Co-exposure to environmental microplastic and the pesticide 2,4-dichlorophenoxyacetic acid (2,4-D) induce distinctive alterations in the metabolome and microbial community structure in the gut of the earthworm Eisenia andrei

Microplastics (MPs) are recognized as emergent pollutants and have become a significant environmental concern, especially when combined with other contaminants. In this study, earthworms, specifically Eisenia andrei, were exposed to MPs (at a concentration of 10 μg kg-1 of soil), herbicide 2,4-D (7 mg kg-1 of soil), and a combination of the two for 7 and 14 days. The chemical uptake in the earthworms was measured, and the bacterial and archaeal diversities in both the soil and earthworm gut were analyzed, along with the metabolomic profiles. Additionally, data integration of the two omics approaches was performed to correlate changes in gut microbial diversity and the different metabolites. Our results demonstrated that earthworms ingested MPs and increased 2,4-D accumulation. More importantly, high-throughput sequencing revealed a shift in microbial diversity depending on single or mixture exposition. Metabolomic data demonstrated an important modulation of the metabolites related to oxidative stress, inflammatory system, amino acids synthesis, energy, and nucleic acids metabolism, being more affected in case of co-exposure. Our investigation revealed the potential risks of MPs and 2,4-D herbicide combined exposure to earthworms and soil fertility, thus broadening our understanding of MPs' toxicity and impacts on terrestrial environments.

Leucobacter edaphi sp. nov., a highly chromate-tolerant bacterium isolated from chromium containing chemical plant soil

A Gram-positive, aerobic, rod-shaped non-motile, non-sporulating bacterium, designated CSA2T, was isolated from chromium-containing soils collected from a chemical plant. The 16S rRNA gene sequence of strain CSA2T showed the highest homology with Leucobacter chromiireducens subsp. solipictus (97.85%), Leucobacter chromiireducens subsp. chromiireducens (97.85%). The digital DNA-DNA hybridization (dDDH), average nucleotide identity (ANI) and the amino acid identity (AAI) values among strains CSA2T and the selected Leucobacter species were 20.6-23.4% (dDDH), 72.67-78.03% (ANI) and 66.39-76.16% (AAI), falling below the recommended thresholds for species delimitation. The principal fatty acids were anteiso-C15:0, iso-C16:0 and anteiso-C17:0. The polar lipids were phosphatidylglycerol, diphosphatidylglycerol and an unknown glycolipid. The major menaquinones detected were MK-10 and MK-11. The cell-wall amino acids included 2,4-diaminobutyric acid, threonine, glutamic acid, alanine and glycine. Based on molecular feature, phenotypic and chemotaxonomic, strain CSA2T was considered to be a novel species of the genus Leucobacter., and the name Leucobacter edaphi sp. nov. is proposed. The type strain is CSA2T (= JCM 34360T = CGMCC 1.18747T).

Leucobacter chinensis sp. nov., with plant growth-promoting potential isolated from field soil after seven-years continuous maize cropping

A novel Gram-stain-positive, aerobic, non-motile and rod-shaped bacterium, designated strain NC76-1^T, was isolated from soil from a field that had undergone seven years continuous maize cropping from Liuba town located in Zhangye city, Gansu province, PR China. Colonies of strain NC76-1^T were white, opaque and circular with a convex shape. The isolate was found to be able to grow at 10-40 °C (optimum 30 °C), pH 6.0 to 12.0 (optimum 7.0-8.0) and with 0-5.0 % (w/v) NaCl (optimum 0%). On the basis of the results of 16S rRNA gene sequence analysis, the strain fell within the clade of the genus Leucobacter, showing the highest sequence similarities with Leucobacter iarius 40^T (97.4%), Leucobacter aridicollis CIP 108388^T (97.0%), Leucobacter chromiireducens subsp. solipictus TAN 31504^T (96.7%) and Leucobacter denitrificans M1T8B10^T (96.7%). The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between NC76-1^T and its closest relatives, L. iarius 40^T, L. aridicollis CIP 108388^T, L. chromiireducens subsp. solipictus TAN 31504^T and L. denitrificans M1T8B10^T were ≤73.5 % and 20.3%, respectively. The genomic DNA G+C content of NC76-1^T was 61.5 mol%. It presented MK-11 as the predominant menaquinone. The major cellular fatty acids were anteiso-C_15 : 0 (49.2 %) and iso-C_16 : 0 (35.7%). The major polar lipids were found to be diphosphatidyglycerol, phosphatidylglycerol, phosphatidylethanolamine, aminoglycolipid, five glycolipid and one unidentified lipids. The cell wall amino acids were 2,4-diaminobutyric acid, alanine, glutamic acid, glycine and threonine. On the basis of the phylogenetic, phenotypic and chemotaxonomic characteristics, strain NC76-1^T is concluded to represent a novel species within the genus Leucobacter, for which the name Leucobacter chinensis sp. nov. is proposed. The type strain is NC76-1^T (GDMCC 1.2286^T= JCM 34651^T).

