Characterization of biofilm formation in natural water subjected to low frequency variable electromagnetic fields.. biofilm characterization

A device producing and transmitting two waves of harmonic low frequency variable electromagnetic field (EMF) signals into the water passing through it, was studied at the laboratory scale with a view to investigate the effects on the water microbial community and its ability to form biofilm. The application of low frequency variable EMFs to a recirculating circuit fed with natural water enhanced the suspension in water of bacteria and fungi, especially during the first week of treatment. A genetic diversity analysis had revealed the occurrence of bacterial community successions in EMF-treated water throughout the 45 days of experiment, compared with the almost stability observed without this water treatment. Also, microscopic observations, microbial biomass quantification, bacterial diversity analyses and total polysaccharide content showed that the EMF treatment affected the formation and development of biofilm on clean stainless steel slides. Nevertheless, the initial adhesion of bacteria seemed unaffected by the EMF treatment with rapid surface colonization. However, lower biomass adhered onto the slide surface was observed throughout the duration of the treatment, in relation to obvious shifts in the Alpha-, Beta- and Gamma-Proteobacteria during biofilm development. Results might suggest a colloidal dispersion effect of the EMF, affecting the water microbial communities and the biofilm formation. The present study provides the first evaluation of the effects of low frequency variable EMFs on both natural planktonic and biofilm microbial communities.