|ORLANDI, E - UNIVERSITY OF MD
|ANDERSON, A - UTAH STATE UNIVERSITY
Submitted to: Physiological and Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/11/1997
Publication Date: N/A
Interpretive Summary: There has been a great deal of debate in recent years concerning the role that active oxygen species play in plant/pathogen interactions. Because active oxygen species such as H202 are anti-bacterial H202 produced during plant/bacteria interactions could limit the development of bacterial diseases. However, bacterial pathogens possess catalase, an enzyme capable of quickly degrading high concentrations of H202. This study examined the relationship between H202 and the bacterial survival and the effect on this relationship of 1) bacterial concentration; 2) H202 concentration; 3) H202-scavenging activity. It also examined the effect of bacterial concentration on H202 accumulation during plant/pathogen interactions. This study is important in that it defines a limited role for catalase in bacterial survival that contradicts earlier studies on bacterial survival and pathogenesis. This manuscript will be useful to microbiologists and plant pathologists who are interested plant/pathogen interactions.
Technical Abstract: In vitro studies with Pseudomonas sp. characterized the relationship between H2O2-scavenging and culturability of bacteria. Scavenging activity and survival of bacteria were proportionally related to bacterial concentration at H202 concentrations above that which an individual cell could tolerate. The rate of H202-scavenging by a bacterial population increased with H202 concentration. This was probably due to bacterial catalases,, which are known to have a high Km. Studies with a catalase-deficient mutant of P. putida, however, indicated that bacterial catalase had little effect on scavenging external H202 at the lower concentrations of H202 that are like to be encountered in suspension cells and other plant tissues. Bacterial catalase also had little effect on the accumulation of H202 in suspension cells treated with various isolates of Pseudomonas sp. H202 accumulation in treated suspension cells was affected by bacterial concentration, however, indicating the presence of a non-catalatic H202 scavenger. Catalase also appeared to be unimportant in determining the culturability of low inoculum concentrations of P. putida after exposure to H202.