Interaction between soft rot erwinia and host signals
The purpose of this work was to isolate and characterize host extract-induced mutants of Pectobacterium carotovorum (Pc) affected in their extracellular cell wall degrading enzyme (exoenzyme) production and to identify another class of its inducers. Pectobacterium species cause soft rot disease in a variety of economically important crops in the field and in storage worldwide. Interaction of soft rot bacterial pathogen Pc with its hosts and environment leads to the activation of an array of bacterial genes involved in pathogenicty and virulence of the pathogen. The development of the disease process is not fully understood. The full catalogue of the bacterial virulence genes as well as the host signals which induce them is unknown. A promoterless mini-Tn5 lacZ KmR transposon was used to mutagenize a genetically amenable nalidixic resistant Pc strain KD100 leading to the generation of 26 mutants induced by celery extract and 2 repressed ones. The mutants were altered in their production of exoenzymes compared to the parent. Transposon insertions resulted in six mutants with increased and one with reduced pectate lyase (Pel) production. Five mutants had increased and fourteen had reduced protease (Prt) production. Compared to the parent, four mutants induced by celery extract macerated potato and eleven had reduced capacity to macerate both celery petioles and potato tuber tissues. Products of pectin degradation (Class I inducers) in host extracts are known to induce pectinolytic enzyme production through their interaction with KdgR, a global repressor of exoenzyme production. Using a KdgR - mutant, it was ascertained that, host extracts contains another class of exoenzyme inducers (Class II) different from Class I inducers. The full nature and identity of Class II inducers are unknown except that they are thermostable, water-soluble, diffusible, pH-sensitive and less than 1000 Da in size. Initial purification and GC/MS profiles of the methanol extract of celery petiole for structural identification of the inducer(s) revealed that, the extract contains polar compounds such as ascorbic acid and phenols as well as non-polar compounds such as straight chain aliphatic and cyclic compounds. The results of this work provided and extract that is ready for further studies leading to the identification of the specific inducer of these exoenzymes.
Paul A Agyemang,
"Interaction between soft rot erwinia and host signals"
ETD Collection for Tennessee State University.