Abstract
The genus Flavobacterium is characterized by the capacity to metabolize complex organic compounds and a unique gliding motility mechanism. Flavobacteria are often abundant in root microbiomes of various plants, but the factors contributing to this high abundance are currently unknown. In this study, we evaluated the effect of various plant-associated poly- and mono-saccharides on colony expansion of two Flavobacterium strains. Both strains were able to spread on pectin and other polysaccharides such as microcrystalline cellulose. However, only pectin (but not pectin monomers), a component of plant cell walls, enhanced colony expansion on solid surfaces in a dose- and substrate-dependent manner. On pectin, flavobacteria exhibited bi-phasic motility, with an initial phase of rapid expansion, followed by growth within the colonized area. Proteomic and gene expression analyses revealed significant induction of carbohydrate metabolism related proteins when flavobacteria were grown on pectin, including selected SusC/D, TonB-dependent glycan transport operons. Our results show a positive correlation between colony expansion and the upregulation of proteins involved in sugar uptake, suggesting an unknown linkage between specific operons encoding for glycan uptake and metabolism and flavobacterial expansion. Furthermore, within the context of flavobacterial-plant interactions, they suggest that pectin may facilitate flavobacterial expansion on plant surfaces in addition to serving as an essential carbon source.
Highlights
The complex interactions between plant-associated microorganisms and their hosts are crucial for plant health and growth (Berendsen et al, 2012; Bulgarelli et al, 2013; Reinhold-Hurek et al, 2015)
We found that pectin, a prominent plant cell wall polysaccharide, facilitates expansion of flavobacteria on solid surfaces, even in the presence of nutrient-rich media
We postulate that pectin may enhance the capacity of flavobacteria to efficiently colonize and proliferate on plant surfaces
Summary
The complex interactions between plant-associated microorganisms and their hosts (collectively referred to as the “plant holobiont”) are crucial for plant health and growth (Berendsen et al, 2012; Bulgarelli et al, 2013; Reinhold-Hurek et al, 2015) Plants modulate their rhizospheres, by exuding various small molecular weight compounds (rhizodeposits) such as sugars, amino acids, and organic acids, by rhizodepositing root cap border cells, and by releasing various monoand polysaccharides in their mucilage (Dennis et al, 2010; Barret et al, 2011; Beauregard et al, 2013; Reinhold-Hurek et al, 2015; Massalha et al, 2017; Sasse et al, 2018). Root recruitment and colonization mechanisms of certain plant-growth-promoting rhizobacteria (PGPR) have been identified and characterized (Lugtenberg and Dekkers, 1999; Yan et al, 2008; Pieterse et al, 2014), those responsible for recruitment of the vast majority of rhizoplane bacteria are currently an enigma
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