INHIBITION OF NITROSOMONAS-EUROPAEA BY MONOTERPENES FROM COASTAL REDWOOD (SEQUOIA SEMPERVIRENS) IN WHOLE-CELL STUDIES

Inhibition by allelochemicals, including monoterpenes, has been sugges ted as a factor in the extremely low nitrification rates observed in c oastal redwood forests. Similarities between the molecular structure o f known nitrification inhibitors and some conifer monoterpenes have be en suggested as one reason for the inhibition of autotrophic nitrifier s by conifer monoterpenes. The effect of monoterpenes on nitrification rate and growth of Nitrosomonas europaea was examined in whole-cell p ure culture experiments using the five most abundant monoterpenes in c oastal redwood needles. These are (in order of decreasing concentratio n in the needles) limonene, alpha-pinene, sabinene, myrcene, and gamma -terpinene. Four of the five compounds significantly inhibited growth of N. europaea in batch culture experiments. Short-term kinetic studie s of the two most inhibitory monoterpenes, limonene and alpha-pinene, were performed on whole cells to evaluate the mode of interaction betw een these chemicals and nitrification rates. Inhibition constants (K-i ) of limonene (38 mu M) and alpha-pinene (95 mu M) were determined. Li neweaver-Burk plots of nitrification in the presence of monoterpenes a ppear to fit a noncompetitive inhibition model; however, the mechanism s of inhibition may be more complex.