The key role of indole-3-acetic acid biosynthesis by Bacillus thuringiensis RZ2MS9 in promoting maize growth revealed by the ipdC gene knockout mediated by the CRISPR-Cas9 system.

The bacterial biosynthesis of indole-3-acetic acid (IAA) is often related to the beneficial effects of plant growth-promoting rhizobacteria (PGPR) on plant development. In PGPR belonging to the Bacillus genus, the synthesis of IAA may occur through different metabolic pathways that are still poorly understood. B. thuringiensis (Bt) is well known for its insecticidal properties; however, its beneficial features are not limited to pest control. Our group has been studed the beneficial effects of Bt strain RZ2MS9 as growth promoter in a range of plant crops, including soybean, tomato, and maize. We recently demonstrated that bacterial IAA biosynthesis plays an important role in the ability of RZ2MS9 to benefit plant development. However, the molecular involved mechanisms in the IAA biosynthesis by this bacterium in the beneficial interaction with plants remain unclear. Here, we investigated the genetic basis of IAA biosynthesis by RZ2MS9. We knocked out the ipdC gene, involved in IAA biosynthesis via the tryptophan-dependent IPyA pathway, using the CRISPR-Cas9 system. Our results showed that, by disrupting the IPyA pathway, the amount of IAA synthesized by the mutant RZ2MS9 (ΔipdC) in the presence of tryptophan drops 57%. The gene knockout did not affect the bacterial growth, but it did affect its ability to colonize maize. Moreover, deactivating the ipdC gene in RZ2MS9 significantly reduces its ability to promote maize growth. ΔipdC performed worse than RZ2MS9 in almost all evaluated plant parameters, including total root length, projected root area, lateral roots, aerial part dry matter, and germination speed index. Therefore, we demonstrated that tryptophan-dependent IAA biosynthesis via the IPyA pathway by RZ2MS9 is strongly influenced by the ipdC gene. Furthermore, IAA biosynthesis by RZ2MS9 is a major mechanism used by this PGPR to promote maize growth.

Mangrove endophyte promotes reforestation tree (Acacia polyphylla) growth

ABSTRACT Mangroves are ecosystems located in the transition zone between land and sea that serve as a potential source of biotechnological resources. Brazil's extensive coast contains one of the largest mangrove forests in the world (encompassing an area of 25,000 km2 along all the coast). Endophytic bacteria were isolated from the following three plant species: Rhizophora mangle, Laguncularia racemosa and Avicennia nitida. A large number of these isolates, 115 in total, were evaluated for their ability to fix nitrogen and solubilize phosphorous. Bacteria that tested positive for both of these tests were examined further to determine their level of indole acetic acid production. Two strains with high indole acetic acid production were selected for use as inoculants for reforestation trees, and then the growth of the plants was evaluated under field conditions. The bacterium Pseudomonas fluorescens (strain MCR1.10) had a low phosphorus solubilization index, while this index was higher in the other strain used, Enterobacter sp. (strain MCR1.48). We used the reforestation tree Acacia polyphylla. The results indicate that inoculation with the MCR1.48 endophyte increases Acacia polyphylla shoot dry mass, demonstrating that this strain effectively promotes the plant's growth and fitness, which can be used in the seedling production of this tree. Therefore, we successfully screened the biotechnological potential of endophyte isolates from mangrove, with a focus on plant growth promotion, and selected a strain able to provide limited nutrients and hormones for in plant growth.

Mangrove endophyte promotes reforestation tree (Acacia polyphylla) growth.

Mangroves are ecosystems located in the transition zone between land and sea that serve as a potential source of biotechnological resources. Brazil's extensive coast contains one of the largest mangrove forests in the world (encompassing an area of 25,000km2 along all the coast). Endophytic bacteria were isolated from the following three plant species: Rhizophora mangle, Laguncularia racemosa and Avicennia nitida. A large number of these isolates, 115 in total, were evaluated for their ability to fix nitrogen and solubilize phosphorous. Bacteria that tested positive for both of these tests were examined further to determine their level of indole acetic acid production. Two strains with high indole acetic acid production were selected for use as inoculants for reforestation trees, and then the growth of the plants was evaluated under field conditions. The bacterium Pseudomonas fluorescens (strain MCR1.10) had a low phosphorus solubilization index, while this index was higher in the other strain used, Enterobacter sp. (strain MCR1.48). We used the reforestation tree Acacia polyphylla. The results indicate that inoculation with the MCR1.48 endophyte increases Acacia polyphylla shoot dry mass, demonstrating that this strain effectively promotes the plant's growth and fitness, which can be used in the seedling production of this tree. Therefore, we successfully screened the biotechnological potential of endophyte isolates from mangrove, with a focus on plant growth promotion, and selected a strain able to provide limited nutrients and hormones for in plant growth.