Bacterial but Not Fungal Rhizosphere Community Composition Differ among Perennial Grass Ecotypes under Abiotic Environmental Stress

Environmental change, especially frequent droughts, is predicted to detrimentally impact the North American perennial grasslands. Consistent dry spells will affect plant communities as well as their associated rhizobiomes, possibly altering the plant host performance under environmental stress. Therefore, there is a need to understand the impact of drought on the rhizobiome, and how the rhizobiome may modulate host performance and ameliorate its response to drought stress. In this study, we analyzed bacterial and fungal communities in the rhizospheres of three ecotypes (dry, mesic, and wet) of dominant prairie grass, Andropogon gerardii. The ecotypes were established in 2010 in a common garden design and grown for a decade under persistent dry conditions at the arid margin of the species' range in Colby, Kansas. The experiment aimed to answer whether and to what extent do the different ecotypes maintain or recruit distinct rhizobiomes after 10 years in an arid climate. In order to answer this question, we screened the bacterial and fungal rhizobiome profiles of the ecotypes under the arid conditions of western Kansas as a surrogate for future climate environmental stress using 16S rRNA and ITS2 metabarcoding sequencing. Under these conditions, bacterial communities differed compositionally among the A. gerardii ecotypes, whereas the fungal communities did not. The ecotypes were instrumental in driving the differences among bacterial rhizobiomes, as the ecotypes maintained distinct bacterial rhizobiomes even after 10 years at the edge of the host species range. This study will aid us to optimize plant productivity through the use of different ecotypes under future abiotic environmental stress, especially drought. IMPORTANCE In this study, we used a 10-year long reciprocal garden system, and reports that different ecotypes (dry, mesic, and wet) of dominant prairie grass, Andropogon gerardii can maintain or recruit distinct bacterial but not fungal rhizobiomes after 10 years in an arid environment. We used both 16S rRNA and ITS2 amplicons to analyze the bacterial and fungal communities in the rhizospheres of the respective ecotypes. We showed that A. gerardii might regulate the bacterial community to adapt to the arid environment, in which some ecotypes were not adapted to. Our study also suggested a possible tradeoff between the generalist and the specialist bacterial communities in specific environments, which could benefit the plant host. Our study will provide insights into the plant host regulation of the rhizosphere bacterial and fungal communities, especially during frequent drought conditions anticipated in the future.

Leucobacter chromiisoli sp. nov., isolated from chromium-containing chemical plant soil

A Gram-stain-positive, rod-shaped, aerobic, non-motile, non-sporulating bacterial strain, designated CSA1^T, was isolated from chromium-containing soil sampled at a chemical plant. Growth of strain CSA1^T occurred at pH 6-10 (optimum, pH 7), 15-45 °C (optimum, 30 °C) and in the presence of 0.5-6.5 % (w/v) NaCl (optimum, 2 %). The 16S rRNA gene sequence of strain CSA1^T revealed the highest similarity to Leucobacter ruminantium A2^T (97.5 %), Leucobacter tardus K 70/01^T (97.3 %), Leucobacter humi Re6^T (96.6 %), Leucobacter kyeonggiensis F3-P9^T (96.2 %), Leucobacter zeae CC-MF41^T (96.1 %) and Leucobacter weissii S27^T (96.0 %). The draft genome of CSA1^T was approximately 3 350 931 bp in size with a G+C content of 70.6 mol%. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values among strain CSA1^T and the selected Leucobacter species were 74.0-79.2 % (ANIb), 84.3-87.1 % (ANIm) and 21.5-25.4 % (dDDH), which are below the recommended cutoff values for species delineation. The major fatty acids were anteiso-C_15 : 0, iso-C_16 : 0 and anteiso-C_17 : 0. The polar lipids were diphosphatidylglycerol, phosphatidylglycerol and an unknown glycolipid. The predominant menaquinones were MK-11, MK-8 and MK-6. The cell-wall amino acids were 2,4-diaminobutyric acid, alanine, glycine, glutamic acid and threonine. From the phenotypic, chemotaxonomic and molecular features, strain CSA1^T was considered to represent a novel species of the genus Leucobacter, for which the name Leucobacter chromiisoli sp. nov. is proposed. The type strain is CSA1^T (=JCM 34359^T=CGMCC 1.18746^T).

