Fig. 5

Effect of internal compatible solute composition on heat resistance of conidia. Measurements were performed in biological triplicates. a, Internal compatible solute composition of conidia from knock-out strains determined by HPLC analysis. Conidia from the ΔmpdA, ΔtpsABC strain contained no measurable trehalose and very little mannitol (significantly different from wild type p < 0.05 tested with Student’s t-test). The four-fold and five-fold knock-out strains were complemented back to wild type by reintroducing the genes containing two silent point mutations at the original loci. These strains show a restored compatible solute composition and conidial heat resistance comparable to wild type conidia. The five-fold knock-out strain with only the mtdB gene restored, re-introduces the low compatible solute composition profile. b, Survival plates showing CFUs of conidia from compatible solute mutants after heat treatment. Zero colonies were found testing the conidia of a ΔmpdA, ΔtpsABC strain after a relatively mild heat stress of 55 °C was applied, correlating with absent trehalose and a low mannitol concentration. c, Heat inactivation curves of conidia from compatible solute knock-out strains. Conidia of these strains were subjected to heat stress in a heat bath at 54 °C and sampled for up to 60 min. Mean values of three biological replicates are shown; standard deviations are indicated by error bars. D-values were calculated based on linear regression (Table 1)