Exopolymer microenvironments of microbial flora: Multiple and interactive effects on trophic relationships

Abstract

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 relatively refractory ones that effectively protect some microbial cells from consumer digestion. Exopolymer microcnvironments may also make recently adsorbed DOM highly accessible to particle-ingesting animals.

The effect of carbohydrate production by the diatom Nitzschia curvilineata on the erodibility of sediment

“…Carlton and Wetzel (1988) showed that epipelic algal photosynthesis, or the magnitude of sediment oxygenation, was inversely correlated with the phosphate efflux rate from lake sediments. The associated production of carbohydrates in response to the nutrient-depleted conditions may slow down the diffusion of ions and contribute to the conservation of nutrients in sediment (Decho 1994). Primary production in the overlying water may be affected by the formation of bubble mats if nutrients become conserved within the sediment.…”

“…An dxopolymer matrix is a highly labile source of carbon and e$hibits highly adsorptive qualities that allow it to sequester dissolved organic matter (Decho and Lopez 1993). The flux of this material to the overlying water column can serve as a measure of food availability, an important parameter not often considered in the development of carrying capacity models for shellfish aquaculture in coastal embayments (Dowd 1991).…”

“…The production and composition ("stickiness") of carbohydrates depends on several factors including nutrient status and growth phase (Decho 1990). The objective of this paper is to determine the effect of carbohydrate production by the benthic diatom Nitzschia cuwilineata on the erodibility of permanently submerged sediments.…”

Ecological role of exopolysaccharides of Bacillariophyta: A review

“…Одной из главных функций ЭПС в морских экосистемах является биостабилизация осадков, необходимая для сохранения структуры подверженных эрозии литоральных зон (Paterson, 1989;Decho, 1990;Decho et al, 1993). Они заполняют межклеточное пространство микробных агрегатов и формируют структуру матрикса биопленок.…”

Biochemical characterization of some cyanobacterial strains from salt marshes of the Venice Lagoon

“…Cyanobacteria are pioneer species with good adaptive skills, able to colonize barren sediments and soils, fix nitrogen and carbon, and regulate moisture-producing exopolymeric secretions: bacterial capsules, sheaths, and slime of hydrophilic polysaccharides (Decho and Lopez 1993) with variable water content that change with environmental conditions and strain type. These polysaccharides act as protection from sudden osmotic changes and desiccation (Klock et al 2007), allowing cell adhesion to substrata.…”