Luteibacter pinisoli sp. nov., a casein degrading bacterium isolated from rhizospheric soil of Pinus koraiensis

Evaluation the role of Luteibacter pinisoli DP2-30 in mitigating pine wilt disease caused by Bursaphelenchus xylophilus through modulation of host microbiome

Background and aim

Pine wilt disease (PWD), caused by the pine wood nematode (PWN) Bursaphelenchus xylophilus, poses a significant threat to pine forests worldwide. This study aimed to isolate bacterial strains from the rhizosphere of healthy Pinus massoniana and elucidate their biocontrol potential in mitigating PWD through direct nematicidal activity and manipulation of host microbiome.

Results

We successfully isolated the rhizobacterium strain DP2-30 from rhizosphere of healthy pine plants, which was identified as Luteibacter pinisoli on the basis of morphological, biochemical, and molecular analyses. The fermentation filtrates of strain DP2-30 displayed direct nematicidal activity of >95% (corrected mortality rate) on PWN after 48 hours of treatment. The fermentation broth and filtrates of strain DP2-30 significantly inhibited PWN egg hatching by 49.38% and 43.05%, respectively. Additionally, root drenching of strain DP2-30 fermentation broth significantly reduced PWD severity in pine seedlings (2 years old), with a control effect of 62.50%. Microbiome analyses revealed significant variations in the diversity, structure, and relative abundance of bacterial and fungal communities of pine plants combined treated with DP2-30 and PWN (T2), solely treated with PWN (T1), and control (treated with water). Bacterial phyla, Proteobacteria, Actinobacteriota, Chloroflexi, Acidobacteriota, and Armatimonadota and fungal phyla Ascomycota, Basidiomycota and Mortierellomycota were dominant in the all root and stem samples. The application of L. pinisoli DP2-30 significantly increased the relative abundance of the family Rhodanobacteraceae in the roots and stems of pine seedlings. Additionally, intra-kingdom co-occurrence network analysis revealed reduced complexity in the bacterial networks but increased complexity in the fungal networks of treated plants, suggesting enhanced functional redundancy and ecosystem stability.

Conclusions

Overall, this study highlights the potential of L. pinisoli DP2-30 as an effective biocontrol agent against PWD by directly killing PWN and manipulating the host microbiota.

Luteibacter mycovicinus sp. nov., a yellow-pigmented gammaproteobacterium found as an endohyphal symbiont of endophytic Ascomycota

We isolated and described a yellow-pigmented strain of bacteria (strain 9143T), originally characterized as an endohyphal inhabitant of an endophytic fungus in the Ascomycota. Although the full-length sequence of its 16S rRNA gene displays 99 % similarity to Luteibacter pinisoli, genomic hybridization demonstrated <30 % genomic similarity between 9143T and its closest named relatives, further supported by average nucleotide identity results. This and related endohyphal strains form a well-supported clade separate from L. pinisoli and other validly named species including the most closely related Luteibacter rhizovicinus. The name Luteibacter mycovicinus sp. nov. is proposed, with type strain 9143T (isolate DBL433), for which a genome has been sequenced and is publicly available from the American Type Culture Collection (ATCC TSD-257T) and from the Leibniz Institute DSMZ (DSM 112764T). The type strain reliably forms yellow colonies across diverse media and growth conditions (lysogeny broth agar, King's Medium B, potato dextrose agar, trypticase soy agar and Reasoner's 2A (R2A) agar). It forms colonies readily at 27 °C on agar with a pH of 6-8, and on salt (NaCl) concentrations up to 2 %. It lacks the ability to utilize sulphate as a sulphur source and thus only forms colonies on minimal media if supplemented with alternative sulphur sources. It is catalase-positive and oxidase-negative. Although it exhibits a single polar flagellum, motility was only clearly visible on R2A agar. Its host range and close relatives, which share the endohyphal lifestyle, are discussed.

