Bacteriófagos com potencial de aplicação ao controle de biofilmes em membranas de nanofiltração

Abstract

Nanofiltration membrane systems have been used in oil exploration wells in order to reduce the concentrations of salts and sulfates in sea water used in injections. However, these systems are constantly subject to fouling and corrosion mainly due to microbial growth and biofilm formation, which leads to loss of efficiency and increased maintenance costs. The use of bacteriophages for microbial control today presents a biotechnological alternative applicable to the industrial environment. In this context, the present work aims to evaluate the potential of bacteriophages in controlling microbial growth and biofilm formation in nanofiltration membrane systems in a sulfate removal unit (URS). Therefore, at first, 58 morphotypes of aerobic bacteria present in membrane biofilms were isolated, quantified and molecular analysis performed for identification. Of these, 35 were identified by the Maldi-TOF technique as belonging to the genera Ochrobactrum, Brevibacillus, Streptomyces, Bacillus, Microbacterium, Lysinibacillus sp and Serratia and used in microbial control assays on a bench scale using phages belonging to the collection of the Laboratory of Applied Microbiology (LMA) from UFMG. These phages were then tested for their bacteriolytic potential against these isolates and those that showed greater effectiveness were characterized in in vitro parameters. To verify the polyvalence of the phages, they were submitted to the host spectrum test where most bacterial strains were susceptible to the tested phages. Five of the collection's phages showed lytic efficacy against most bacterial strains. However, the 18C phages of Pseudomonas aeruginosa RLI17 and Serratia marcescens P1 RLI 33 stood out and went on to the other characterizations. In tests evaluating the best virus/host cell ratios, called multiplicity of infection (MOI), 18C showed the highest lytic activity at MOI of 10 for most isolates exposed to infection, with reductions greater than 50%. Phage P1 caused infection with an MOI of 0.01 in part of the isolates, however higher MOIs also stood out for this phage. As for the stability of the phages to physical-chemical factors (temperature and pH), both remained viable for pH values ranging from acidic to basic and resisted the maximum evaluated temperature of 60ºC. Finally, tests were carried out to evaluate the bacteriolytic activity of the phages on nanofiltration membranes, in addition to being stable also in synthetic seawater. Both phages controlled most bacterial isolates to which they were exposed. It is concluded that the evaluated phages showed promise and are good candidates for phage therapy in industrial systems.