DISTRIBUTION AND EFFICIENCY OF BACTERIOLYSIS IN THE GUT OF ARENICOLA-MARINA AND 3 ADDITIONAL DEPOSIT FEEDERS

A simple technique was developed to measure the bacteriolytic activiti es of the digestive fluids of the deposit-feeding polychaete Arenicola marina. Lysis of a cultured environmental isolate, incubated with ext racts of gut luminal contents, was monitored spectrophotometrically. C oncurrent direct counts were used to verify cell lysis. The ability of extracts from 8 longitudinal sections of the gut to lyse the bacteriu m was monitored. The digestive ceca, anterior stomach, and posterior s tomach regions exhibited high lytic activities, whereas bacteriolytic activities in all other regions of the gut were negligible. Similarly, extracts of surface sediments and fecal castings showed negligible ly tic capabilities. The sharply limited distribution of lytic activity i mplicates 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 posterior to the st omach, remain unanswered. Localization of lysis in the gut coupled wit h estimates of gut residence time permit the calculation that ingested bacteria are exposed to strong lytic activity for approximately 20 mi n. Incubation of in situ sediment samples with gut fluids corroborates the distributional findings of the in vitro work although the efficie ncy of lysis is much reduced, possibly due to exopolymer capsules and slimes of natural sedimentary bacteria. Cross-phyletic comparisons of bacteriolytic activities reveal both qualitative and quantitative diff erences. Much less demarcation of lytic activity is observed in the gu ts of a holothuroid (Caudina arenata) and a hemichordate (Stereobalanu s canadensis), with a pattern more similar to that of A. marina observ ed in another polychaete, Amphitrite johnstoni. Quantitatively, the po lychaetes showed higher levels of activity with rates in A. marina exc eeding those of the hemichordate and holothuroid by more than 10-fold.