Isolation and identification of new microalgae strains with antibacterial activity on food-borne pathogens. Engineering approach to optimize synthesis of desired metabolites

Abstract

This paper presents a strategy for isolation, identification and evaluation of microalgae strains synthesizing biologically active compounds (BAC) with antimicrobial activity against food-borne and other pathogens. Water samples containing microalgae were initially submitted to the enrichment process, followed by standard procedure for obtaining pure culture. Purified DNA from the microalgae isolates was used for sequencing the amplified 18S rDNA genomic region, which resulted in the identification of Poterioochromonas malhamensis, Chlorella sp., Micractinium sp., Tetradesmus sp. and Desmodesmus sp. All isolated strains were cultivated in 1-L flat-plate PBRs, with the Poterioochromonas malhamensis being the only one to show antibacterial activity in agar diffusion assay. Further, PPEQ-01strain was cultured under different types and scales of PBR, intensity and spectrum of the incident light, in order to study and prove the antibacterial potential of the strain. Ethanolic and methanolic supernatants, or hydrophilic and methanolic extracts produced from biomass cultivated in different conditions led to formation of bacterial growth inhibition halos around the impregnated disks used in the agar diffusion test. The hydrophilic extract, obtained from biomass cultured under green illumination, exhibited stronger activity against all tested pathogenic bacteria as compared to the other extracts. The results obtained with the new isolated Poterioochromonas malhamensis strain proved efficiency of the innovative complex approach applied to BAC aiming the identification of microalgae that present antimicrobial activity.