Analysis of Electrophysical Profiles of Planktonic and Biofilm Cells for Azospirillum baldaniorum

Biofilm formation is a widespread phenomenon in the microbial world. They may affect human and animal health and cause damage to various industries; at the same time, they can be useful in such fields as wastewater treatment or improving bioavailability of nutrients for plants. This fact actualizes the development of methods for studying biofilms. The present work is the first report on an optical sensor technique for the indication of bacterial biofilm formation with regard to biological variability, using plant growth-promoting rhizobacteria of the genus Azospirillum as a model. The correlation was found between the changes in electrophysical parameters recorded by the sensor system and the morphological features of bacteria from planktonic and/or biofilm cultures: the presence of motile organelles (flagella), polymorphism, and ultrastructure of cellular forms. It was established that the profiles of microbial cells recorded by the optical system were significantly different in planktonic and biofilm forms. When comparing the cells of different strains (the parental strain and its derivatives), or planktonic and biofilm bacteria, the variables recorded by the electro-optical sensor system were in agreement with the changes in bacterial micro- and ultrastructure recorded by other techniques. The results of analysis of the electrophysical profiles of A. baldaniorum Sp245 can be used as reference for revealing specific interactions between biofilm cells of this strain and various root surface components of a putative plant partner using an optical sensor system.