two natural bacterium culture, isolated from raadi lake water (tartu, estonia), aeromonas hydrophila p69.1 and pseudomonas fluorescens p75 were used for construction of BOD biosensor. both strains of bacterial cultures were procured from bacterial library of institute of technology, university of tartu. all bacteria in the library are kept in glycerol solution at -80oc. the selection of the microorganism for semi-specific biosensor was based on their ability to use fat as a substrate due to high oil and grease concentration in meat industry wastewater. the liolytic properties were examined by culturing bacteria in medium containing 0.1% swine fat (rakvere meat industry) as the only carbon sourch. A. hydrophilla culture was selected due to fast growth rate in the given medium. non-specific bacteria, P. fluorescens, that was also used as a reference in previous studies, were used as comparison to illustrate the advantages of semi-specific bacteria.