We herein exami­ned the inoculation effects of indigenous Bradyrhizobium diazoefficiens isolates on the growth and yield of adzuki beans and their competition with other bradyrhizobia using pot and field experiments. In the pot experiment, shoot nitrogen content was significantly higher following inoculations with AMP1 and Bd (a mixture of AN9 and AN20) than with the control. Furthermore, a correlation was observed between shoot nitrogen content and shoot dry weight. In the field experiment, the inoculating isolates did not significantly affect growth or yield. However, an interaction effect was observed in pod numbers and yield, suggesting that the effects of inoculation varied depending on the cultivar and inoculating isolate. In the correlation ana­lysis, pod number correlated with node number and nodule number. Similarly, yield correlated with shoot length, node number, nodule number, and pod number. Regarding competition between inoculated isolates and other strains, B. elkanii was dominant in pot and field experiments. To enhance the yield of adzuki bean through inoculations, it is necessary to overcome competition from indigenous B. elkanii and increase the occupancy rate of B. diazoefficiens isolates.

The present study proposes a categorization of bacteria that leak from activated sludge processes to secondary treated water (STW). Bacterial populations in primary treated water (PTW), activated sludge (AS), STW, and the 0.2‍ ‍μm-filtrate of STW (FSTW) in a full-scale wastewater treatment plant with two treatment trains were observed for a period of one year using a 16S rRNA ana­lysis approach. The taxonomic groups detected were categorized as different “leak types” based on the read occupancies in PTW, AS, STW, and FSTW, where a leak type indicates the likelihood of a taxonomic group to leak to STW. Five leak types were introduced: “LTE”, “LTE-I”, “LTEF”, “LTF”, and “NLT”, with “LT” for leak type, “E” for high read occupancy in STW or the effluent of secondary settling tanks, “I” for high read occupancy in PTW or influent to the AS process, “F” for high read occupancy in FSTW, and “NLT” for a smaller likelihood to leak. Representative taxonomic groups for each leak type were Neisseria and ABY1 for “LTE” Parcubacteria for “LTEF”, Campylobacterota for “LTE-I”, and Saccharimonadia, Bdellovibrionota, and some lineages in Comamonadaceae for “LTF”. Although some taxonomic groups, such as Comamonadaceae, included different leak types, the categorization assigned to each taxonomic group was mostly consistent between the two treatment trains. The categorization scheme proposed herein may become a useful key for understanding the characteristics of bacteria that appear in AS and STW.

Ascetosporeans are parasitic protists of invertebrates. A deep sequencing ana­lysis of species within the orders Mikrocytida, Paramyxida, and Haplosporida using metagenomic approaches revealed that their mitochondria were functionally reduced and their organellar genomes were lacking. Ascetosporeans belonging to the order Paradinida have not been sequenced, and the nature of their mitochondria remains unclear. We herein established two cultures of Paradinida and conducted DNA and RNA sequencing ana­lyses. The results obtained indicate that mitochondrial function in paradinids was not reduced and their organellar genomes were retained. In contrast, their mitochondrial genomes were involved in massive A-to-I and C-to-U substitution types of RNA editing. All edits in protein-coding genes were nonsynonymous substitutions, and likely had a restorative function against negative mutations. Furthermore, we detected possible sequences of DYW type of pentatricopeptide repeat (PPR-DYW) protein and a homologue of adenosine deaminase acting on RNA (ADAR-like), which are key enzymes for C-to-U and A-to-I substitutions, respectively. An immunofluorescence ana­lysis showed that ADAR-like of paradinids may specifically localize within mitochondria. These results expand our knowledge of the diversity and complexity of organellar RNA editing phenomena.

Soil nutrient loss from intensive farming is a critical issue in sub-Saharan Africa that affects food security. While soil microbial nitrification supplies available nitrogen, excessive nitrification leads to nitrogen loss. However, the species driving nitrification and their functions in this region remain largely unknown. Therefore, we investigated the responses of ammonia-oxidizing bacterial (AOB) and archaeal (AOA) communities to land-use changes in Zambia and their relationship with nitrification potential. Soil samples were collected from three sites in Zambia that all had neighboring natural and farmed (maize) lands. We measured nitrification potential, quantified AOB and AOA, and analyzed these communities by targeting the ammonia monooxygenase subunit A (amoA) gene, which encodes a key enzyme in nitrification. Nitrification potential was 1.51-fold higher in farmlands than in natural lands. AOB abundance tended to be greater in farmlands, whereas AOA abundance was smaller. Farming changed the AOB community structure, increasing Nitrosospira cluster 3a.2 at the three sites, while minor site-specific responses were also observed. In contrast, the AOA community structure was not significantly different between land uses, but varied among sites, with cluster NS-ζ being more prominent in one site with neutral soil (pH 7.64) than in the other sites (pH 5.70 and 5.71). These results suggest that AOA species were generally vulnerable to farming, decreasing in abundance without structural changes, while some AOB species increased, driving changes in their community structure. These insights are fundamental for understanding soil nitrogen depletion due to microbial changes under farming and are crucial for developing sustainable land-use practices in sub-Saharan Africa.

