Role of EPS in cryptoendolithic communities in an arid habitat

Harry D Kurtz Jr

Role of EPS in cryptoendolithic communities in an arid habitat

Harry D Kurtz Jr

Clemson University, USA

: Expert Opin Environ Biol

Abstract

Within the barren sandstone outcrops found in the Grand Staircase-Escalante National Monument in southern Utah, diverse microbes exist in the pore spaces of the rocks. Dominated by cyanobacteria, these communities harbor a diverse collection of bacteria, including potential iron-reducing bacteria. As a community, these cryptoendolithic microbes affect the larger landscape through their production of extracellular polysaccharide (EPS). Through the production of EPS and filamentous cells, these communities harden the stone surface, making it more resistant to the effects of wind and water. Cell mass and EPS also clog pores within the rock surface, reducing the rate of water infiltration. These physical effects resulting from EPS production are likely passive phenomena. EPS extracted from these communities can bind ferrous iron, potentially arising from the activity of iron-reducing bacteria. Biochemically, active preparations of the EPS were rich in uronic acids, making the polysaccharides acidic in nature. Fractions of the EPS obtained from lab grown consortia include a soluble fraction found in culture supernatants and an insoluble component that is tightly associated with the cell mat. We have found that cobalt ions will interfere with the iron binding activity of the EPS, suggesting that these EPSs bind multiple cations. Functionally, the EPS would serve to sequester and concentrate available cations from the ecosystem, making them available for uptake by cyanobacteria and other community members for metabolic purposes. When we include the movement of water through the communities via evaporation, we hypothesize that the system serves as a bio-filter to capture essential metal ions.