0012-4966/04/0708- © 2004 MAIK “Nauka / Interperiodica” 0330 Doklady Biological Sciences, Vol. 397, 2004, pp. 330–332. Translated from Doklady Akademii Nauk, Vol. 397, No. 5, 2004, pp. 708–710. Original Russian Text Copyright © 2004 by Volova, Gladyshev, Trusova, Zhila, Kartushinskaya. Manufacturing indestructible synthetic plastics has reached 140 million tons for year, and accumulation of them in natural environment poses a global ecological problem [1]. For this reason, the design and develop- ment of biodegradable plastics that enter biospherical cycles is consistent with the concept of ecologically safe sustainable industrial development. Polyhydroxy- alkanoates (PHA)—biodegradable and thermoplastic polymers that are close in their physicochemical prop- erties to polypropylene and polyethylene—have been intensively studied today [2, 3]. Various bacteria classi- fied with widespread soil and aquatic microorganisms (genera Pseudomonas, Alcaligenes, Comamonas, and Streptomyces) are effective destructors of PHAa [4]. As the prospects of PHA exploitation increase, stud- ies of consistent patterns of degradability under natural conditions become extremely topical. The goal of this work was to study the time course of PHA degradation in a fresh water body and to identify microorganisms involved in this process. Experiments were performed during summer field seasons (1999–2001) in a small recreational eutrophic reservoir on the Bugach River, a secondary confluent of the Enisei River (area, 0.32 km 2 ; depth, up to 8 m), which is located near Krasnoyarsk. In summer, this water body is prone to blooming due to the presence of cyanobacteria. We used PHA samples of two types, which were synthesized by the bacteria R. eutropha B5786 according to the technology developed in the Institute of Biophysics, Siberian Division, Russian Academy of Sciences. The first sample was homopoly- mer of PHB (molecular weight, 340 kDa; degree of crystallinity, 76%); the second, copolymer PHB/PHV (hydroxyvalerate proportion, 14 mol.%; molecular weight, 140 kDa; degree of crystallinity, 52%). Prelim- inarily weighed polymer samples in the form of film discs (diameter, 40 mm; thickness, 0.07–0.10 mm) were placed in nylon traps at a depth of 1 m. The deg- radation rate of polymers was evaluated by a decrease in molecular weight. At certain time intervals, discs were extracted from traps, washed with distilled water, dried, and weighed again. Simultaneous analysis of the state of the water-body ecosystem included the deter- mination of water temperature, chlorophyll and oxygen content, and the total number of bacteria and microal- gae. To isolate bacteria involved in the bioplastic degra- dation, films obtained from PHB/PHV were exposed in the pond for 42 days (from September 5 to October 17, 2000) in 2-l plastic bottles at a depth of 0.5 m; the con- trol bottle without PHA was exposed under similar con- ditions. Selected experimental and control water sam- ples, as well as wash-out water from films, were ana- lyzed by gradient electrophoresis under denaturing conditions [5]. Species of microorgamnisms were iden- tified using phylogenetic analysis based on a sequenced fragment of the 16S RNA gene. The process of PHA degradation in the pond during the period of observation (several field seasons) was characterized by certain differences. For example, in summer 1999, PHB-based films were degraded practi- cally at the same rate throughout the study period (42 days). During this time, bioplastic weight decreased by 43.5%; the specific degradation rate (μ) was 0.011 mg day –1 . PHB/PHV-based films were degraded much more rapidly, with the time course of degradation being characterized by a pronounced pha- sic mode. The phase of absence of reliable changes in film weight during the first 14 days was followed by the phase of intensive degradation of the polymer. In the first experiment, which encompassed the period from June 16 to July 21, there was a two-week lag period with subsequent 21-day period in July, when water tem- perature markedly increased. During this period, films were almost completely degraded (residual weight was 0.7% of the initial value) at an average μ value of 0.129 mg day –1 . The time course of degradation of PHB/PHV-based films in the second experiment (the period from July 21 to August 12) was similar. How- ever, in August, the specific degradation rate of films was higher (0.174 mg day –1 ). The observed difference in the rates of degradation of PHB and PHB/PHV is consistent with the common idea that homogeneous PHB/PHV, which has a greater degree of crystallinity and refractoriness, is less acces- sible for degradation by microorganisms and enzymes, compared to PHB/PHV with a lower crystallinity. This GENERAL BIOLOGY Degradation of Bioplastics in Natural Environment T. G. Volova, M. I. Gladyshev, M. Yu. Trusova, N. O. Zhila, and M. V. Kartushinskaya Presented by Academician I. I. Gitel’zon February 9, 2004 Received February 18, 2004 Institute of Biophysics, Siberian Division, Russian Academy of Sciences, Akademgorodok, Krasnoyarsk, 660036 Russia