Chromate Resistance Mechanisms in Leucobacter chromiiresistens

Chromate is one of the major anthropogenic contaminants on Earth. Leucobacter chromiiresistens is a highly chromate-resistant strain, tolerating chromate concentrations in LB medium of up to 400 mM. In response to chromate stress, L. chromiiresistens forms biofilms, which are held together via extracellular DNA. Inhibition of biofilm formation leads to drastically decreased chromate tolerance. Moreover, chromate is reduced intracellularly to the less-toxic Cr(III). The oxidation status and localization of chromium in cell aggregates were analyzed by energy-dispersive X-ray spectroscopy coupled to scanning transmission electron microscopy and X-ray absorption spectroscopy measurements. Most of the heavy metal is localized as Cr(III) at the cytoplasmic membrane. As a new cellular response to chromate stress, we observed an increased production of the carotenoid lutein. Carotenoid production could increase membrane stability and reduce the concentration of reactive oxygen species. Bioinformatic analysis of the L. chromiiresistens genome revealed several gene clusters that could enable heavy-metal resistance. The extreme chromate tolerance and the unique set of resistance factors suggest the use of L. chromiiresistens as a new model organism to study microbial chromate resistance.IMPORTANCE Chromate is a highly toxic oxyanion. Extensive industrial use and inadequate waste management has caused the toxic pollution of several field sites. Understanding the chromate resistance mechanisms that enable organisms to thrive under these conditions is fundamental to develop (micro)biological strategies and applications aiming at bioremediation of contaminated soils or waters. Potential detoxifying microorganisms are often not sufficient in their resistance characteristics to effectively perform, e.g., chromate reduction or biosorption. In this study, we describe the manifold strategies of L. chromiiresistens to establish an extremely high level of chromate resistance. The multitude of mechanisms conferring it make this organism suitable for consideration as a new model organism to study chromate resistance.

Characteristics of microbial community involved in early biofilms formation under the influence of wastewater treatment plant effluent

Effluents from wastewater treatment plants (WWTPs) containing microorganisms and residual nutrients can influence the biofilm formation. Although the process and mechanism of bacterial biofilm formation have been well characterized, little is known about the characteristics and interaction of bacteria, archaea and eukaryotes in the early colonization, especially under the influence of WWTP effluent. The aim of this study was to characterize the important bacterial, archaeal and eukaryotic species in the early stage of biofilm formation downstream of the WWTP outlet. Water and biofilm samples were collected 24 and 48hr after the deposition of bio-cords in the stream. Illumina Miseq sequencing of the 16S and 18S rDNA showed that, among the three domains, the bacterial biofilm community had the largest alpha and beta diversity. The early bacterial colonizers appeared to be "biofilm-specific", with only a few dominant operational taxonomic units (OTUs) shared between the biofilm and the ambient water environment. Alpha-proteobacteria and Ciliophora tended to dominate the bacterial and eukaryotic communities, respectively, of the early biofilm already at 24hr, whereas archaea played only a minor role during the early stage of colonization. The network analysis showed that the three domains of microbial community connected highly during the early colonization and it might be a characteristic of the microbial communities in the biofilm formation process where co-occurrence relationships could drive coexistence and diversity maintenance within the microbial communities.

