MARTIN, Gary G.; Occidental College, Los Angeles: The peritrophic membrane of the ridgeback prawn, Sicyonia ingentis

Peritrophic membranes (PTM) are acellular layers that separate ingested food from the gut epithelium and persist as wrappers of fecal pellets. Although found in several protostomes, they are most thoroughly studied in insects, and to a lesser extent other arthropods. Most PTM contain chitin fibers embedded in a matrix of proteins, glycoproteins, and proteoglycans. The purpose of this study is to describe the structure, composition, formation, and permeability of the PTM in a penaeid shrimp with particular interest in its potential as a barrier to ingested pathogens. The PTM in S. ingentis are produced by columnar cells with an apical brush border. The apical cytoplasm is filled with granules that show a cycle of formation, hydration and secretion. The granules do not bind the lectin WGA which is specific for N-acetyl-D-glucoasmine the basic monomer of chitin. The function of the secreted granules is unknown and requires further investigation. WGA does bind to the sides and tips of the microvilli. This indicates that chitin production occurs between the microvilli, where presumably the other components are also added. TEM of intact PTM show a grid pattern with spacing matching the packing of microvilli. It has been suggested that the microvilli serve as a template for the formation of PTM. In S. ingentis, PTM are insoluble in concentrated KOH, dissolve in solutions of chitinase, and are not affected by other hydrolytic enzymes. The permeability of PTM was determined by soaking them in solutions containing various sized tracers. These tests showed that inert particles with diameters greater than 100 nm were unable to penetrate the PTM. This suggests that bacteria and most viruses are too large to penetrate the PTM in S. ingentis unless they can alter the PTM or release toxins that affect PTM formation.