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Abstract:
Food security depends on enhancing production and
reducing loss to pests and pathogens. A promising
alternative to agrochemicals is the use of plant
growth-promoting rhizobacteria (PGPR), which are
commonly associated with many, if not all, plant
species. However, exploiting the benefits of PGPRs
requires knowledge of bacterial function and an
in-depth understanding of plant-bacteria associations.
Motility is important for colonization efficiency
and microbial fitness in the plant environment, but the
mechanisms employed by bacteria on and around
plants are not well understood. We describe and
investigate an atypical mode of motility in Pseudomonas
fluorescens SBW25 that was revealed only
after flagellum production was eliminated by deletion
of the master regulator fleQ. Our results suggest that
this ‘spidery spreading’ is a type of surface motility.
Transposon mutagenesis of SBW25ΔfleQ (SBW25Q)
produced mutants, defective in viscosin production,
and surface spreading was also abolished. Genetic
analysis indicated growth-dependency, production
of viscosin, and several potential regulatory and secretory systems involved in the spidery spreading
phenotype. Moreover, viscosin both increases efficiency
of surface spreading over the plant root and
protects germinating seedlings in soil infected with
the plant pathogen Pythium. Thus, viscosin could be
a useful target for biotechnological development of
plant growth promotion agents.
