The Biolog technique was introduced into ecological studies to estimate metabolic potential of microbial communities. while utilizing carbon substrates (95 or 31x3, depending on the plate type), microbes reduce a colourless dye to violet formazan. The colour is measured spectrophotometrically. This is a rapid and quite convenient method but it has many drawbacks - for example, only microbes that are cultivable and able to grow in high-nutrient conditions contribute to substrate utilization. The method was used mainly to investigate microbial communities from bulk and rhizosphere soil and to estimate the impact of stressors on soil microbial communities.