Absorption, translocation, and effects of Bt Cry1Ac peptides from transgenic cotton to the intercrops and soil functional bacteria

Halotolerant Enterobacter asburiae A103 isolated from the halophyte Salix linearistipularis: Genomic analysis and growth-promoting effects on Medicago sativa under alkali stress

Soil salinization negatively affects plant growth and threatens food security. Halotolerant plant growth-promoting bacteria (PGPB) can alleviate salt stress in plants via diverse mechanisms. In the present study, we isolated salt-tolerant bacteria with phosphate-solubilizing abilities from the rhizosphere of Salix linearistipularis, a halophyte distributed in saline-alkali soils. Strain A103 showed high phosphate solubilization activity and was identified as Enterobacter asburiae based on genome analysis. In addition, it can produce indole-3-acetic acid (IAA), siderophores, and 1-aminocyclopropane-1-carboxylate (ACC) deaminase. Genome mining has also revealed the presence of several functional genes involved in the promotion of plant growth. Inoculation with A103 markedly improved alfalfa growth in the presence of 100 mM NaHCO3. Under alkali stress, the shoot and root dry weights after bacterial inoculation improved by 42.9 % and 21.9 %, respectively. Meanwhile, there was a 35.9-37.1 % increase in the shoot and root lengths after treatment with A103 compared to the NaHCO3-treated group. Soluble sugar content, peroxidase and catalase activities increased in A103-inoculated alfalfa under alkaline stress. A significant decrease in the malondialdehyde content was observed after treatment with strain A103. Metabolomic analysis indicated that strain A103 positively regulated alkali tolerance in alfalfa through the accumulation of metabolites, such as homocarnosine, panthenol, and sorbitol, which could reduce oxidative damage and act as osmolytes. These results suggest that halophytes are valuable resources for bioprospecting halotolerant beneficial bacteria and that the application of halotolerant growth-promoting bacteria is a natural and efficient strategy for developing sustainable agriculture.

Impact of Transgenic Maize Ruifeng125 on Diversity and Dynamics of Bacterial Community in Rhizosphere Soil

With the development of commercialized planting of genetically modified crops, their ecological security risks remain a key topic of public concern. Insect-resistant genetically modified maize, Ruifeng125, which expresses a fusion Bt protein (Cry1Ab-Cry2Aj), has obtained the application safety certificate issued by the Chinese government. To determine the effects of Ruifeng125 on the diversity and dynamics of bacterial communities, the accumulation and degradation pattern of the fusion Bt protein in the rhizosphere soil of transgenic maize were detected. Results showed that the contents of Bt protein varied significantly at different developmental stages, but after straw was returned to the field, over 97% of Bt proteins were degraded quickly at the early stages (≤10 d) and then they were degraded at a relatively slow rate. In addition, the variations in bacterial community diversity in the rhizosphere soil were detected by 16S ribosomal RNA (Rrna) high-throughput sequencing technology. A total of 44 phyla, 435 families, and 842 genera were obtained by 16S rRNA sequencing, among which Proteobacteria, Actinobacia, Acidobacter Acidobacterium, and Chloroflexi were the dominant taxa. At the same developmental stage, no significant differences in soil bacterial diversity were detected between Ruifeng125 and its non-transgenic control variety. Further analysis revealed that developmental stage, rather than the transgenic event, made the greatest contribution to the changes in soil microbial diversity. This research provides important information for evaluating the impacts of Bt crops on the soil microbiome and establishes a theoretical foundation for their environmental safety assessment.

Herbicidal proteins from Bacillus wiedmannii isolate ZT selectively inhibit ryegrass (Lolium temulentum L.)

BACKGROUND

The widespread use of chemical herbicides and the growing issue of weed resistance pose significant challenges in agriculture. To address these problems, there is a pressing need to develop biological herbicides based on bacterial metabolites.

