Root exudates as regulators of plant colonization by Methylobacterium spp. and Methylorubrum extorquens.

Author(s)

Maria Alejandra Mantilla Galindo

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Ciências Biomédicas (ICB/SDI)
• Defense date: 2019-12-09

Examining board members

Gabriel Padilla Maldonado; Galdino Andrade Filho; Andrea Balan Fernandes; Rodrigo Gouvêa Taketani

• Advisor: Welington Luiz de Araujo

Abstract

The genus Methylobacterium can establish epiphytic or endophytic associations with different plant species. For the establishment of interaction, chemical communication between plant and bacteria take place, in this communication the root exudates probably play a key role. Previous studies showed that the strain M. mesophilicum SR1.6/6 increased their development in root exudates and the expression of colonization related genes (catalytic activity, biofilm formation, primary metabolism and antioxidant genes). However, the importance and functions of plant root exudates during interaction with Methylobacterium are not well understood. Therefore, this work aims to determinate the role of soybean (Glycine max) and corn (Zea mays) seedling root exudates in the establishment of interaction with Methylobacterium spp. and Methylorubrum extorquens. Thus, specific primers were designed for three Methylobacterium spp. strains and one Methylorubrum extorquens strain. These primers were used for the strains quantification in soil and seedlings roots (soybean and corn) by qPCR. Additionally, the composition of seedlings roots in interaction with Methylobacterium were identified by GC-MS and the influence of exudates in biofilm formation were evaluated. Thus, it was observed that the strains AR1.6/2 (M. extorquens) and MP2-3 (M. hispanicum) when inoculated individually survived in the soil for up to 90 days, while the strains SR1.6/6 (M. mesophilicum) and R16E (M. fujisawaense) showed a low survival. In bacterial consortia, only MP2-3 strain was survived for 90 days in soil. In the interaction experiments was evidenced that SR1.6/6 strain when inoculated individually had the biggest abundance in soybean roots but in consortia had the lowest. In corn root, the abundance of bacteria didnt differ significantly. From GC-MS analyzes, was observed that soybean and corn seedlings presented different profiles, and corn seedlings showed a higher percentage of carbohydrates (16%) and organic acids (7%), in comparison with soybean, which presented 14% of carbohydrates and 2% of organic acids. During interaction, carbohydrates, organic acids and amino acids percentages increased in soybean and corn seedlings. Finally, it was evidenced that corn seedling exudates induced the bacterial biofilm formation. The results obtained in this work show the influence of exudates in the selection of specific strains of Methylobacterium and or Methylorubrum, by providing specific carbon sources, and its suggested that the success of plant colonization by Methylobacterium is dependent on the metabolism of these nutrient sources. (AU)

• FAPESP's process: 17/03422-4 - Influence of plant exudates on the ecology of Methylobacterium spp. during interaction with the host plant
• Grantee: Maria Alejandra Mantilla Galindo
• Support Opportunities: Scholarships in Brazil - Master