A feeling for the micro-organism: structure on a small scale. Biofilms on plant roots

Abstract

Biofilms are structured communities of bacterial cells enclosed in a self-produced polymeric matrix and adherent to an inert or living surface; they have clinical, industrial and environmental impacts. Biofilms that are established by bacteria on plants are found on the surfaces of roots, leaves, seeds and internal vascular tissues where the microbes live in commensal, mutualistic or parasitic/pathogenic associations with their host. The study of the structure of plant-associated biofilms has been considerably helped by the development of techniques using fluorescent markers coupled with confocal scanning laser microscopy as well as scanning electron microscopy. We review several of these techniques as well as some of the research that has dealt with plant-associated biofilms. Our investigations focus on biofilm formation in the early stages of the Rhizobium -legume symbiosis, in which Gram-negative rhizobia provide fixed nitrogen to a host legume, and in return, the legume provides carbon-containing molecules. Because root colonization is an important early step in the establishment of the nitrogen-fixing symbiosis, we looked at Sinorhizobium meliloti attachment and biofilm establishment on the roots of its legume hosts, Medicago sativa L. and Melilotus alba Desr. We also examined biofilm formation by Rhizobium leguminosarum bv. viciae on the roots of Arabidopsis thaliana (L.) Heynh., a non-legume and non-host. Our ultimate goal is to characterize the rhizobial genes involved in aggregation and attachment to roots because several of these appear to be shared in biofilm formation and rhizobial entry of legume root cells.

Effectiveness of exopolysaccharides and biofilm forming plant growth promoting rhizobacteria on salinity tolerance of faba bean (Vicia faba L.)

“…Moreover, increasing the production of exopolysaccharide against higher salt stress leads to support biofilm formation (Ishii et al, 2004;Fujishige et al, 2006). These results are in agreement with those obtained by Arora et al (2010), Qurashi and Sabri (2012), Deng et al (2015) and Kasim et al (2016).…”

Biofilm Formation of Zinc Solubilizing, Potassium Releasing Bacteria on the Surface of Fungi

“…Transmission electron microscopy has shown the presence of fibrillar material around rhizobia attached to the root surface (Fujishige et al, 2006). These observations further support the proposal that root colonizing bacteria are capable of forming biofilms, it is reasonable to suppose that the molecular mechanisms operating in bacterial attachment to roots also might be relevant for biofilm development.…”

Production of exopolysaccharide by Rhizobium leguminosarum bv. trifolii and its role in bacterial attachment and surface properties

“…On the other hand, the results of this study indicated that rhizobial strains Rt24.2(pBA1) and Rt24.2(pBR1), which overproduced EPS had a significantly increased ability to adhere to different surfaces, including soil particles and the host roots, which ensured better survival and adaptation to changing environmental conditions. Similarly in S. meliloti, EPS is required for biofilm development, since an exoY mutant non-producing this polymer forms an immature biofilm (Fujishige et al 2006a;2006b). In this bacterium, a symbiotically active low-molecular-weight fraction of galactoglucan proved to be crucial for biofilm formation and colonisation of host plant roots (Rinaudi and González 2009).…”

“…For this experiment, the method described by Fujishige et al (2006a) was applied with a slight modification. Suspensions of rhizobial strains were made in Fåhraeus liquid medium with OD 600 =0.1.…”

“…The assay of rhizobial cell attachment to quartz sand was performed according to Fujishige et al (2006a;2006b) with some modifications. Briefly, rhizobial strains were grown in 79CA medium containing 1 % glycerol at 28°C for 24 h. For the Rt24.2(pBR1) and Rt24.2(pBA1) strains, kanamycin (20 μg mL −1 ) was added into the medium.…”