RESULTS

In this study, we investigated the impact of the cell-free culture filtrate (CFCF) from the ZT isolate, a bacilliform bacterium obtained from diseased wheat seeds, on the germination and seedling growth of various plant species, including wild oat, ryegrass, redroot, wheat, and chickpea. The results revealed that CFCF had a detrimental effect on the fresh and dry weight of stems and roots in most of the studied plants, except chickpeas. The CFCF was further subjected to separation into aqueous and organic phases using chloroform, followed by the division of the aqueous phase into 13 fractions using an alumina column. Notably, both the aqueous phase (20%) and all 13 fractions (ranging from 50% to 83%) displayed the ability to reduce the root length of ryegrass, a monocotyledonous weed. Liquid chromatography-mass spectrometry (LC-MS) analysis identified that fractions 3 and 7, which were effective against ryegrass but not redroot, contained Cry family proteins, including Cry10 Aa, Cry4 Ba, and Cry4 Aa. Additionally, 16s rRNA gene sequencing revealed that the ZT isolate is closely related (98.27%) to Bacillus wiedmannii.

CONCLUSION

Conclusively, metabolites from the ZT bacterium hold promise for monocotyledonous weed-targeted herbicides, providing a constructive strategy to confront agricultural issues tied to chemical herbicides and weed resistance. © 2024 Society of Chemical Industry.

Impact of Insect-Resistant Transgenic Maize 2A-7 on Diversity and Dynamics of Bacterial Communities in Rhizosphere Soil

Artificial modification of Bacillus thuringiensis (Bt) proteins can effectively improve their resistance to target pests, but the effect of such modification on the diversity of rhizosphere microorganisms remains unclear. Transgenic maize 2A-7 contains two artificially modified Bt proteins, mCry1Ab and mCry2Ab. These proteins can enter soil and pose a potential threat to soil microbial diversity. To assess their impacts on rhizosphere bacteria communities, the contents of the two Bt proteins and changes in bacterial community diversity in the rhizosphere soils of transgenic maize 2A-7 and its control variety were analyzed at different growth stages in 2020. The results showed that the two Bt proteins were detected at low levels in the rhizosphere soils of 2A-7 plants. No significant differences in soil bacterial diversity were detected between 2A-7 and its control variety at any of the growth stages. Bioinformatics analysis indicated that the growth stage, rather than the cultivar, was the main factor causing changes in bacterial communities. This research provides valuable data for understanding the impact of Bt crops on the soil microbiome, and establishes a theoretical basis for evaluation of their safety.

Effects of Insect-Resistant Maize 2A-7 Expressing mCry1Ab and mCry2Ab on the Soil Ecosystem

Transgenic maize 2A-7 expressing mCry1Ab and mCry2Ab has excellent resistance to lepidopteran pests. Previous studies have investigated the effects of several Bacillus thuringiensis (Bt) proteins on the soil. However, the effects of artificially modified Bt proteins on soil ecosystems are still unclear. To evaluate the effects of transgenic maize 2A-7 on soil, the physicochemical properties, enzyme activities and functional diversities of the microbial communities in rhizosphere soils from 2A-7 and its near-isogenic non-transgenic control Dongdan 6531 were analyzed at different developmental stages under field conditions. The alteration of six physicochemical properties (pH, total nitrogen, total phosphorus, organic matter, available phosphorus and alkali-hydrolyzed nitrogen) and six functional enzymes (catalase, alkaline phosphatase, sucrase, acid phosphatase, urease and alkaline protease) activities in the rhizosphere soils between the two maize cultivars were drastically correlated with plant growth stage, but not affected by the artificially modified Bt transgenes. An analysis of time-course Biolog data revealed that the functional diversity of microbial communities in the rhizosphere soil of 2A-7 and its control were similar at each developmental stage. The results suggest that transgenic maize 2A-7 has no significant impact on the soil ecosystem and provide valuable information on scientific safety assessments of 2A-7 and its commercial applications.