Study on Adhesion of Bacterio-contaminants to Fragments of Rocks Immersed in Water: Impact of Some Chemical Properties of the Medium and Intrinsic to the Cells

Abstract

A study was carried out in an aquatic microcosm with the aim of evaluating the importance of some chemical factors of the environment and some parameters intrinsic to cells, on the retention of bacterial contaminants in the aquatic environment on solid substrates. The rocky substrates used were sandstone, basalt, granite and micaschist. Four rocks with different petrographic and mineralogical structures. Bacteria isolated by standard techniques and used for adhesion testing were Pseudomonas aeruginosa, Vibrio cholerae and Enterococcus faecalis. These bacteria are rod, comma, and spherical in shape, respectively, and may or may not have a flagellum. In addition, this ciliature, when it exists, can be single or in a tuft and in a polar position or over the entire cell. The chemical parameters of the medium which varied were the pH, the concentrations of BOM and of salts. The incubation periods to allow the bacteria to adhere to the substrates ranged from 180min to 1440min. The adhered cells were then detached in sterile condition by introducing the rocks successively into 3 test tubes containing 10 ml of sterile physiological water (0.85% NaCl). It appears that bacteria contained in surface or groundwater can adhere to the surfaces of inorganic rocks at varying concentrations. The adhesion and retention of bacteria contributes to the natural purification of wastewater. P. aeruginosa, V. cholerae and E. faecalis adhered undergo temporal variations. Adhesion rates overall vary from 11 to 12.44x103 cells/cm2/h, with E. faecalis being the bacteria which adheres more quickly due to gravity alone. These variations of rates are linked to environmental conditions and to the chemical properties of rocks and soil. The presence of flagellum plays a dual role in approaching and relaunching the bacteria from the substrates.