Coupling multifactor dominated the biochemical response and the alterations of intestinal microflora of earthworm Pheretima guillelmi due to typical herbicides

The excessive application of herbicides on farmlands can substantially reduce labor costs and increase crop yields, but can also have undesirable effects on terrestrial ecosystems. To evaluate the ecological toxicity of herbicides, metolachlor and fomesafen, two typical herbicides that are extensively used worldwide were chosen as target pollutants, and the endogeic earthworm Pheretima guillelmi, which is widely distributed in China, was selected as the test organism. A laboratory-scale microcosmic experiment was set, and energy resources, enzymes, and the composition and connections of intestinal microorganisms in earthworms were determined. Both herbicides depleted the energy resources of the earthworms, especially glycogen contents; increased the levels of antioxidant enzymes; and inhibited acetylcholinesterase. Moreover, the richness and diversity of the intestinal bacterial community of the earthworms were suppressed. Additionally, the bacterial composition at the genus level changed greatly and the connections between dominant bacteria increased dramatically. Most interactions among the bacterial genera belonging to the same and different phyla showed mutualism and competition, respectively. Importantly, metolachlor with higher toxicity had a transitory effect on these indicators in earthworms, whereas fomesafen, with lower toxicity but stronger bioaccumulation potential, exerted a sustaining impact on earthworms. Collectively, these results indicate that the toxic effects of herbicides on terrestrial organisms should be comprehensively considered in combination with biological toxicity, persistence, bioaccumulation potential, and other factors.

Discovery and Biosynthesis of Anthrochelin, a Growth-Promoting Metallophore of the Human Pathogen Luteibacter anthropi

Various human pathogens have emerged from environmental strains by adapting to higher growth temperatures and the ability to produce virulence factors. A remarkable example of a pathoadapted bacterium is found in the genus Luteibacter, which typically comprises harmless soil microbes, yet Luteibacter anthropi was isolated from the blood of a diseased child. Up until now, nothing has been known about the specialized metabolism of this pathogen. By comparative genome analyses we found that L. anthropi has a markedly higher biosynthetic potential than other bacteria of this genus and uniquely bears an NRPS gene locus tentatively coding for the biosynthesis of a metallophore. By metabolic profiling, stable isotope labeling, and NMR investigation of a gallium complex, we identified a new family of salicylate-derived nonribosomal peptides named anthrochelins A-D. Surprisingly, anthrochelins feature a C-terminal homocysteine tag, which might be introduced during peptide termination. Mutational analyses provided insight into the anthrochelin assembly and revealed the unexpected involvement of a cytochrome P450 monooxygenase in oxazole formation. Notably, this heterocycle plays a key role in the binding of metals, especially copper(II). Bioassays showed that anthrochelin significantly promotes the growth of L. anthropi in the presence of low and high copper concentrations, which occur during infections.

Luteibacter flocculans sp. nov., Isolated from a Eutrophic Pond and Isolation and Characterization of Luteibacter Phage vB_LflM-Pluto

Luteibacter is a genus of the Rhodanobacteraceae family. The present study describes a novel species within the genus Luteibacter (EIF3^T). The strain was analyzed genomically, morphologically and physiologically. Average nucleotide identity analysis revealed that it is a new species of Luteibacter. In silico analysis indicated two putative prophages (one incomplete, one intact). EIF3^T cells form an elliptical morphotype with an average length of 2.0 µm and width of 0.7 µm and multiple flagella at one end. The bacterial strain is an aerobic Gram-negative with optimal growth at 30 °C. EIF3^T is resistant towards erythromycin, tetracycline and vancomycin. We propose the name Luteibacter flocculans sp. nov. with EIF3^T (=DSM 112537^T = LMG 32416^T) as type strain. Further, we describe the first known Luteibacter-associated bacteriophage called vB_LflM-Pluto.

Revealing the Tick Microbiome: Insights into Midgut and Salivary Gland Microbiota of Female Ixodes ricinus Ticks

The ectoparasite Ixodes ricinus is an important vector for many tick-borne diseases (TBD) in the northern hemisphere, such as Lyme borreliosis, rickettsiosis, human granulocytic anaplasmosis, or tick-borne encephalitis virus. As climate change will lead to rising temperatures in the next years, we expect an increase in tick activity, tick population, and thus in the spread of TBD. Consequently, it has never been more critical to understand relationships within the microbial communities in ticks that might contribute to the tick's fitness and the occurrence of TBD. Therefore, we analyzed the microbiota in different tick tissues such as midgut, salivary glands, and residual tick material, as well as the microbiota in complete Ixodes ricinus ticks using 16S rRNA gene amplicon sequencing. By using a newly developed DNA extraction protocol for tick tissue samples and a self-designed mock community, we were able to detect endosymbionts and pathogens that have been described in the literature previously. Further, this study displayed the usefulness of including a mock community during bioinformatic analysis to identify essential bacteria within the tick.