Leucobacter weissii sp. nov., an isolate from activated sludge once described as first representative of the peptidoglycan variation B2δ, and emended description of the genus Leucobacter

Strain S27^T is a Gram-stain-positive, regular rod-shaped, non-motile, non-spore-forming, yellow pigmented actinobacterium which was isolated from an aerated laboratory scale fermenter fed with wastes of a yeast factory. The strain was classified as Microbacterium sp. after the analysis of its peptidoglycan revealed a novel B-type structure established as variation B2δ by Hensel in 1984. As the combination of the peptidoglycan amino acids 2,4-diaminobutyric acid (Dab), threonine (Thr), glycine (Gly), alanine (Ala) and glutamic acid (Glu) is in disagreement with the current genus definition of Microbacterium but is typical of several Leucobacter species, the taxonomic status of strain S27^T was re-examined by a polyphasic study. Comparative analyses of 16S rRNA gene sequences and the occurrence of l-Dab, d-Ala, l-Ala, Gly, l-Thr, d-Glu and lower amounts of l-Glu in the peptidoglycan in combination with the predominating menaquinones MK-11, MK-10 and MK-9, phosphatidylglycerol, and one unknown glycolipid as the major polar lipids (and trace amounts of diphosphatidylglycerol and an unknown phospholipid), a profile with anteiso-C15 : 0, iso-C15 : 0, iso-C16 : 0, anteiso-C17 : 0 and iso-C17 : 0 as major fatty acids and the G+C value of 70.1 mol% confirmed the affiliation to the genus Leucobacter and revealed that S27^T (=DSM 20621^T =CCM 8762^T) is the type strain of a new species for which the name Leucobacter weissii sp. nov. is proposed. The availability of new data allows for an emended description of the genus Leucobacter.

High-Quality Draft Genome Sequence of Leucobacter sp. Strain G161, a Distinct and Effective Chromium Reducer

Here, we report the genome sequence for Leucobacter sp. strain G161 due to its distinct and effective hexavalent chromium reduction under aerobic growth conditions, followed by facultative anaerobic incubation. The draft genome sequence of Leucobacter sp. G161 comprises 3,554,188 bp, with an average G+C content of 65.3%, exhibiting 3,341 protein-coding genes and 55 predicted RNA genes.

Leucobacter zeae sp. nov., isolated from the rhizosphere of maize (Zea mays L.)

A novel yellow-pigmented, aerobic, rod-shaped, non-motile bacterium, designated strain CC-MF41T, was isolated from rhizosphere soil of maize (Zea mays) collected in Wufeng District, Taichung, Taiwan. Strain CC-MF41T exhibited 16S rRNA gene sequence similarity of 97.5, 97.3, 97.2 and 97.1 % to Leucobacter chironomi MM2LBT (and ‘Leucobacter kyeonggiensis’ F3-P9 and ‘L. humi’ Re-6, the names of which have not been validly published), Leucobacter tardus K70/01T, L. komagatae IFO 15245T and ‘Leucobacter margaritiformis’ A23. However, CC-MF41T and ‘L. margaritiformis’ A23 formed a loosely bound phylogenetic lineage (with a low bootstrap value) associated with species of the genus Leucobacter. In DNA–DNA reassociation experiments, the relatedness of strain CC-MF41T to L. chironomi DSM 19883T was 57.1 % (reciprocal value 29.1 %). The DNA G+C content of strain CC-MF41T was 72.1 mol% and the cell-wall peptidoglycan contained 2,4-diaminobutyric acid, alanine, glycine, glutamic acid and threonine. The major menaquinone was MK-11 and the predominant fatty acids were iso-C16 : 0, anteiso-C15 : 0 and anteiso-C17 : 0. The polar lipid profile of strain CC-MF41T contained major amounts of diphosphatidylglycerol followed by an unidentified glycolipid, phosphatidylglycerol and an unknown phospholipid. Based on its phylogenetic, phenotypic and chemotaxonomic distinctiveness, strain CC-MF41T represents a novel species of Leucobacter, for which the name Leucobacter zeae sp. nov. is proposed. The type strain is CC-MF41T ( = BCRC 80515T = LMG 27265T).

