Biofilms: The Microbial "Protective Clothing" in Extreme Environments

Abstract

Microbial biofilms are communities of aggregated microbial cells embedded in a self-produced matrix of extracellular polymeric substances (EPS). Biofilms are recalcitrant to extreme environments, and can protect microorganisms from ultraviolet (UV) radiation, extreme temperature, extreme pH, high salinity, high pressure, poor nutrients, antibiotics, etc., by acting as "protective clothing". In recent years, research works on biofilms have been mainly focused on biofilm-associated infections and strategies for combating microbial biofilms. In this review, we focus instead on the contemporary perspectives of biofilm formation in extreme environments, and describe the fundamental roles of biofilm in protecting microbial exposure to extreme environmental stresses and the regulatory factors involved in biofilm formation. Understanding the mechanisms of biofilm formation in extreme environments is essential for the employment of beneficial microorganisms and prevention of harmful microorganisms.

Keywords: adaptative mechanism; biofilm; extracellular polymeric substances (EPS); extreme environment; microorganism.

Figure 1

Model of microbial biofilm formation. Biofilm formation consists of five distinct stages: I. Attachment: microbial cells adhere to the surface reversibly. II. Colonization: microbial cells attach to the surface irreversibly via flagella, pili, exopolysaccharides, etc. III. Development: multilayered cells accumulate and produce extracellular polymeric substances (EPS). IV. Mature: stable formation of a three-dimensional community. V. Active dispersal: microorganisms are disseminated from the aggregate biofilm and return to a planktonic state.

Figure 2

A schematic representation of the biofilm function. Biofilm formation can increase the resistances of microorganisms to various extreme environments.