Effects of stressful physico-chemical factors on the fitness of the plant pathogenic bacterium Dickeya solani

Abstract

Dickeya solani is a pectinolytic bacterium that causes significant losses of potato crops. Interaction between bacteria and plant during infection and transmission within the host tissue are associated with a variety of challenges, including exposure to physico-chemical factors that induce osmotic, acidic, oxidative or thermal stresses. In this work, we tested the effects of various potentially adverse conditions on growth and fitness of the D. solani IPO2222 type strain. We found the bacteria were able to withstand a great variety of stressful conditions. Treatment with high concentrations of osmolytes (up to 1.6 Osm), low pH (5.0), or elevated temperature (up to 40 °C) was still tolerated. Short term exposure to these conditions did not impair the ability of bacteria to macerate potato tuber tissue. However, D. solani was sensitive to a relatively low content (above 0.5 mM) of the oxidant H2O2 and treatment with this oxidant caused a loss of culturability. All used stressful conditions are known to affect the stability, and structure of proteins and induction of the folding stress-related genes, dnaK, dnaJ and groEL, was observed in most cases. The only exception was oxidative stress for which the chaperone genes were slightly down-regulated. This observation is in line with a low tolerance of D. solani to H2O2.