Comparison of methionine metabolism in symbiotic and aposymbiotic larvae of Sitophilus oryzae L. (Coleoptera: Curculionidae)—II. involvement of the symbiotic bacteria in the oxidation of methionine

Abstract

1. 1. Mcthionine metabolism was investigated in symbiotic and aposymbiotic larvae of Sitophilus oryzae. Nutritional experiments involving methionine and ethionine (an antagonist of methionine) indicated that the symbiotic larvae had a better ability to oxidize the sulphur atom of these two amino acids than did the aposymbiotic larvae. 2. 2. Enzymatic experiments with larval bacteriomes showed that the symbiont-containing bacteriocytes were directly involved in this oxidation. 3. 3. It is therefore demonstrated that methionine metabolism differ in the presence and in the absence of the symbiotic bacteria and that the high level of methionine sulfoxide observed in the symbiotic larvae could be an adaptative response to diets high in methionine, as it has been shown for sarcosine in the aposymbiotic larvae.