Bacterial exopolymers - Literature review

Improving our understanding of the interactions between micro-organisms and minerals as well as the practical exploitation of biological activity for specific applications is the primary vocation of the BIOPROC project. They are an essential source of expertise for projects such as acid mine drainage, hydrogeochemical modelling and the implementation of reactive barriers for soil and groundwater remediation. In this context, the 'Biochemistry' module of the BIOPROC project was designed to study more specifically the enzymatic systems and excreted molecules involved in mineral-bacterial interactions. The first phase of this work consisted of a synthesis of the state of the art, which is the subject of this report. This study is devoted to literature data on excreted bacterial molecules that play a role in their adhesion to substrates. The bulk of this literature review is devoted to bacteria involved in the sulfur cycle (oxidation and reduction), a subject on which the EPI/BIO team has acquired significant scientific and technical knowledge. It also shows that this theme may have other possible applications, notably in the bioremediation of environments polluted with heavy metals. his synthesis shows that the vast majority of micro-organisms grow in aggregated form and attach themselves to a matrix using extracellular polymeric compounds (or substances), commonly known as EPS (Extracellular Polymeric Substances). Their chemical composition is highly varied, with polysaccharides being the main component. However, proteins, nucleic acids and (phospho)lipids have also been identified. EPS can be released from the bacterium in a number of different ways: active secretion, spontaneous release from the cell surface or from membrane vesicles, cell lysis... Studies of EPS and their functions require the use of a wide range of methods and techniques, which can be quite tricky to set up due to the complex organization and composition of bio-aggregates. EPS extraction, purification and analysis stages are based on skills in microbiology, biochemistry, physics, microscopy and electrochemistry. All the data show that EPS are primarily responsible for the structure of biofilms. They are also involved in the leaching, corrosion, deterioration and sorption of elements such as metals. They are also responsible for the resistance of micro-organisms to certain biocides. Their properties make them compounds with potential applications in the environment, food industry, cosmetics, medicine and pharmacology... In terms of the main lines of research developed at BRGM, the characterization and functional studies of EPS are of great interest. This theme can contribute to a better understanding of interactions between bacteria and mineral supports, and to the characterization of biofilm formation. Exploiting of the properties of EPS and biofilms may also lead to the development of new pollution control processes. Possible areas of application for such studies include bioleaching, bioremediation of environments polluted with heavy metals, geomicrobiology and the fight against problems linked to the development of biofilms (water treatment, geothermal energy, etc.).