Increasing survival and efficacy of a bacterial biocontrol agent of fire blight of rosaceous plants by means of osmoadaptation

Abstract

The efficacy of Pseudomonas fluorescens EPS62e in the biocontrol of Erwinia amylovora, the causal agent of fire blight of apple and pear, depends on the colonization of plant surfaces after spray application. A procedure to increase cell survival in the phyllosphere was developed consisting of saline stress and osmolyte amendment to the growth medium during inoculum preparation. Hyperosmotic stress induced the synthesis of the osmolytes trehalose, N-acetylglutaminylglutamine amide and glucosyl-glycerol, but decreasing growth rate. Amendment of the growth medium with glycine betaine increased growth rate and cell yield and promoted its intracellular accumulation. Under controlled environment conditions, osmoadaptation increased by 10- to 100-fold cell survival to desiccation and to low relative humidity conditions on plant surfaces, in comparison with the nonosmoadapted controls. In the field, cell survival increased 100-1000 times in immature fruit upon osmoadaptation but was not significantly affected in flowers where active colonization occurs. The efficacy in the control of fire blight infections was increased 30-50% upon osmoadaptation on immature fruits but was not affected in blossoms. The method of osmoadaptation may be useful for improving the fitness and efficacy of biological control agents of phyllosphere pathogens under limiting humidity conditions.

Room temperature stabilization of oral, live attenuated Salmonella enterica serovar Typhi-vectored vaccines

“…Several groups have suggested that growth and harvesting conditions also have a significant effect on the physical stability of bacteria [55–58]. Sodium chloride at various concentrations was incorporated in BHI broth to determine its effect on both the growth kinetics of Ty21a as well as its development of resistance to osmotic stress.…”

Trehalose: Current Use and Future Applications

“…For example, Pseudomonas fluorescens EPS62e that contained higher levels of intracellular trehalose, as a response to salt stress, demonstrated higher desiccation tolerance. 266 Leslie et al 97 utilized trehalose (100 mM) to stabilize both Escherichia coli (E. coli) DH5" and Bacillus thuringiensis (B. thuringiensis) HD-1 by freeze drying. In the absence of any protectants, only 8% of E. coli and 14% of B. thuringiensis survived, whereas in the presence of 100 mM trehalose, the survival rate increased to 70% and 57%, respectively.…”

Improvement of Fitness and Efficacy of a Fire Blight Biocontrol Agent via Nutritional Enhancement Combined with Osmoadaptation

“…P. fluorescens EPS62e was cultured, for routine use, in Luria-Bertani (LB) broth to obtain standard cells or in glucose minimal medium (GMM) plus NaCl and glycine betaine (GB) to obtain osmoadapted cells as previously described (4). To monitor culturable populations of EPS62e in the field, a spontaneous mutant resistant to nalidixic acid (EPS62e Nal r ) was selected on LB agar supplemented with 50 mg liter Ϫ1 of nalidixic acid.…”

“…A procedure of osmoadaptation based on the combination of saline osmotic stress and osmolyte amendment of the growth medium has been used to increase drought stress tolerance and improve epiphytic survival and biocontrol efficacy of the apple blue mold biocontrol agent Pantoea agglomerans EPS125 (3) and the fire blight biocontrol agent P. fluorescens EPS62e (4).…”