Lysosomes and sulfide-oxidizing bodies in the bacteriocytes of Lucina pectinata, a cytochemical and microanalysis approach
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Lucina pectinata is a large tropical clam living deeply burrowed in the black, reducing mud of mangrove swamps. It is known to possess hemoglobin in the cytoplasmic areas of its bacteriocytes, which harbor sulfide-oxidizing bacteria. The bacteriocytes also possess lysosome-like microbodies containing either membrane whorls or electron-dense granules in which free heme compounds have been identified. The cytochemical detection of acid phosphatase and arylsulphatase through EDX (energy-dispersive X-ray) microanalysis strongly suggests that the bacteriocytes of L. pectinata contain, in fact, two different types of microbodies. Some of these (devoid of dense granules) possess a variable amount of lysosomal enzymes and occasionally a limited quantity of iron, which may result from a recycling process of hemoglobin. Their main function seems to be the digestion of a limited proportion of symbiotic bacteria. They represent genuine secondary lysosomes with a functionally acidic pH. The second type of microbodies is characterized by dense granules containing sulfur and iron hemes but no lysosomal enzymes. Their sulfide-oxidizing activity was substantiated by benzyl viologen assay, with Na2S as a substrate. These microbodies appear to be similar to the sulfide-oxidizing 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, characterized by a functionally basic pH and pseudoperoxidasic activity, and have been termed SOBs. Therefore, the bacteriocytes of L. pectinata possess at the same time functional lysosomes and functional SOBs.
KeywordsBivalve Acid Phosphatase Lysosomal Enzyme Iron Heme Dense Granule
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