Leucobacter musarum subsp. musarum sp. nov., subsp. nov., Leucobacter musarum subsp. japonicus subsp. nov., and Leucobacter celer subsp. astrifaciens subsp. nov., three nematopathogenic bacteria isolated from Caenorhabditis, with an emended description of Leucobacter celer

Three Gram-stain-positive, irregular-rod-shaped, non-motile, non-spore-forming bacteria were isolated from nematodes collected from Santa Antao, Cabo Verde (CBX151^T, CBX152^T) and Kakegawa, Japan (CBX130^T). Based on 16S rRNA gene sequence similarity, strains CBX130^T, CBX151^T and CBX152^T were shown to belong to the genus Leucobacter. This affiliation was supported by chemotaxonomic data (2,4-diaminobutyric acid in the cell wall; major respiratory quinones MK-10 and MK-11; major polar lipids phosphatidylglycerol and diphosphatidylglycerol; major fatty acids anteiso-C_15 : 0, anteiso-C_17 : 0 and iso-C_16 : 0). Strains CBX130^T and CBX152^T were found to share salient characteristics. Based on morphological, physiological, chemotaxonomic and biochemical analysis, strain CBX152^T represents a novel species of the genus Leucobacter, for which the name Leucobacter musarum sp. nov. (type strain CBX152^T = DSM 27160^T = CIP 110721^T) is proposed. Two subspecies of Leucobacter musarum sp. nov. are proposed: Leucobacter musarum sp. nov. subsp. musarum subsp. nov. (type strain CBX152^T = DSM 27160^T = CIP 110721^T) and Leucobacter musarum sp. nov. subsp. japonicus subsp. nov. (type strain CBX130^T = DSM 27158^T = CIP 110719^T). The third novel strain, CBX151^T, showed genetic similarities with Leucobacter celer NAL101^T indicating that these strains belong to the same species. Based on morphological, physiological, chemotaxonomic and biochemical differences it is proposed to split the species Leucobacter celer into two novel subspecies, Leucobacter celer subsp. celer subsp. nov. (type strain NAL101^T = KACC 14220^T = JCM 16465^T) and Leucobacter celer subsp. astrifaciens subsp. nov. (type strain CBX151^T = DSM 27159^T = CIP 110720^T), and to emend the description of Leucobacter celerShin et al. 2011.

High quality draft genome sequence of Leucobacter chironomi strain MM2LB(T) (DSM 19883(T)) isolated from a Chironomus sp. egg mass

Leucobacter chironomi strain MM2LB^T (Halpern et al., Int J Syst Evol Microbiol 59:665-70 2009) is a Gram-positive, rod shaped, non-motile, aerobic, chemoorganotroph bacterium. L. chironomi belongs to the family Microbacteriaceae, a family within the class Actinobacteria. Strain MM2LB^T was isolated from a chironomid (Diptera; Chironomidae) egg mass that was sampled from a waste stabilization pond in northern Israel. In a phylogenetic tree based on 16S rRNA gene sequences, strain MM2LB^T formed a distinct branch within the radiation encompassing the genus Leucobacter. Here we describe the features of this organism, together with the complete genome sequence and annotation. The DNA GC content is 69.90%. The chromosome length is 2,964,712 bp. It encodes 2,690 proteins and 61 RNA genes. L. chironomi genome is part of the Genomic Encyclopedia of Type Strains, Phase I: the one thousand microbial genomes (KMG) project.

Genome sequence of the chromate-resistant bacterium Leucobacter salsicius type strain M1-8(T.)

Leucobacter salsicius M1-8(T) is a member of the Microbacteriaceae family within the class Actinomycetales. This strain is a Gram-positive, rod-shaped bacterium and was previously isolated from a Korean fermented food. Most members of the genus Leucobacter are chromate-resistant and this feature could be exploited in biotechnological applications. However, the genus Leucobacter is poorly characterized at the genome level, despite its potential importance. Thus, the present study determined the features of Leucobacter salsicius M1-8(T), as well as its genome sequence and annotation. The genome comprised 3,185,418 bp with a G+C content of 64.5%, which included 2,865 protein-coding genes and 68 RNA genes. This strain possessed two predicted genes associated with chromate resistance, which might facilitate its growth in heavy metal-rich environments.

