Exopolymer microenvironments of microbial flora multiple and interactive effects of trophic relationships. Limnol Oceanogr 38:1633–1645

Microbial cells in natural environments arc often encased in different types of exopolymcr secretions (EPS), ranging from tight capsules surrounding individual cells to the looser slime matrices of biofilms. The diffcrcnt physical and chemical propertics of exopolymers could have secondary effects on trophic interactions between microbial cells and consumer animals. Laboratory studies showed that capsule EPS is significantly less digestible to consumers than slime EPS, even when extracted from the same bacterial strain. Bacterial cells with EPS capsules are less efficiently digested than noncapsuled cells, suggesting that capsules protect against digestion. Follow-up experiments determined that polysaccharide-rich fractions of slime EPS are absorbed with very high eficiencies while protein portions, which are more abundant in capsular polymers, are absorbed relatively poorly. Another series of cxpcriments showed that dissolved organic matter (DOM), when adsorbed directly to the mineralogical portions of sediment particles, is available to deposit feeders. However, the further presence of an exopolymer coating on sediments more than doubled the bioavailability of adsorbed DOM to the consumer. Observations using cold-stage scanning electron microscopy indicated that exopolymer microenvironments are a common feature of natural marine sediments. Microbial exopolymers range from easily digestible carbon sources to relativel