (EUB 338) indicated that the cysts contained (2.6 +/- 0.5) x 10(5) bacteria (mean +/- standard deviation) with various cellular morphologies. Filamentous fungi were also observed. Live-dead staining indicated that the majority of cyst bacteria were viable. The probe Nile red also bound to the interior polymer, indicating that it is lipid rich in nature. Bacterial community profiles determined by denaturing gradient gel electrophoresis analysis were simple in composition. Bands shared by all eight samples included the actinobacterium genera Actinomadura and STREPTOMYCES: A collection of 290 bacteria were obtained by plating macerated surface-sterilized cysts onto nutrient broth yeast extract agar or on actinomycete medium. These were clustered into groups of siblings by repetitive extragenic palindromic PCR fingerprinting, and representative isolates were tentatively identified on the basis of 16S rRNA gene sequence. Thirty phylotypes were detected, with the collection dominated by Lysobacter and Variovorax spp. This study has revealed the cysts of this important plant pathogen to be rich in a variety of bacteria, some of which could presumably play a role in the ecology of SCN or have potential as biocontrol agents.

Isolation and characterization of efficient isoxaben-transforming Microbacterium sp strains from four European soils

Nutrient-agar plates containing isoxaben (500 mg litre(-1)) were used to isolate isoxaben-metabolising bacteria from four European soils incubated with the herbicide under laboratory conditions. In flask experiments, inoculation of a basal salts medium containing nitrogen and [phenyl-U-14C]isoxaben with an isolate (B2b) resulted in 33% recovery of the initial radioactivity as [14C]carbon dioxide after 2 weeks. A major metabolite identified by GC-MS and NMR analysis as 3-(1-ethyl-1-methylpropyl)isoxazol-5-ylamine accumulated both in basal salts and nutrient broth media. 2,6-Dimethoxybenzoic acid, a suspected metabolite of isoxaben, was not detected in either liquid media. However, the capability of the B2b isolate to use 2,6-dimethoxybenzoic acid as a source of carbon was demonstrated. Soil inoculation with the B2b strain resulted in an increase in the recovery of [14C] carbon dioxide from both [phenyl-U-14C] and [isoxazole-5-14C]isoxaben. The metabolite identified as 3-(1-ethyl-1-methylpropyl)isoxazole-5-ylamine only accumulated if the soil was autoclaved before inoculation. This metabolite was rapidly mineralized by the microflora of a natural soil without history of isoxaben treatment. Homology patterns of sequenced 16S rDNA between isoxaben-transforming isolates and reference strains showed that the four isolates identified belonged to the genus Microbacterium.

Isolation and characterization of endophytic colonizing bacteria from agronomic crops and prairie plants

Endophytic bacteria reside within plant hosts without causing disease symptoms. In this study, 853 endophytic strains were isolated from aerial tissues of four agronomic crop species and 27 prairie plant species. We determined several phenotypic properties and found approximately equal numbers of gram-negative and gram-positive isolates. In a greenhouse study, 28 of 86 prairie plant endophytes were found to colonize their original hosts at 42 days postinoculation at levels of 3.5 to 7.7 log(10) CFU/g (fresh weight). More comprehensive colonization studies were conducted with 373 corn and sorghum endophytes. In growth room studies, none of the isolates displayed pathogenicity, and 69 of the strains were recovered from corn or sorghum seedlings at levels of 8.3 log(10) CFU/plant or higher. Host range greenhouse studies demonstrated that 26 of 29 endophytes were recoverable from at least one host other than corn and sorghum at levels of up to 5.8 log(10) CFU/g (fresh weight). Long-range dent corn greenhouse studies and field trials with 17 wild-type strains and 14 antibiotic-resistant mutants demonstrated bacterial persistence at significant average colonization levels ranging between 3.4 and 6.1 log(10) CFU/g (fresh weight) up to 78 days postinoculation. Three prairie and three agronomic endophytes exhibiting the most promising levels of colonization and an ability to persist were identified as Cellulomonas, Clavibacter, Curtobacterium, and Microbacterium isolates by 16S rRNA gene sequence, fatty acid, and carbon source utilization analyses. This study defines for the first time the endophytic nature of Microbacterium testaceum. These microorganisms may be useful for biocontrol and other applications.