Influence of Heavy Metals and Arsenic on Survival and Biofilm Formation of Some Saprotrophic Soil Microorganisms

This study was aimed at studying the effect of heavy metals and arsenic on the survival and biofilm formation of some saprotrophic microorganisms: Bacillus megaterium var. phosphaticum, Bacillus mucilaginosus, Pectobacterium carotovorum, and Escherichia coli. As a source of heavy metals and arsenic, we used aqueous solutions of NaAsO2, Cd(CH3COO)(2), and Pb(NO3)(2) (2.5, 25, 250 mg L-1). The cultures in the liquid medium had different resistance to the toxicants under study: B. megaterium > B. mucilaginosus > P. carotovorum > E. coli. The toxicity of the tested solutions of heavy metals and arsenic for microorganisms can be arranged (decreasing toxicity) as follows: cadmium acetate > lead nitrate > sodium metaarsenite. These experiments revealed some regularities related to the mechanisms of toxic effect of As, Pb, and Cd solutions on the formation of biofilms of soil bacteria, changes in bacterial cellular forms, and their survival. Bacillus megaterium strain was the most resistant to high As concentrations and was able to influence the formation of highly structured colonies of bacterial cells with the honeycomb-like structure. The immobilization of heavy metals can be achieved due to their binding into strong compounds with the matrix substances of biofilms and polymeric organic compounds formed during the sporulation of rhizobacteria. It can increase the resistance of bacteria to high concentrations of heavy metals and arsenic. The results obtained can be of great practical importance in the development of biotechnologies related to soil bioremediation, in the field of nanotechnology, crop production, and medicine.