Luteimonas wenzhouensis Sp. Nov., A Chitinolytic Bacterium Isolated from a Landfill Soil

Revealing salt concentration for microbial balance and metabolite enrichment in secondary fortified fermented soy sauce: A multi-omics perspective

This study examined the impact of varying salt concentrations on microbiota, physicochemical properties, and metabolites in a secondary fortified fermentation process using multi-omics techniques. It aimed to determine the influence of salt stress on microbiota shifts and metabolic activities. The findings demonstrated that moderate salt reduction (MS) was found to enhance moromi's flavor and quality, while mitigating the negative effects of excessive low salt (LS). MS samples had 1.22, 1.13, and 2.92 times more amino acid nitrogen (AAN), non-volatiles, and volatiles, respectively, than high salt (HS) samples. In contrast, lactic acid and biogenic amines in LS samples were 1.56 g/100 g and 4115.11 mg/kg, respectively, decreasing to 0.15 g/100 g and 176.76 mg/kg in MS samples. Additionally, the contents of ethanol and small peptides increased in MS due to the growth of specific functional microorganisms such as Staphylococcus gallinarum, Weissella confusa, and Zygosaccharomyces rouxii, while food-borne pathogens were inhibited. Network analysis revealed that the core microbial interactions were enhanced in MS samples, promoting a balanced fermentation environment. Redundancy analysis (RDA) and correlation analyses underscored that the physicochemical properties significantly impacted bacterial community structure and the correlations between key microbes and flavor compounds. These findings provided a theoretical foundation for developing innovative reduced-salt fermentation techniques, contributing to the sustainable production of high-quality soy sauce.

The host sex contributes to the endophytic bacterial community in Sargassum thunbergii and their receptacles

Endophytic bacteria have a complex coevolutionary relationship with their host macroalgae. Dioecious macroalgae are important producers in marine ecosystems, but there is still a lack of research on how sex influences their endophytic bacteria. In this study, the endophytic bacterial communities in male and female S. thunbergii and their reproductive tissues (receptacles) were compared using culture methods and high-throughput sequencing. The endophytic bacterial communities detected by the two methods were different. Among the 78 isolated strains, the dominant phylum, genus, and species were Bacillota, Alkalihalobacillus, and Alkalihalobacillus algicola, respectively, in the algal bodies, while in the receptacles, they were Bacillota, Vibrio, and Vibrio alginolyticus. However, 24 phyla and 349 genera of endophytic bacteria were identified by high-throughput sequencing, and the dominant phylum and genus were Pseudomonadota and Sva0996_ Marine_ Group, respectively, in both the algal body and the receptacles. The two methods showed similar compositions of endophytic bacterial communities between the samples of different sexes, but the relative abundances of dominant and specific taxa were different. The high-throughput sequencing results showed more clearly that the sex of the host alga had an effect on its endophyte community assembly and a greater effect on the endophytic bacterial community in the receptacles. Moreover, most specific bacteria and predicted functional genes that differed between the samples from the males and females were related to metabolism, suggesting that metabolic differences are the main causes of sex differences in the endophytic bacterial community. Our research is the first to show that host sex contributes to the composition of endophytic bacterial communities in dioecious marine macroalgae. The results enrich the database of endophytic bacteria of dioecious marine macroalgae and pave the way for better understanding the assembly mechanism of the endophytic bacterial community of algae.

Three novel Luteimonas species from a root and rhizosphere soil of Kalidium cuspidatum: Luteimonas endophytica sp. nov., Luteimonas rhizosphaericola sp. nov. and Luteimonas kalidii sp. nov

Three Gram-stain-negative, aerobic and rod-shaped bacterial strains, designated RD2P54T, M1R5S18T and M1R5S59T, were isolated from a root and rhizosphere soil of Kalidium cuspidatum, in Baotou, PR China. The three strains showed 94.1–98.7 % 16S rRNA gene sequence similarities to Luteimonas strains, indicating they belonged to the genus Luteimonas . The phylogenomic tree based on core genomes showed that strain RD2P54T tightly clustered with Luteimonas salinisoli SJ-92T, while strains M1R5S18T and M1R5S59T clustered with each other and with Luteimonas viscosa XBU10T and Luteimonas saliphila SJ-9T. Though strains M1R5S18T and M1R5S59T showed high 16S rRNA similarity (99.4 %) to each other, the low average nucleotide identity based on blast (ANIb; 88.6 %) and digital DNA–DNA hybridization (dDDH; 31.6 %) values between them indicated that they belonged to two different species. The ANIb and dDDH values of strains RD2P54T, M1R5S18T and M1R5S59T with their closely neighbours are well below the delineation threshold values for identifying strains as representing different species. All three strains take iso-C15 : 0 and summed feature 9 (C16 : 0 10-methyl and/or iso-C17 : 1  ω9c) as major fatty acids, and ubiquinone-8 as the sole respiratory quinone. The major polar lipids of all three strains are diphosphatidylglycerol, phosphatidylglycerol and phosphatidylethanolamine. Based on phenotypic and phylogenetic data, these three strains should be considered to represent three novel species of the genus Luteimonas , for which the names Luteimonas endophytica sp. nov. (type strain RD2P54T=CGMCC 1.61535T =KCTC 92470T), Luteimonas rhizosphaericola sp. nov. (type strain M1R5S18T=CGMCC 1.61537T =KCTC 92469T) and Luteimonas kalidii sp. nov. (type strain M1R5S59T=CGMCC 1.61536T =KCTC 92471T) are proposed.

