COLONIZATION PATTERNS OF THE N2-FIXING BACTERIA Burkholderia tropica IN BARLEY

GARCÍA, SABRINA; BERNABEAU P; BOIARDI J L; LUNA M. F.

Córdoba

Congreso; XI CONGRESO ARGENTINO DE MICROBIOLOGÍA GENERAL SAMIGE; 2015

Sociedad Argentina de Microbiología General

The use of biofertilizerand biocontrol organisms is being considered as an alternative or asupplementary way of reducing the use of chemicals in agriculture. Plant growthpromoting bacteria (PGPB) are a group of microorganisms able to conferbeneficial effects on plant growth and development, without causing damageneither to the host nor the environment. These microorganisms stimulate plantgrowth as a consequence of nitrogen fixation, production of phytohormones,enhancement of mineral availability and biocontrol of phytopathogens.PGPB haveto colonize and grow on or around the roots for the establishment of aneffective plant-microbe interaction. After this necessary step, some of themare able to enter roots by different mechanisms and establish endophytic populations.The study of colonization process and patterns will give a more detailedinsight into plant bacterial interactions and is a critical prerequisite forthe development of effective inoculants.Several diazotrophic plant-associatedBurkholderia species have been described as promising candidates forbiotechnological applications. In order to find PGPB for grasses, the aim ofthis work is to characterize the colonization pattern of the N2-fixing bacteriaB. tropica MTo-293 containing the marker gene Green Fluorescent Protein whenbarley seeds are inoculated with this bacterium and grown under gnotobioticconditions. Colonization was monitored by plating bacterial suspensions fromhomogenized tissues (CFU/g fresh weight) and by microscopic localization of bacteria.B.tropica could be isolated from root surfaces (up to 12 log CFU/g fresh weight),from surface-disinfected and disrupted roots (4.0 log CFU/g fresh weight) andalso from stems of inoculated barley plants. Microscopic assays showed a wideroot surface colonization by B. tropica in these plants. This is in accordancewith the high rhizoplane population densities found in all plants tested thatare higher compared to B. tropica surface populations in other inoculatedgrasses. Microscopic studies showed colonizing bacteria on root hairs, lateralroot emergence sites and root surfaces.These results show that inoculation ofbarley seeds with B. tropica led to an extensive root colonization of barleyplants. Moreover, it is able to colonize other plants than its original hostand also establish stable associations, at least under our experimentalconditions.