Biological aspects of plant growth promotion by Bacillus thuringiensis RZ2MS9 with focus on phosphate fertilization

Author(s)

Bruna de Moura Lopes

• Document type: Master's Dissertation
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2023-03-22

Examining board members

Maria Carolina Quecine Verdi; Paulo Teixeira Lacava; Paulo Sergio Pavinato

• Advisor: Maria Carolina Quecine Verdi

Abstract

Phosphorus (P) is an essential macronutrient for good plant growth and development. Due to the characteristics of Brazilian soils, the application of high doses of phosphate fertilizers cannot meet the need for this element during the plant cycle. Aiming at greater productivity and sustainability, alternative strategies are needed for the use and better use of P present in the soil. For this, the use of plant growth promoting rhizobacteria (PGPR), mainly P solubilizing bacteria (PSB), are strategies to be implemented in order to reduce the use of traditional fertilizers. Among these bacteria, the genus Bacillus has been shown to be a good growth promoter for commercially relevant plants. Bacillus thuringiensis (Bt) RZ2MS9 is a rhizobacterium previously isolated from the guarana root capable of promoting the growth of corn, soybeans and tomatoes, but until now it had not been tested on sugarcane, an economically important crop for Brazil. The complete genome sequencing of this lineage allowed the search for genes of agronomic interest. Based on this, the Bt RZ2MS9 strain was evaluated for its ability to promote growth in three sugarcane varieties. The strain was able to increase the sprouting rate, height and dry weight of shoots and amount of chlorophyll A and B. However, although the colonization rate of the leaves were statistically equal, the ability to promote growth from inoculation was different among sugarcane varieties. Subsequently, the strain was tested for growth promotion and P accumulation in corn, sugarcane and soybean inoculated in P-rich soil and compared to the commercial product Biomaphos® and control without inoculant. In this experiment, greater phosphatase activity was observed in soils inoculated with Bt RZ2MS9 and Biomaphos® regardless of the evaluated crop. There was no growth promotion by the evaluated parameters and the accumulation of leaf P was statistically higher at the end of the experiment with corn in the control treatment. In parallel, a modulation in the expression of genes related to the PhoP/PhoR two-component system (TCS) was observed via RT-qPCR under different concentrations of soluble P. In medium with low P concentration, the phoP gene was downregulated after six hours of inoculation. After 24 hours, genes related to alkaline phosphatase and cell wall modification were upregulated. In medium with high P concentration, the phoP gene was downregulated, and the pstS, tuaE and tuaG genes were upregulated. Finally, a knockout process via CRISPR-Cas9 of the phoP and phoR genes that code for the main proteins of the TCS under study was started. (AU)

• FAPESP's process: 20/10149-5 - PhoPR system of Bacillus sp. RZ2MS9 and its response to phosphate fertilization in corn
• Grantee: Bruna de Moura Lopes
• Support Opportunities: Scholarships in Brazil - Master