Characterization of the responses of soil micro-organisms to azoxystrobin and the residue dynamics of azoxystrobin in wheat-corn rotation fields over two years

Azoxystrobin, a high-efficiency and broad-spectrum strobilurin fungicide, has been widely used in global agricultural production. However, the effects of azoxystrobin on soil micro-organisms have scarcely been studied, and relevant experiments are usually conducted under laboratory conditions using active ingredient. Therefore, the effects of azoxystrobin on soil micro-organisms when applied to actual farmland are unknown. We sought to address this knowledge gap in this study, where we studied the effects of azoxystrobin on soil micro-organisms in a wheat-corn rotation field over two years. The results indicate that after two years of azoxystrobin application the activities of soil enzymes were inhibited, and the abundance of functional genes related to the nitrogen and carbon cycle were inhibited, which change the abundance of soil microbial bacteria of genera. As a consequence, the soil nitrogen and carbon cycles were disturbed. In addition, azoxystrobin inhibited the abundance of functional bacteria related to organic pollutant degradation and soil metabolism, where the rate of azoxystrobin degradation diminished over time. Moreover, azoxystrobin significantly inhibited the soil-culturable microbial population. The integrated biomarker response (IBR) indicated that the soil-culturable microbial population can be used as a sensitive indicator of the effect of azoxystrobin on soil micro-organisms. The final levels of azoxystrobin residues measured in grains were less than 0.004 mg/kg, lower than the maximum residue limits in European Union and China. The results of this study provide a basis for suggestions regarding the appropriate use of azoxystrobin in addition to support for elucidating the interaction between biological macromolecules and pollutants.

Rotations improve the diversity of rhizosphere soil bacterial communities, enzyme activities and tomato yield

The use of rotations is an effective strategy to control crop diseases and improve plant health. The soil bacterial communities in the rhizosphere are highly important for maintaining soil productivity. However, the composition and structure of soil bacterial communities in the rotations of vegetable crops remain unclear. In this study, we explored the bacterial diversity and community structure of the tomato rhizosphere, including enzyme activities, yield, and fruit quality, under three different cropping systems: tomato-tomato (Solanum lycopersicum) continuous cropping (TY1), eggplant (Solanum melongena)-tomato rotation (TY2) and arrowhead (Sagittaria trifolia)-tomato rotation (TY3). The composition and diversity of the rhizosphere bacterial communities differed significantly. The diversity was more in the TY2 and TY3 treatments than those in the TY1 treatment. Chujaibacter and Rhodanobacter were two predominant and unique strains detected only in TY1, while the relative abundances of Curvibacter and Luteimonas were the highest in TY2 and TY3, respectively. Moreover, Lysobacter was a relatively abundant type of biocontrol bacterium found only in the TY3 treatment, which could contribute to alleviating the obstacle of tomato continuous cropping. Compared with the TY1 treatment, the activities of catalase were significantly higher in the TY2 and TY3 treatments. In addition, compared with TY1, the TY2 and TY3 plots increased the following parameters: tomato yields by 24-46%, total soluble solids by 37-93%, total organic acid by 10-15.7% and soluble protein by 10-21%, while the content of nitrate was significantly reduced by 23%. Altogether, compared with the tomato monoculture, the rotations of tomato with eggplant and arrowhead shifted the rhizosphere bacterial communities and improved the yield and quality of the tomato. Moreover, a tomato rotation, particularly with arrowhead, was an effective way to alleviate the obstacles of continuous cropping.

