Extracellular polymeric substance

theoretical functions of soil EPS

Overview

Extracellular polymeric substances (EPS) are a group of substances exuded by microorganisms in order to form biofilms. The major components are extracellular polysacharides (also called EPS), protiens, DNA, enzymes, lipids, and other biopolymers. EPS accounts for 90% of biofilm drymass and constitutes the matrix of the biofilm. Biofilms are microhabitats that keep microbes attached to a substrate, provide protection from desiccation , and play a key role in nutrient cycling. Biofilms are also known to alter the structure , hydrology , and composition of soils.

Functions

EPS works at the smallest levels of soil aggregate formation

Habitat stability: The suspected primary role of EPS is to create stable habitat bound to a desired substrate[]. Very common substrates are soil particles within the soil pore matrix however, many surfaces can be used to create biofilms with EPS. Biofilms are very effective at retaining water in soils even with very negative water potentials.[]

Chemical reactions: EPS provides a stable interface for soil microbes to chemically work on attached substrate and suspended materials. In addition EPS itself is a store of carbon and other nutrients. The binding nature of EPS also helps reduce nutrient loss in soils from runoff.[]

Hydrology: EPS resists evaporation by binding the water tightly[]. The biofilms formed with EPS can cause bioclogging of pores which resists evaporation and mass flow of water by reducing the hydraulic conductivity[]. This slows the rate of change in soil moisture content.

Soil structure: EPS production fills soil pore space which reduces the effective average pore size[]. For the potential impacts of this see [porosity]. Also, the swelling shrinking actions of EPS water intake and loss can alter the pore space but there remains a lack of literature differentiating this effect in bulk soil[]. EPS plays a key role in soil aggregate formation by working as a cementing agent. This has the added effect of reducing soil slaking and increasing overall stability. This added stability can lower erosion rates and decrease nutrient runoff.

Plants: There is evidence to suggesting that, in addition to liberating soil bound nutrients, EPS may assist in salinity tolerance for some plants.[(Ashraf et al. 2004)]

Agriculture: There is growing interest in using EPS producing bacteria because they improve soil particle aggregation which improves agricultural soil health.[(Costa et al. 2018)]

Analysis methods: Cation exchange resin (CER) is currently considered the best method for accurately estimating EPS composition in soil.[(Redmile-Gordon et al. 2014)]