Cresols and the microorganisms of the soil environment

Phenolic compounds, including cresols, in the soil environment are a result of natural processes such as: biodegradation of lignins and tannins, and anthropogenic activity. Cresols are present in disinfectants as well as in the wastewater from chemical, petrochemical, pharmaceutical, paper and textile industry. They are also used in the production of insecticides, herbicides, medicines and antioxidants and have been classified as hazardous substances. Exposure of microorganisms to cresols can bring about changes in the structure of their cell membranes, resulting in their growth inhibition and cell lysis. However, there is still an untapped bioremediation potential in microorganisms, which are able to participate in the catabolism of cresols, both under aerobic and anaerobic conditions. The typical strategies of the aerobic degradation of cresols include the use of mono oxygenase and dioxygenase enzymes. Thanks to these enzymes, atoms of molecular oxygen initiate fission of the aromatic ring structure. Under anaerobic conditions, the mechanisms of cresol decomposition currently focus on the addition of fumarate, hydroxylation or carboxylation. The effectiveness of microorganisms in the degradation of cresols is not only due to their occurrence in consortia. They are also effective as single strains. The only controversial aspect involves using genetically modified organisms (GMOs) or their genes in the bioaugmentation process. This is because they are strictly selected and target only specific substrates. Due to this, they do not compete with autochthonous microorganisms undergoing natural selection.