Nitrous oxide (N2O) is a potent greenhouse gas, and its largest anthropogenic source is agricultural soils. In these soils, N2O emissions are produced from nitrogen fertilization and nitrogen-rich crop residues, such as soybean nodules. Previous studies demonstrated that inoculation with Bradyrhizobium diazoefficiens possessing the N2O reductase gene (nosZ) effectively mitigated N2O emissions from soybean fields at harvest. More recently, Bradyrhizobium ottawaense, which exhibits higher nosZ expression, reduced N2O emissions more effectively than B. diazoefficiens during the degradation of soybean nodules formed under sterile vermiculite conditions. Although the effects of inoculation with B. ottawaense have subsequently been exami-ned under natural soil conditions, it remains unclear whether these effects are maintained across different soil types and soybean cultivars. Therefore, we herein investigated the effects of inoculation with B. ottawaense on its competitiveness and N2O emissions in pot experiments using two field soils (Andosol and Fluvisol) and three Japanese commercial soybean cultivars ('Hatayutaka', 'Yukihomare R', and 'Satonohohoemi'). The results demonstrated that inoculation with B. ottawaense significantly increased higher nodule occupancy of the inoculant strain compared with the non-inoculated controls in the two field soils. Moreover, B. ottawaense tended to reduce N2O emissions in Andosol dominated by nosZ-lacking bradyrhizobia, regardless of the soybean cultivar. No significant N2O-reducing effects were observed in Fluvisol dominated by nosZ-possessing bradyrhizobia. Collectively, these results suggest the applicability of inoculation with B. ottawaense to diverse soybean cultivars and its effectiveness in mitigating N2O emissions from soybean fields in which indigenous nosZ-lacking bradyrhizobial populations are dominant, such as Andosols.
Sugarcane for traditional Wasanbon sugar has long been cultivated in Higashi-Kagawa. Three sugarcane cultivars were cultivated at three sites in Kagawa Prefecture, and root-associated bacterial communities were analyzed using 16S rRNA gene amplicon sequencing. Bacterial community compositions varied primarily according to the cultivation site rather than the cultivar, and soil bacterial communities showed similar site-dependent clustering patterns. These results indicate that the cultivation site affects the root-associated bacterial community structure.
The plant microbiota plays important roles in plant responses to biotic and abiotic stresses. Wasabi (Eutrema japonicum), a traditional crop indigenous to Japan, remains poorly characterized in terms of its associated bacterial community. In the present study, 16S rRNA gene amplicon sequencing revealed distinct bacterial community structures across plant and soil compartments. The rhizome microbiota, the edible plant organ used as a spice, exhibited intermediate characteristics between those of the root and leaf microbiota. These results provide fundamental insights into the wasabi-associated bacterial microbiota and identify the rhizome as a distinct microbial niche.
Individuals who regularly handle specific chemicals may harbor microorganisms capable of metabolizing those compounds. Such hands may therefore provide a practical route for obtaining functional microorganisms from easily accessible human-associated environments. In this study, we found that nearly 90% of professional dyers harbored dye-decolorizing bacteria, which were efficiently isolated from their fingertips, with 20% of isolates exhibiting decolorizing activity. These strains showed distinct genus-level profiles. These findings indicate that occupational exposure to dyes strongly enriches dye-decolorizing bacteria, suggesting that the hands of textile workers may serve as a source for isolating microorganisms with potential applications in dye bioremediation.
Since 2018, foot rot disease caused by Diaporthe destruens has emerged as a serious threat to sweet potato production in Japan. Although plant-associated bacteria have been suggested to contribute to disease suppression, the bacterial community structure of asymptomatic sweet potato tubers in foot rot-infested fields remains unclear. In the present study, we analyzed the bacterial communities of asymptomatic tubers collected adjacent to infected tubers from four foot rot-infested fields. Thirteen bacterial taxa with >1% relative abundance were detected, among which Enterobacter (ASV-129 sequence; 427 bp) was dominant, accounting for an average of 49.4% of total 16S rRNA gene amplicon reads. Forty bacterial strains were isolated from asymptomatic sweet potato tubers using R2A agar plates. Among them, strain 12CK showed 100% sequence identity to ASV-129 and was identified as Enterobacter hormaechei based on a genome anal-ysis (genome size: 4,832,483 bp). In the present study, D. destruens 2YO was also isolated from infected plants, and its pathogenicity was confirmed. In growth inhibition assays (dual culture assay), E. hormaechei 12CK strongly inhibited the growth of D. destruens 2YO. Pot and field trials will be required to examine the applicability of strain 12CK as a microbial biocontrol agent.