Complete Genome Sequence of a Luteibacter Strain Isolated from a Carnivorous Pitcher Plant (Sarracenia minor)

A bacterial isolate of Luteibacter anthropi, designated SM7.4, was isolated from decaying insect detritus inside a carnivorous pitcher plant (Sarracenia minor). Here, we report a complete genome sequence for Luteibacter anthropi strain SM7.4, assembled by combining the Oxford Nanopore MinION flow cell and paired-end Illumina sequencing approaches.

Pinirhizobacter soli gen. nov., sp. nov., a novel low temperature resistant gammaproteobacterium in the family Rhodanobacteraceae isolated from rhizospheric soil of Larix gmelinii

Three yellow-colored strains, NC2-4-308^T, NC3-4-326 and NA3-4-109, were isolated from the rhizosphere soil of Larix gmelinii in Nanwenghe Nature Reserve, Great Khingan, China. These strains were oxidase- and catalase-positive and Gram-staining-negative. The cells were non-motile short rods that were aerobic and non-spore-forming. Growth occurred at pH values of 5.0-8.0 and at 0-4% (w/v) NaCl. The three strains were resistant to low temperature and grew at 2-35 °C. The principal fatty acids (> 5%) were summed feature 9, iso-C_15:0, iso-C_17:0 and anteiso-C_15:0. The predominant quinone was ubiquinone-8. The polar lipids consisted of phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, phosphatidylcholine, two unidentified phospholipids, three unidentified lipids and three unidentified aminophospholipids. The DNA G + C content of the type species was 64.0 mol%. The 16S rRNA gene sequence similarities among the three strains are more than 99.9%, indicating they belong to the same species. Phylogenetic analysis of the 16S rRNA gene, whole-genome sequences, the low ANI (74.2-75.5%) and dDDH (19.3-20.1%) hybridization values enabled differentiation of strains NC2-4-308^T, NC3-4-326 and NA3-4-109 from the members of related genera. The combined data from the morphological, physiological, biochemical and chemotaxonomic tests indicate the three strains as a novel genus and a novel species in the family Rhodanobacteraceae. Therefore, we propose a novel genus with the name Pinirhizobacter soli gen. nov., sp. nov., for which the type strain is NC2-4-308^T (= CFCC 14693^T = KCTC 72394^T).

Rare genera differentiate urban green space soil bacterial communities in three cities across the world

Vegetation complexity is potentially important for urban green space designs aimed at fostering microbial biodiversity to benefit human health. Exposure to urban microbial biodiversity may influence human health outcomes via immune training and regulation. In this context, improving human exposure to microbiota via biodiversity-centric urban green space designs is an underused opportunity. There is currently little knowledge on the association between vegetation complexity (i.e. diversity and structure) and soil microbiota of urban green spaces. Here, we investigated the association between vegetation complexity and soil bacteria in urban green spaces in Bournemouth, UK; Haikou, China; and the City of Playford, Australia by sequencing the 16S rRNA V4 gene region of soil samples and assessing bacterial diversity. We characterized these green spaces as having ‘low’ or ‘high’ vegetation complexity and explored whether these two broad categories contained similar bacterial community compositions and diversity around the world. Within cities, we observed significantly different alpha and beta diversities between vegetation complexities; however, these results varied between cities. Rare genera (<1% relative abundance individually, on average 35% relative abundance when pooled) were most likely to be significantly different in sequence abundance between vegetation complexities and therefore explained much of the differences in microbial communities observed. Overall, general associations exist between soil bacterial communities and vegetation complexity, although these are not consistent between cities. Therefore, more in-depth work is required to be done locally to derive practical actions to assist the conservation and restoration of microbial communities in urban areas.

Complete Genome Sequence of Luteibacter pinisoli MAH-14

Diverse strains of Luteibacter (Gammaproteobacteria) have been isolated from a variety of environments, most frequently in association with both plants and fungi. Motivated by the lack of genomic information for strains throughout the genus Luteibacter, we report here a complete genome sequence for Luteibacter pinisoli strain MAH-14.

Diverse strains of Luteibacter (Gammaproteobacteria) have been isolated from a variety of environments, most frequently in association with both plants and fungi. Motivated by the lack of genomic information for strains throughout the genus Luteibacter, we report here a complete genome sequence for Luteibacter pinisoli strain MAH-14.