ISHS Acta Horticulturae 217: IV International Workshop on Fire Blight
POSSIBLE DETERMINANTS OF PATHOGENICITY OF ERWINIA AMYLOVORA ; EVIDENCE FOR AN INDUCED TOXIN |
| Authors: | D. Youle, R.M. Cooper |
| Abstract:
Attempts are being made to isolate the causal factor(s), of bacterial or host origin, of increased cell permeability in infected host tissues. Host cell electrolyte leakage and viability was assessed using immature pear fruit discs or suspension cultured apple cells. Virulent bacteria grown in the presence or absence of host tissues lost their capacity to induce cell leakage when killed by heat or streptomycin. The potentially toxic endo-polygalacturonidases are not produced by E. amylovora EPS produced during growth on artificial media or with host tissue failed to induce electrolyte leakage; cell-free fluids from liquid cultures were also ineffective. However, sterile filtrates from the interaction between host tissue and either a virulent capsulated isolate (T) or an avirulent, non-capsulated mutant capable of inducing cell leakage (E8) (but not from the capsulated avirulent isolate P) possessed toxic activity when concentrated 35-fold. Toxicity from culture salts was circumvented by performing the host-parasite interaction in deionised water. Division of concentrated fluids into high and low molecular weight fractions showed that only the latter was active. Ultrafiltration indicates the size of the 'toxin' is 1000 daltons. This is consistent with the need for any leakage-inducing agent to pass from intercellular spaces through the molecular sieve of the host cell wall matrix. Characterisation and origin of the putative induced toxin are currently under investigation. | |
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