27] Extracellular polymers of microbial communities colonizing ancient limestone monuments

Abstract

Publisher Summary This chapter discusses the extracellular polymers of microbial communities colonizing ancient limestone monuments. Biofilms are layered microbial communities growing on inert and livingsurfaces in a variety of terrestrial and aquatic environments, including submerged artificial substrata, invertebrate teguments, sediments, soils, and rock surfaces. The exopolymers, mainly composed of polysaccharides, are an important component of such biofilm communities and their functional roles in terms of attachment, nutrient absorption, and protection against desiccation and antimicrobial agents. Given the anionic substituents that these compounds may have, they can interact actively with dissolved ions in aqueous environments and with framework elements in mineral matrices. The implications of such interactions among exopolysaccharides (EPS) and minerals may also include cation mobilization in soils, solubilization of toxic metals, and the dissolution of minerals. On other hand, studies carried out in Mayan archaeological sites (Yucatan, Mexico) have shown that thick microbial biofilms dominated by cyanobacterial populations contributed to the biodegradation of these buildings by supporting growth of organic acid-producing microorganisms and through active boring. These microbial exopolymers may contribute directly to the deterioration processes by interacting through their polysaccharide fraction with metal cations, which could lead to the complexation of soluble calcium, sequestering it from the limestone matrix. This chapter describes procedures to extract and characterize the polysaccharidic fraction of naturally occurring microbial exopolymers associated with epilithic biofilms.