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PubMed2026

Description of two nitrogen-fixing bacteria, Azospirillum mesophilum sp. nov. and Azospirillum terrae sp. nov., isolated from paddy soils.

Two novel aerobic, rod-shaped, motile bacterial strains, designated as sgz302134T and sgz301742T, were isolated from paddy soil in Fujian Province. Strains sgz302134T and sgz301742T shared the highest 16S rRNA gene sequence similarities with the type strains Azospirillum isscasi C340-1T (98.2%) and Azospirillum thiophilum DSM 21654T (97.4%), respectively. The phylogenetic tree based on 16S rRNA gene sequences showed that two strains clustered with members of the genus Azospirillum. Growth of strains sgz302134T and sgz301742T was observed at 10-45 °C, pH 5.0-9.5 and 0-0.5% (w/v) NaCl and 15-37 °C, pH 6.0-9.0 and 0-1.0% (w/v) NaCl, respectively. Strains sgz302134T and sgz301742T contained Q-10 as the main quinone. The main fatty acids (>10%) of both strains were summed feature 2 (C12 : 0 aldehyde), summed feature 3 (C16 : 1 ω7c and/or C16 : 1 ω6c), summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c) and C16 : 0. The genomic DNA G+C content of strains sgz302134T and sgz301742T was 68.4 and 68.3%, respectively. The digital DNA-DNA hybridization and average nucleotide identity values between the two strains and their related reference strains were 27.8 and 87.4% and 22.0 and 84.3%, respectively. Both strains possessed nif genes nifBDEHKN. Based on the above results, these two strains represent two novel species of the genus Azospirillum, for which the names Azospirillum mesophilum sp. nov. and Azospirillum terrae sp. nov. are proposed. The type strains are sgz302134T (=MCCC 1K09520T=KCTC 8840T) and sgz301742T (=MCCC 1K09804T=KCTC 18149T), respectively.

Soil Microbiology↗
PubMed2026

Improving quality control of microbial agri-inputs by confirming strain identity with an easy and low-cost PCR-multiplex: A study case with Azospirillum brasilense.

The first commercial product containing the Azospirillum brasilense elite strains Ab-V5 and Ab-V6 was launched in Brazil in 2009. These strains have demonstrated agronomic efficiency in grasses and in legume co-inoculation, accounting for approximately 43 million doses in 2024. Official identification of these strains is currently performed by rep-PCR, a reliable but time-consuming and laborious method. In this study, a multiplex PCR assay was developed for the simultaneous identification of Ab-V5 and Ab-V6 in a single reaction using strain-specific SNPs. Forward primers were designed so that the terminal nucleotide at the 3' end corresponded to a strain-specific SNP unique to each target strain. To further enhance specificity, artificial mismatches were introduced at the fourth nucleotide from the 3' end of the forward primers. SNPs were identified using Snippy based on genomic alignments between Ab-V5 and Ab-V6 and confirmed by local BLASTn against the genomes of other Azospirillum species. In the multiplex assay, simultaneous and specific amplification of both strains was observed in a single reaction, without non-specific amplification. Primer specificity was also experimentally evaluated against other A. brasilense strains (Ab-V1, Ab-V2, Ab-V4, Ab-V7, Ab-V8, and Sp7T), in silico against bacteria from different genera associated with agricultural inoculants, and in commercial inoculant samples containing Ab-V5 and Ab-V6. The results confirmed the high specificity of the primers for Ab-V5 and Ab-V6 and demonstrated that the assay was capable of identifying the strains in commercial inoculants. This assay facilitates inoculant quality control by enabling strain confirmation using a simple, rapid, and low-cost method.

Azospirillum↗
PubMed2026

Amplicon and metagenomic sequencing reveal thifluzamide drive rhizosphere microbial structural shifts and functional adaption.

Thifluzamide (TF) is a widely used phenyl urea fungicide in rice production; however, its impacts on the structural composition and functional dynamics of the rhizosphere microbiome remain poorly understood. Here, we systematically investigated the effects of TF on the structure, interactions, and functional potential of the rice (Oryza sativa L.) rhizosphere microbiome using integrated amplicon sequencing and metagenomic approaches. TF application significantly altered both bacterial and fungal community composition, bacterial diversity was markedly reduced, whereas fungal diversity increased. With bacterial diversity markedly reduced while fungal diversity increased. Beta-diversity analyses revealed strong treatment-driven community separation, indicating pronounced TF-induced microbial restructuring. Co-occurrence network analysis demonstrated reduced complexity and connectivity in bacterial networks but increased negative co-occurrence patterns within fungal communities, suggesting contrasting stability responses between microbial kingdoms. Metagenomic profiling further revealed substantial functional shifts, including the differential enrichment of KEGG and COG pathways associated with xenobiotic metabolism. Notably, while total ARG abundance remained stable, TF exposure altered the resistome profile by selectively enriching specific classes of antibiotic resistance genes (ARGs), biocide resistance genes (BRGs), and mobile genetic elements (MGEs). Strong positive correlations between MGEs and ARGs highlighted an elevated potential for horizontal gene transfer. Metagenome-assembled genome (MAG) analysis identified specific TF-enriched bacterial taxa, including Methylophilus, Sulfurospirillum, and Azospirillum, which harbored genes involved in pesticide degradation and xenobiotic transformation. Collectively, these findings demonstrate that TF profoundly reshapes the rice rhizosphere microbiome by altering microbial diversity, interaction networks, resistance gene profiles, and functional capacities. This study provides genomic insights into fungicide-microbiome interactions, underscoring the potential ecological implications associated with TF application, while identifying candidate microbial taxa that may contribute to pesticide degradation and rhizosphere microecology resilience.

Rhizosphere↗