Biofilm formation and maize root-colonization of seed-endophytic Bacilli isolated from native maize landraces

Abstract

Agricultural microbiology seeks to replace the use of agrochemicals with microbe-based products. Plant growth-promoting bacteria (PGPB) are often selected based on their functions in vitro, and then, their effect on plant development is tested. However, this approach neglects the study of their survival in soil, root-colonization, and the monitoring of beneficial functions in the rhizosphere. This could explain the recurrent lack of success in the transition from lab tests to field applications of natural isolates from novel habitats. In our recent studies, we found that native maize seeds from traditional agroecosystems carry endophytic bacterial communities that are dominated by members of the class Bacilli. As an approach to grasp their PGP potential, we developed protocols to test maize root-colonization of these natural isolates in 1) a short-term hydroponics assay in vitro and 2) a long-term assay in non-sterile soil pots. Our results show that in vitro biofilm formation was only partially associated to short-term colonization in vitro; furthermore, long-term root-colonization in soil pots was not correlated to the in vitro assays. This work highlights the necessity to incorporate root-colonization assays as part of the research strategies in the search for PGPB natural isolates from unexplored habitats, towards the generation of inoculants with increased success in the field.