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A simple technique was developed to measure the bacteriolytic activities of the digestive fluids of the deposit-feeding polychaete Arenicola manna. Lysis of a cultured environmental isolate. incubated with extracts of gut lumina1 contents, was monitored spectrophotometrically. Concurrent direct counts were used to verify cell lysis. The ability of extracts from 8 longitudinal sections of the gut to lyse the bacterium was monitored. The digestive ceca, anterior stomach, and posterior stomach regions exhibited high lytic activities, whereas bactenolytic activities in all other regions of the gut were negligible. Sirmlarly, extracts of surface sediments and fecal castings showed negligible lytic capabilities. The sharply limited distribution of lytic activity implicates the ceca as the source of bacteriolytic agent and suggests a true plug-flow system, with little axial mixing. Questions regarding the fate of lytic agents, which disappear abruptly postenor to the stomach, remain unanswered. Localization of lysis in the gut coupled with estimates of gut residence time permit the calculation that ingested bacteria are exposed to strong lytic actlvity for approxin~ately 20 min. Incubation of in situ sediment samples with gut fluids corroborates the distributional findings of the in vitro work although the efficiency of lysis is much reduced, possibly due to exopolymer capsules and slimes of natural sedimentary bacteria. Cross-phyletic comparisons of bactenolytic activities reveal both qualitative and quantitative differences. Much less demarcation of lyhc activity is observed in the guts of a holothuroid (Caudina arenata) and a hernichordate (Stereobalanus canadens~s), with a pattern more similar to that of A. marina observed in another polychaete, Amph~tnte johnstoni. Quantitatively, the polychaetes showed hlgher levels of activity with rates in A. marma exceeding those of the hemichordate and holothuroid by more than 10-fold.

Distribution and efficiency of bacteriolysis in the gut of Arenicola marina and three additional deposit feeders