ELECTROCHEMICAL CHARACTERIZATION OF EXTRACELLULAR POLYMERIC SUBSTANCES AND BIOSURFACTANTS PRODUCED BY GRAM-POSITIVE AND GRAM-NEGATIVE BACTERIA

Abstract

A biofilm can be defined as a community of microorganisms enfolded in a matrix of peptides, nucleic acids, and poly-saccharides that the bacteria release. Planktonic or free-floating microorganisms are produced as a result of these species growing and eventually sloughing off from this matrix, which provides them with a protected environment. The matrix is a sophisticated, three-dimensional structure with attributes that facilitate the effective distribution of waste and nutrients throughout the matrix. Biofilm growth and formation might also be linked with the generation of intermediate bioproducts such as biosurfactants and biopolymers as a result of response to environmental stress. For instance, the biofilm matrix consists of extracellular polymeric substances (or shortly known as EPS), polymers present in nature, typically responsible for structural integrity of the biofilm. The EPS components are secreted by microorganisms to facilitate biofilm growth and adherence to surfaces for further preservation of microbial aggregates. Certain microorganisms, particularly Gram-negative bacteria are able to secrete biosurfactants like rhamnolipids within the biofilm matrix to resist external pathogenic attacks and develop antimicrobial counteractions in the matrix. These so-called ‘intermediate’ bioproducts secreted within the biofilm play a significant part in its growth and are applicable in a variety of industries. Standard test procedures biofilm analysis include mostly chemical and biological methods. However, the characterization of biopolymers can be carried out also with physical methods borrowed from soft matter analysis, such as Electrochemical Impedance Spectroscopy (or EIS). It is already offered in inexpensive equipment and has the potential to become a widespread technique for regular characterization of biomaterials of microbial origin. This study aims to showcase the potential of EIS method to successfully characterize the biopolymers (polyglutamic acid) and biosurfactants (rhamnolipids) secreted by Gram-positive and Gram-negative microorganisms, respectively, and enable to understand how their electrochemical activity behaves.