Bioprospecting freshwater microalgae for antibacterial activity from water bodies associated with abandoned mine sites

Bacterial resistance to antibiotics necessitates the search for new sources of microorganisms able to produce these needed molecules, which are typically secondary metabolites produced as a protective mechanism. Microalgae can produce a wide range of secondary metabolites as a response to environmental stress but have been the subject of little research as potential sources of antibiotics. As a step towards assessing their potential, we isolated 40 freshwater green microalgae from water bodies with a wide range of metal concentrations and pH values that were near abandoned mine sites in northern Canada. Microalgae from this region and these types of water bodies had not been previously investigated for antibacterial properties. Forty methanolic microalgal extracts were obtained, analysed and tested against Gram-positive and Gram-negative bacteria, and 37.5% inhibited the human pathogen Staphylococcus aureus (Bacilli). This is a higher 'hit-rate' than in previously published results, and furthermore, the minimum inhibitory concentrations against S. aureus were notably much lower than any other reported work. This is the first time such environments have been assessed, and whilst no clear association was observed between the metals and pH analysed and antibacterial activity, the findings indicate that microalgae from anthropogenically stressed environments are a potential source of antibacterial compounds. That is, sites that are typically regarded as having no value and often very negatively perceived are potential sources of valuable bioactive compounds. Therefore, future studies are necessary to determine what environmental thresholds are associated with the antibacterial activity of the freshwater green microalgae thriving in these environments.