title: Evidence that caterpillar labial saliva suppresses infectivity of potential bacterial pathogens.
abstract: Salivary enzyme, glucose oxidase (GOX) from the caterpillar Helicoverpa zea, catalyzes the conversion of glucose to gluconic acid and hydrogen peroxide. Because hydrogen peroxide has well-known antimicrobial properties, we examined whether caterpillar labial saliva could reduce the infectivity of bacterial pathogens. We examined the effects of caterpillar saliva on the growth of two bacteria species Serratia marcescens and Pseudomonas aeruginosa. Wells formed in LB agar contained a solution of salivary gland extract (Sx) and glucose, GOX and glucose, Sx only, GOX only, or glucose only. After 18 h of incubation, the diameter of cleared bacteria was measured. Wells treated with only GOX, Sx, or glucose showed no measurable area of clearing, while wells treated with GOX with glucose or Sx with glucose had considerable clearing. To determine if saliva could provide protection to caterpillars in vivo, a surgery was performed on caterpillars that prevented the secretion of labial saliva. Caterpillars were fed a diet containing either no added bacteria or treated with high levels of S. marcescens or P. aeruginosa. Caterpillars that could not secrete saliva had significantly higher levels of mortality when feeding on diet treated with either bacterium than caterpillars that could secrete saliva when feeding on equal levels of bacteria-treated diet. Our evidence demonstrates for the first time that insect saliva in situ can provide protection against bacterial pathogens and that the salivary enzyme GOX appears to provide the antimicrobial properties.
authors.affiliation: Department of Biological Sciences, Western Illinois University, Macomb, Illinois 61455, USA. ro-musser@wiu.edu
authors.forename: Richard O
authors.initials: RO
authors.lastname: Musser
authors.forename: Hyeog S
authors.initials: HS
authors.lastname: Kwon
authors.forename: Spencer A
authors.initials: SA
authors.lastname: Williams
authors.forename: C James
authors.initials: CJ
authors.lastname: White
authors.forename: Michael A
authors.initials: MA
authors.lastname: Romano
authors.forename: Scott M
authors.initials: SM
authors.lastname: Holt
authors.forename: Shay
authors.initials: S
authors.lastname: Bradbury
authors.forename: Judith K
authors.initials: JK
authors.lastname: Brown
authors.forename: Gary W
authors.initials: GW
authors.lastname: Felton
mesh_terms: D000818:Animals; D000890:Anti-Infective Agents / Q000494:pharmacology; D001419:Bacteria / Q000187:drug effects / Q000302:isolation & purification / Q000472:pathogenicity*; D007700:Kinetics; D007915:Lepidoptera / Q000382:microbiology / Q000502:physiology*; D012463:Saliva / Q000382:microbiology / Q000502:physiology*; D014020:Tissue Extracts / Q000302:isolation & purification / Q000494:pharmacology
chemical_list: D000890:Anti-Infective Agents; D014020:Tissue Extracts