Draft genome sequence of Leucobacter chromiiresistens, an extremely chromium-tolerant strain

Here we present the draft genome of Leucobacter chromiiresistens. This is the first genome sequence of an organism belonging to the genus Leucobacter. L. chromiiresistens was sequenced due to its capability to tolerate up to 300 mM Cr(VI) in the medium, which is so far a unique feature for microorganisms.

Leucobacter celer sp. nov., isolated from Korean fermented seafood

A novel, Gram-reaction-positive, aerobic, rod-shaped, non-motile bacterial strain, designated NAL101T, was isolated from gajami-sikhae, a traditional Korean fermented seafood made of flatfish. Growth occurred at 4–45 °C, at pH 5–10 and in 0–12 % (w/v) NaCl. Optimum growth occurred at 30–37 °C, at pH 8 and in 0–1 % (w/v) NaCl. The cell-wall amino acids were 2,4-diaminobutyric acid, alanine, glycine, threonine and glutamic acid and the major fatty acids were anteiso-C15 : 0, iso-C16 : 0 and anteiso-C17 : 0. The predominant menaquinone was MK-11. The major polar lipids were diphosphatidylglycerol, phosphatidylglycerol and an unknown glycolipid. The 16S rRNA gene sequence of strain NAL101T showed 97.7 % similarity to that of Leucobacter chironomi MM2LBT, its closest relative. The DNA G+C content was 68.8 mol% and DNA–DNA hybridization values with closely related strains were <22 %. Phylogenetic analyses based on 16S rRNA gene sequences as well as differences in its physiological and biochemical characteristics indicated that strain NAL101T represents a novel species of the genus Leucobacter in the family Microbacteriaceae, for which the name Leucobacter celer sp. nov. is proposed. The type strain is NAL101T ( = KACC 14220T  = JCM 16465T).

Leucobacter chromiiresistens sp. nov., a chromate-resistant strain

A Gram-positive, irregular rod-shaped, non-motile, yellow-pigmented bacterium, strain JG 31T, was isolated in the course of identifying chromium-resistant soil bacteria. 16S rRNA gene sequence analysis of the isolated bacterium indicated its phylogenetic position within the genus Leucobacter. Binary 16S rRNA gene sequence alignments of the isolated bacterium with the 11 species of the genus recognized at the time of writing revealed sequence similarities of more than 97 % with Leucobacter alluvii (GenBank accession no: AM072820; 99.4 %), Leucobacter iarius (AM040493; 98.2 %), Leucobacter aridicollis (AJ781047; 97.8 %), Leucobacter komagatae (AB007419; 97.4 %), Leucobacter chironomi (EU346911; 97.1 %) and Leucobacter luti (AM072819; 97.1 %). In contrast, DNA–DNA hybridization experiments showed similarity values below 28 % for DNA samples from the most closely related type strains of L. alluvii, L. aridicollis and L. iarius. Protein analysis by matrix-assisted laser-desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and automated RiboPrinting using the restriction enzyme PvuII differentiated strain JG 31T from all type strains of the genus Leucobacter. The dominant fatty acids of the novel isolate were anteiso-C15 : 0, anteiso-C17 : 0 and iso-C16 : 0, while the quinone system consisted of menaquinones MK-11, MK-10, MK-9 and MK-8. In a B-type cross-linked peptidoglycan, the cell-wall amino acids were alanine, glycine, threonine, glutamic acid and 2,4-diaminobutyric acid. Strain JG 31T was able to grow in a medium containing up to 300 mM K2CrO4 and showed cellular aggregation in response to chromate stress. From biochemical and genomic analyses, the new strain is considered to represent a novel species of the genus Leucobacter, for which the name Leucobacter chromiiresistens sp. nov. is proposed. The type strain is strain JG 31T ( = DSM 22788T  = CCOS 200T).