Frankia spp. are multicellular actinobacteria with the ability to fix atmospheric dinitrogen (N₂). Frankia fixes N₂ not only in the free-living state, but also in root-nodule symbioses with more than 200 plant species called actinorhizal plants. In the present study, we isolated mutants of the pyrE (orotate phosphoribosyltransferase) and pyrF (orotidine-5′-phosphate decarboxylase) genes in Frankia casuarinae strain CcI3 using gamma rays as a mutagen and systematically identified the types of mutations that occurred in these genes. pyrEF mutants were isolated as uracil auxotrophs using the antimetabolite 5-fluoroorotic acid. We elucidated the nucleotide sequences of the pyrEF genes in 32 uracil auxotrophs, and detected eight substitutions, 17 single-nucleotide deletions, and seven large insertions. Large insertions were insertion sequences (IS elements); four belonged to the IS4 family, two to the IS66 family, and one to the IS110 family. This is the first study to demonstrate the mobilization of IS elements in the Frankia genome.

The present study exami­ned bacteria that anaerobically degrade the aromatic compound, benzoate, and obtained enrichment cultures from marine sediments under illumination. The enrichment culture contained anoxygenic photosynthetic bacteria and non-photosynthetic bacteria. The photosynthetic strain PS1, a purple sulfur bacterium in the genus Marichromatium, was unable to utilize benzoate; however, when combined with the non-photosynthetic bacterial isolate, Marinobacterium sp. strain BA1, the co-culture grew anaerobically on benzoate in the presence of thiosulfate or tetrathionate. Based on the metabolic profiles of the co-culture and axenic cultures, the following syntrophic interactions were proposed. Strain PS1 oxidizes thiosulfate as the electron source for photosynthesis to produce tetrathionate and relies on carbon dioxide produced through benzoate degradation by strain BA1. Strain BA1 oxidizes benzoate and reduces tetrathionate to provide thiosulfate to strain PS1 for photosynthetic carbon fixation. To the best of our knowledge, this is the first study to report anaerobic benzoate degradation in a photosynthetic co-culture through the syntrophic exchange of sulfur compounds.

The present study aimed to isolate and characterize a marine bacterium capable of passing through a 0.1-μm pore-sized filter (0.1-μm filter). Sediment suspension samples were filtered through 0.1-μm filters, inoculated into sterile media, and incubated. Isolated SspURN76 belonged to Saccharospirillum, according to 16S rRNA gene sequencing, and showed a very slender shape. The minimum cell size of SspURN76 was 0.09×3.2‍ ‍μm. These morphological features of SspURN76 were likely responsible for its passage through 0.1-μm filters. Based on the results obtained herein, marine bacteria may be present in 0.1-μm filtered fractions.

Clostridium spp. are anaerobic, Gram-positive, spore-forming bacteria comprising more than 150 species, some of which are important pathogens of humans and animals. Members of this genus have been isolated from a number of environments, but are rarely found in the atmosphere. In the present study, we exami­ned culturable airborne Clostridium spp. and clarified their pathogenicity. We obtained 19 culturable Clostridium isolates from size-fractionated samples collected at a suburban site in Toyama, central Japan. Culturable Clostridium spp. were detected in particles larger than 1.1‍ ‍μm, and the size distribution peaked at 2.1–3.3‍ ‍μm, corresponding to the spore size of Clostridium spp. More Clostridium spp. were detected in coarse particles >2.1‍ ‍μm not only by culture methods, but also by 16S rRNA gene amplicon sequencing. Whole-genome sequencing (WGS) identified seven Clostridium species, among which Clostridium perfringens was predominant. Moreover, WGS revealed that C. perfringens isolates harbored many virulence and antibiotic resistance genes with the potential to cause gas gangrene. The detection and characterization of potential airborne pathogens are crucial for preventing the spread of diseases caused by these pathogens. To the best of our knowledge, this is the first study to demonstrate that anaerobic Clostridium spp. may be transported under aerobic conditions in the atmosphere and pose potential risks to human health.