Submitted to: American Phytopathological Society Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 3/15/2009
Publication Date: 8/1/2009
Citation: Wallace, P., Mahaffee, W.F., Neill, T.M. 2009. Foliar biofilms of Burkholderia pyrrocinia FP62 on geraniums. American Phytopathological Society Abstracts. p. 568.
Technical Abstract: Biofilm formation on foliar surfaces is commonly associated with plants in water-saturated environments (e.g. tropics or modified environments). On most leaf surfaces bacteria are thought to reside in aggregates with limited production of an exopolysaccharide (EPS) matrix. However, the biocontrol agent, Burkholderia pyrrocinia FP62, was observed to form structures resembling biofilms that covered several leaf cells in the absence of surface water. The development of these biofilms occurred on geranium plants that were inoculated with a suspension of washed FP62 cells and housed in a greenhouse with bottom watering. Leaf samples were examined with both scanning electron microscopy (SEM) and environmental SEM (ESEM) at 0, 1, 3 and 7 days post inoculation. The ESEM was used in conjunction with SEM to identify artifacts associated with the chemical fixation of SEM samples. At Day 0, bacterial cells were randomly distributed on the leaf surface. By Day 1, EPS and other attachment structures were present; aggregates were observed in regions where inoculum collected (e.g. trichomes and cellular junctions). On Day 3, the aggregates are compact and beginning to cover the plant cell surfaces. By Day 7, aggregates had coalesced to cover multiple plant cells. The bacteria were encased in EPS, visible as an opaque layer or as collapsed strands. These observations indicate that bacterial biofilms are able to develop in unsaturated conditions on the surface of geranium leaves.