Leucobacter salsicius sp. nov., from a salt-fermented food

Strain M1-8T was isolated from jeotgal, a Korean salt-fermented food. Cells were aerobic, non-motile, Gram-reaction-positive and rod-shaped. Colonies were cream-coloured and circular with entire margins. Strain M1-8T exhibited optimal growth at 25–30 °C and pH 7.0–8.0 and in 0–4 % (w/v) NaCl. The strain tolerated up to 10.0 mM Cr(VI). Phylogenetic analyses of 16S rRNA gene sequences indicated that strain M1-8T represents a novel species in the genus Leucobacter. The 16S rRNA gene sequence of M1-8T exhibited 98.1 % similarity to that of Leucobacter chromiireducens subsp. chromiireducens L-1T. The new isolate was clustered with Leucobacter species on a 16S rRNA gene sequence-based phylogenetic tree. The chromosomal DNA G+C content of strain M1-8T was 62.8 mol%. Its cell-wall peptidoglycan contained 2,4-diaminobutyric acid, glutamic acid, alanine, glycine and γ-aminobutyric acid. The major menaquinone was MK-11 and the predominant fatty acids were anteiso-C15 : 0 (63.6 %), anteiso-C17 : 0 (16.7 %) and iso-C16 : 0 (14.2 %). The polar lipid profile of strain M1-8T contained diphosphatidylglycerol and one unknown glycolipid. Significant genotypic and phenotypic differences were found between strain M1-8T and other Leucobacter species. These differentiating characteristics indicate that strain M1-8T represents a novel species of the genus Leucobacter, for which the name Leucobacter salsicius sp. nov. is proposed. The type strain is M1-8T (=KACC 21127T =JCM 16362T).

Leucobacter aerolatus sp. nov., from the air of a duck barn

A Gram-positive, non-spore-forming actinobacterium (Sj 10T) was isolated on tryptone soy agar from the air of a duck barn after filter sampling. Based on 16S rRNA gene sequence similarity studies, strain Sj 10T was shown to belong to the genus Leucobacter and was closely related to Leucobacter chromiireducens subsp. chromiireducens L-1T (97.8 %), Leucobacter tardus DSM 19811T (97.3 %) and Leucobacter luti RF6T (97.3 %). The peptidoglycan of strain Sj 10T contained 2,4-diaminobutyric acid in combination with a lower amount of lysine as diagnostic diamino acids. In addition, threonine, glycine, alanine and glutamic acid were found. Menaquinone MK-11 was the major respiratory quinone; MK-12 and MK-10 were detected in minor amounts. The polar lipid pattern consisted of phosphatidylglycerol, diphosphatidylglycerol and one unknown component each of a phospholipid, glycolipid and aminoglycolipid. Strain Sj 10T contained the major fatty acids anteiso-C15 : 0, iso-C16 : 0 and anteiso-C17 : 0, like other members of the genus Leucobacter. Results of DNA–DNA hybridization, physiological and biochemical tests enabled strain Sj 10T to be differentiated genotypically and phenotypically from the most closely related Leucobacter species. Strain Sj 10T represents a novel species of the genus Leucobacter, for which the name Leucobacter aerolatus sp. nov. is proposed, with Sj 10T (=DSM 22806T =CCM 7705T) as the type strain.

Virulence of Leucobacter chromiireducens subsp. solipictus to Caenorhabditis elegans: characterization of a novel host-pathogen interaction

We describe the pathogenic interaction between a newly described gram-positive bacterium, Leucobacter chromiireducens subsp. solipictus strain TAN 31504, and the nematode Caenorhabditis elegans. TAN 31504 pathogenesis on C. elegans is exerted primarily through infection of the adult nematode uterus. TAN 31504 enters the uterus through the external vulval opening, and the ensuing uterine infection is strongly correlated with a significant reduction in host life span. Young worms can feed and develop on TAN 31504, but not preferably over the standard food source. C. elegans worms reared on TAN 31504 as the sole food source develop into thin adults with little intestinal fat stores, produce few progeny, and subsequently cannot persist on the pathogenic food source. Within 12 h of exposure, adult worms challenged with TAN 31504 alter the expression of a number of C. elegans innate immunity-related genes, including nlp-29, which encodes a neuropeptide-like protein. C. elegans worms exposed briefly to TAN 31504 develop lethal uterine infections analogous to worms exposed continuously to pathogen, suggesting that mere contact with the pathogen is sufficient for the host to become infected. TAN 31504 produces a robust biofilm, and this behavior is speculated to play a role in the virulence exerted on the nematode host. The interaction between TAN 31504 and C. elegans provides a convenient opportunity to study bacterial virulence on nematode tissues other than the intestine and may allow for the discovery of host innate immunity elicited specifically in response to vulva-uterus infection.