Scanning Electron Microscopy for characterization of Bradyrhizobium diazoefficiens USDA 110 on solid substrate

ADRIANA GABRIELA LÓPEZ GUERRA; ANÍBAL ROBERTO LODEIRO; MARIA JULIA ALTHABEGOITI

La Plata

Workshop; Imaging Techniques for Biotechnology and Biomedical Applications; 2016

Universidad de La Plata

Bradyrhizobium diazzoefficiens is a rhizobia capable of establishing a symbiotic relationship with soybean (Glycine max), which induces the formation of root nodules where occurs biological nitrogen fixation. Often applied as inoculant in soybean crops, this Gram negative bacillus presents different lifestyles. B. diazoefficiens is able to live in the soil for long periods of time, either forming biofilms as in planktonic state.As a saprophyte soil bacterium is not able to fix nitrogen, but it can consume various carbon sources and persist long periods of time. In this state (planktonic) it can move through flagella and chemotactically respond to various substances as exuded by the roots to the rhizosphere (Caetano-Anollés et al. 1988, Barbour et al. 1991, Chuiko et al., 2002, Brencic & Winans 2005). B diazoefficiens USDA 110 has two systems flagella involved in mobility on liquid media (swimming) and on surfaces (swarmming) (Althabegoiti et al, 2008;. 2011; Covelli et al, 2013;. Kanbe et al, 2007).It is proposed that the rhizobia swim in the solution contained in the pores of the soil to the roots approach and initiate adhesion and infection. However, many of the experiments to support this have been carried out in liquid media, which represents an extremely simplified experimental system to extrapolate conclusions to what actually happens on the ground.Alternatively the planktonic state, B. diazoefficiens could establish biofilms on various surfaces. Biofilms are defined as communities or sessile bacterial lacking flagella, where cells are embedded in a matrix of extracellular polymeric components adhered to a biotic or abiotic substrate (Branda et al., 2005). The ability to form biofilms not seem restricted to any specific group of microorganisms and it is considered that under ambient appropriate conditions the majority of bacteria can form biofilms on surfaces to resist unfavorable environmental conditions such as antibiotics, ultraviolet light, desiccation and predators (Stoodley et al., 2002). However, the processes involved in the formation signaling pathways and regulatory mechanisms of biofilms are unknown. In many bacterial species, the production of a biofilm is affected by surface and extracellular components (mainly flagella and exopolysaccharides), along with environmental and quorum sensing signals. Soil can be considered one of the most complex and diverse ecosystems. Because of its heterogeneity, the densities of the microbial population can vary up to three orders of magnitude. It is necessary to develop a systems more similar to ground conditions that a liquid medium. Is currently unknown how rhizobial mobility occurs in the soil and how it relates to the radical colonization and nodulation. While studies in liquid medium allowed to have a first approach to microbial behavior, far from what happens in nature, where there is a marked influence of the environment on the position and distribution of bacterial populations (Lopez Garcia et al., 2002) as well as in the state they are in and the relationships established between themselves and with other species in its ecological niche.Scanning electron microscopy (SEM) is useful tool to visualize the external appearance of bacteria and is an important first approach to produce knowledge about what happens under natural conditions. Through this tool we were able to visualize the adhesion of bacteria under culture conditions, as well as a possible formation of biofilm.