Effects of Six-Carbon Aldehydes and Alcohols on Bacterial Proliferation

Lipoxygenase/hydroperoxide lyase generated compounds are thought to be important in plant defense. The effects of volatile compounds from this pathway on the proliferation of Escherichia coli TBI, Pseudomonas syringae pv. tabaci, and Pseudomonas syringae pv. angulata were evaluated. The vaporphase concentrations of compounds in the bioassay system were estimated by gas chromatography. At the highest concentrations tested, the C₆ aldehyde (E)-2-hexenal completely inhibited proliferation of both P. syringae pathovars (570 µg/L of air) and E. coli (930 µg/L of air). Similarly, the C₆ alcohol (E)-2-hexen-1-ol prevented proliferation of P. syringae pathovars (1100 µg/L of air) and E. coli (2300 µg/L of air). Among the bacteria tested, one isolate of P. syringae pv. angulata was the most sensitive to a lipoxygenase pathway volatile, exhibiting decreased proliferation after exposure to (E)-2-hexenal (40 µg/L of air). The unsaturated volatiles, (E)-2-hexenal and (E)-2-hexen-1-ol, exhibited a greater inhibitory effect than the saturated volatiles, hexanal and 1-hexanol. The responses to the volatile compounds observed for E. coli TBI and P. syringae pv. tabaci were similar and differed somewhat from that of P. syringae pv. angulata.