Lysosomes and sulfide-oxidizing bodies in the bacteriocytes of Lucina pectinata, a cytochemical and microanalysis approach

Lucina pectinata is a large tropical clam living deeply burrowed in the bla ck, reducing mud of mangrove swamps. It is known to possess hemoglobin in t he cytoplasmic areas of its bacteriocytes, which harbor sulfide-oxidizing b acteria. The bacteriocytes also possess lysosome-like microbodies containin g either membrane whorls or electron-dense granules in which free heme comp ounds have been identified. The cytochemical detection of acid phosphatase and arylsulphatase through EDX (energy-dispersive X-ray) microanalysis stro ngly suggests that the bacteriocytes of L. pectinata contain, in fact, two different types of microbodies. Some of these (devoid of dense granules) po ssess a variable amount of lysosomal enzymes and occasionally a limited qua ntity of iron, which may result from a recycling process of hemoglobin. The ir main function seems to be the digestion of a limited proportion of symbi otic bacteria. They represent genuine secondary lysosomes with a functional ly acidic pH. The second type of microbodies is characterized by dense gran ules containing sulfur and iron hemes but no lysosomal enzymes. Their sulfi de-oxidizing activity was substantiated by benzyl viologen assay, with Na2S as a substrate. These microbodies appear to be similar to the sulfide-oxid izing bodies (SOBs) described in the bacteriocytes of other bivalve species with symbiotic thioautotrophic bacteria; however, their sulfide-oxidizing activity appears to be non-enzymatic. They are discrete organelles, charact erized by a functionally basic pH and pseudoperoxidasic activity, and have been termed SOBs. Therefore, the bacteriocytes of L. pectinata possess at t he same time functional lysosomes and functional SOBs.