Tatiana G. Volova, Anatoly N. Boyandin… Biodegradation of Polyhydroxyalkanoates in Natural Water Environments Биодеградация полигидроксиалканоатов в природных водных экосистемах Т. <...> Introduction Polyhydroxyalkanoates (PHAs), representing the developing industry of degradable bioplastics, are good candidates to gradually replace synthetic polymers. <...> As the outputs of PHAs increase, studies examining degradation of these polymers in natural environments acquire increasing signifi cance. <...> PHAs are degraded in biological media to form products innocuous to the environment: carbon dioxide and water under aerobic conditions or methane and water under anaerobic conditions. <...> PHA biodegradation is performed by microorganisms that secrete intra- or extracellular PHA depolymerases, which differ in their molecular organization and substrate specifi city (Jendrossek, Handrick, 2002). <...> Six hundred PHA-depolymerases from various microorganisms have been identifi ed by now; comparison of their amino-acid provided a basis for uniting them in Сибирский федеральный университет sequences 8 superfamilies including 38 families (Knoll et al., 2009). <...> Most PHA-degrading microorganisms contain only one depolymerase, but there are species that have several depolymerases. <...> For example, Pseudomonas lemoignei, one of the best-studied PHA degraders, has at least six extracellular PHA depolymerases, encoded by phaZ1 – phaZ6 genes (Schцber et al., 2000). <...> Three of them are specifi c for P(3HB) and P(3HB-co-3HV) with low 3HV fractions (P(3HB) depolymerases A, B, and D encoded # 169 # Tatiana G. Volova, Anatoly N. Boyandin… Biodegradation of Polyhydroxyalkanoates in Natural Water Environments by the phaZ1, phaZ2, and phaZ3 genes) (Jendrossek, Handrick, 2002). <...> The activity of these enzymes with the homopolyester P(3HV) is below 5 % of the activity obtained with P(3HB) as a substrate. <...> None of the three P(3HB) depolymerases is able to produce clearing zones on opaque microorganisms degrading polymers in different biological media. <...> Microorganisms degrading poly(3-hydroxybutyrate) were fi rst isolated more than 40 years ago (Chowdhury, 1963). <...> The microorganisms identifi ed belonged to several P(3HV)-granulecontaining agar. <...> The two remaining PHA depolymerases (P(3HB) depolymerase C and P(3HV) depolymerase, encoded by phaZ5 and phaZ4 <...>