Luteimonas saliphila sp. nov. and Luteimonas salinisoli sp. nov., two novel strains isolated from saline soils

Two Gram-stain-negative, motile with single polar flagellum, rod-shaped bacterial strains, named SJ-9T and SJ-92T, were isolated from saline soils from Inner Mongolia, PR China. SJ-9T and SJ-92T grew at pH 6.5–10.0 and 7.0–11.0, 10–35 °C, and in the presence of 0–5 % and 0–8 % NaCl, respectively. Both strains were positive for oxidase, and negative for catalase. The results of phylogenetic analysis based on 16S rRNA gene sequences indicated that SJ-9T clustered with Luteimonas marina FR1330T (sharing 97.9 % 16S rRNA gene similarity), Luteimonas huabeiensis HB2T (96.5 %), ‘Luteimonas wenzhouensis’ YD-1 (96.6 %), and Luteimonas composti CC-YY255T (95.1 %), and shared low 16S rRNA gene similarities (<97.0 %) with all the other type strains; while SJ-92T clustered with Luteimonas aestuarii B9T (98.2 %), and shared low 16S rRNA gene similarities (<98.0 %) with all the other type strains. The two strains shared 97.4 % 16S rRNA gene similarity with each other. The major cellular fatty acids of both strains are iso-C15 : 0 and summed feature 9 (C16 : 0 10-methyl and/or iso-C17 : 1ω9c). The major polar lipids of both strains are diphosphatidylglycerol, phosphatidylglycerol and phosphatidylethanolamine. The only respiratory quinone for both strains is ubiquinone-8 (Q-8). The genomic DNA G+C contents are 69.3 and 70.4 mol%, respectively. The digital DNA–DNA hybridization (dDDH) and average nucleotide identity by blast (ANIb) values between the two strains were 22.6 and 77.5 %, while the values between SJ-9T and ‘L. wenzhouensis’ YD-1, L. marina FR1330T, and L. huabeiensis HB2T were 38.1, 39.2, and 21.9 %, and 82.5, 84.4, and 78.5 %, while those between SJ-92T and L. aestuarii B9T were 21.3 and 76.7 %. On the basis of the phenotypic, physiological and phylogenetic results, SJ-9T and SJ-92T represent two novel species of the genus Luteimonas , for which the names Luteimonas saliphila [type stain SJ-9T (=CGMCC 1.17377T=KCTC 82248T)] and Luteimonas salinisoli [type strain SJ-92T (=CGMCC 1.17695T=KCTC 82208T)] are proposed.

Metagenomics Analysis Reveals the Microbial Communities, Antimicrobial Resistance Gene Diversity and Potential Pathogen Transmission Risk of Two Different Landfills in China

In this study, we used a metagenomic approach to analyze microbial communities, antibiotic resistance gene diversity, and human pathogenic bacterium composition in two typical landfills in China. Results showed that the phyla Proteobacteria, Bacteroidetes, and Actinobacteria were predominant in the two landfills, and archaea and fungi were also detected. The genera Methanoculleus, Lysobacter, and Pseudomonas were predominantly present in all samples. sul2, sul1, tetX, and adeF were the four most abundant antibiotic resistance genes. Sixty-nine bacterial pathogens were identified from the two landfills, with Klebsiella pneumoniae, Bordetella pertussis, Pseudomonas aeruginosa, and Bacillus cereus as the major pathogenic microorganisms, indicating the existence of potential environmental risk in landfills. In addition, KEGG pathway analysis indicated the presence of antibiotic resistance genes typically associated with human antibiotic resistance bacterial strains. These results provide insights into the risk of pathogens in landfills, which is important for controlling the potential secondary transmission of pathogens and reducing workers’ health risk during landfill excavation.

Heterotrophic nitrification and related functional gene expression characteristics of Alcaligenes faecalis SDU20 with the potential use in swine wastewater treatment

A new heterotrophic nitrifying bacterium was isolated from the compost of swine manure and rice husk and identified as Alcaligenes faecalis SDU20. Strain SDU20 had heterotrophic nitrification potential and could remove 99.7% of the initial NH₄⁺-N. Nitrogen balance analysis revealed that 15.9 and 12.3% of the NH₄⁺-N were converted into biological nitrogen and nitrate nitrogen, respectively. The remaining 71.44% could be converted into N₂ or N₂O. Single-factor experiments showed that the optimal conditions for ammonium removal were the carbon source of sodium succinate, C/N ratio 10, initial pH 8.0, and temperature 30 °C. Nitrification genes were determined to be upregulated when sodium succinate was used as the carbon source analyzed by quantitative real-time polymerase chain reaction (qRT-PCR). Strain SDU20 could tolerate 4% salinity and show resistance to some heavy metal ions. Strain SDU20 removed 72.6% high concentrated NH₄⁺-N of 2000 mg/L within 216 h. In a batch experiment, the highest NH₄⁺-N removal efficiency of 98.7% and COD removal efficiency of 93.7% were obtained in the treatment of unsterilized swine wastewater. Strain SDU20 is promising in high-ammonium wastewater treatment.