Mutualism between bacteria and eukaryotes has essential roles in the history of life, but the evolution of their compatibility is poorly understood. Here we show that different Sinorhizobium strains can form either nitrogen-fixing nodules or uninfected pseudonodules on certain cultivated soybeans, while being all effective microsymbionts of some wild soybeans. However, a few well-infected nodules can be found on a commercial soybean using inocula containing a mixed pool of Tn5 insertion mutants derived from an incompatible strain. Reverse genetics and genome sequencing of compatible mutants demonstrated that inactivation of T3SS (type three secretion system) accounted for this phenotypic change. These mutations in the T3SS gene cluster were dominated by parallel transpositions of insertion sequences (ISs) other than the introduced Tn5. This genetic and phenotypic change can also be achieved in an experimental evolution scenario on a laboratory time scale using incompatible wild-type strains as inocula. The ISs acting in the adaptive evolution of Sinorhizobium strains exhibit broader phyletic and replicon distributions than other ISs, and prefer target sequences of low GC% content, a characteristic feature of symbiosis plasmid where T3SS genes are located. These findings suggest an important role of co-evolved ISs in the adaptive evolution of rhizobial compatibility.

Aiming to reduce synthetic fertilizer dependence and enhance soil fertility, this study isolated and characterized nitrogen-fixing bacteria from the maize rhizosphere. Nitrogen-free selective media were used for bacterial isolation, followed by detection of the nifH gene and nitrogenase activity. Phylogenetic identification was conducted via 16S rRNA sequencing. Growth-promoting traits, stress tolerance, and pot-based plant inoculation effects were assessed. Genetic modification of strain GN8811 was performed to improve nitrogen fixation and growth promotion. Seven isolates that carried the nifH gene and exhibited nitrogenase activity were closely related to four genera. Several isolates showed phosphate solubilization, iron chelation, IAA production, or potassium solubilization, with GN2003 and GN8811 tolerating high salinity and variable pH. Inoculation with GN8811 promoted maize growth comparable to nitrogen fertilization, and its genetically modified derivative (ΔnifL:PrpoD) showed further improvement even under high nitrogen conditions. These findings highlight the potential of combining microbial screening with genetic engineering to develop efficient bioinoculants for sustainable maize cultivation.

Functional microbial agents play a crucial role in various fields such as agriculture, feed fermentation, aquaculture, and environmental protection. However, traditional microbial agents were confronted with critical challenges such as limited shelf-life, reduced activity, and inconsistent efficacy. In this case, we innovatively proposed the concept of Directed Micro-Ecology (DME) and developed its application system, including a core module named DME intelligent fermentor (DME25). Over 40 functional strains, including bacterial strains and fungus strains, were successfully cultured to 10∼50 ×10 ⁸ CFU/mL within 20∼48 h and maintained a relatively low contamination rate (<2.5%). Finally, the stability and effectiveness of these DME-fermented strains were validated in different application areas, all of which exhibited perfect functional characteristics. Firstly, the bacillus strains inhibited the progression of wilt disease and significantly improved the growth of tomatoes. Secondly, all tested lactobacillus strains improved the nutrition and quality of fermented feed, complying with feed industry standards. Lastly, the ammonia nitrogen concentration, nitrite concentration of aquaculture water and phosphate concentration, COD of aquaculture tail water were significantly reduced within 1∼4 d. The successful application of the DME intelligent fermentor in different fields marks a pivotal breakthrough in technological innovation of microbial agents on-site one-step fermentation. This technological advancement opens new avenues for enhancing the stability and effectiveness of microbial agents, infusing powerful impetus to the development of microbial application.

(Background) Aiming to reduce synthetic fertilizer dependence and enhance soil fertility, this study isolated and characterized nitrogen-fixing bacteria from the maize rhizosphere. (Methods) Nitrogen-free selective media were used for bacterial isolation, followed by detection of the nifH gene and nitrogenase activity. Phylogenetic identification was conducted via 16S rRNA sequencing. Growth-promoting traits, stress tolerance, and pot-based plant inoculation effects were assessed. Genetic modification of strain GN8811 was performed to improve nitrogen fixation and growth promotion. (Results) Seven isolates that carried the nifH gene and exhibited nitrogenase activity were closely related to four genera. Several isolates showed phosphate solubilization, iron chelation, IAA production, or potassium solubilization, with GN2003 and GN8811 tolerating high salinity and variable pH. Inoculation with GN8811 promoted maize growth comparable to nitrogen fertilization, and its genetically modified derivative (ΔnifL::PrpoD) showed further improvement even under high nitrogen conditions. (Conclusions) These findings highlight the potential of combining microbial screening with genetic engineering to develop efficient bioinoculants for sustainable maize cultivation.