244 Abstracts

SECTION 2

BIODEGRADATION OF PERSISTENT ORGANIC COMPOUNDS

Methods of Assessing the Biodegradation of Poly-/I-Hydroxyalkanoates, Role of the SRB

R. Guerrero Department of Microbiology, University of Barcelona, 08028 Barcelona, Spain

Polymer biodegradability in nature is influenced by a series of different environmental variables, as well as by primary polymer properties. Associated processing materials affect the extent of polymer biodegradation. Methods of assessing biodegradation have been developed to quantify the capability of microorganisms to degrade these compounds. Standardized tests may also lead to the search for new microorganisms and environmental conditions that accelerate biodegradation. Because poly-/I-hydroxyalkanoates (PHA) are denser than water, sediments of different water bodies may become the final destination of PHA-based plastic wastes. Since most of these environments have low oxygen content or are complete devoid of oxygen, it is relevant to analyze the anaerobic biodegradation of PHA. We have studied the anaerobic biodegradation of PHA in anaerobic sediments from Lake Cisb (Girona, Spain) and from microbial mats of the Ebro Delta (Tarragona, Spain). Sediments with added PHA showed an increase in sulfide production. The amount of polymer added correlated with sulfide production. Sulfide production was accompanied by polymer degradation. Samples with SRB inhibition by molibdate showed lower degradation percentages than those not inhibited. Degradation was affected by the amount of polymer added. Small quantities of PHA (0.25 and 0.5 mg PHA per cubic centimeter of sediment) were almost completely degraded after 42 days. High quantities of PHA were degraded to a lesser extent (from only 65 to 70%). Intracellular PHA produced by the prokaryotic community represents a major source of organic carbon in the sediment of lakes or microbial mats. The continuous supply of PHA supports the sulfate-reducing activity. Furthermore. the SRB could play a very significant role in the breakdown of PHA in those ecosystems.

Diversity of Anaerobic Microbial Processes in Haloaromatic Degradation

M. M. HPggblom Center for Agricultural Molecular Biolog_v, Cook College, Rutgers University, PO Box 231, New Brunswick, NJ 08903, USA

In the absence of oxygen, a wide variety of alternative electron acceptors can be used by anaerobic bacteria for oxidation of organic compounds. Methanogenesis is predominant in freshwater sediments, while sulfate reduction is a dominant process in carbon metabolism in marine and estuarine sediments. Denitrification can be significant in regions of high nitrate input from agricultural runoff or sewage discharge.

Fe(II1) reduction is important in several sediments and anoxic soils. We have examined the influence of alternative electron acceptors, such as nitrate, iron, sulfate and carbonate on the biodegradability of halogenated aromatic compounds. We have demonstrated that halogenated phenols and benzoic acids can be dehalogenated and degraded to CO* under a variety of redox conditions. Oxidation of the halogenated phenols and benzoic acids to carbon dioxide was coupled to reduction of the respective electron acceptor. The different substrate specificities that we have observed suggest that distinct anaerobic populations are enriched and responsible for the metabolic patterns under the different redox conditions. The interactions and activities of diverse anaerobic communities need to be considered when evaluating the fate of anthropogenic contaminants in the environment and in developing bioremediation technologies.

Microbial Degradation of Cyanide and Nitrile

C. J. Knowles Biological Laboratory, University of Kent at Canterbury, Canterbury, UK

Cyanide, as KCN, NaCN and HCN is produced on a large scale for industrial purposes. Large quantities of cyanide are also found as a by-product and in liquid effluents. Cyanide wastes often contain cyanide as its metal complexes, especially with Fe, Cu. Zn or Ni. Organic cyanides (nitriles; RCN) are produced for a wide range of industrial processes, for example for polyacrylonitrile and polyacrylamide plastics. Again, large scale liquid effluents can occur. Interestingly. substantial amounts of cyanide and nitriles occur in the environment due to natural synthesis, and a wide range of microorganisms are known to be able to biotransform or biodegrade nitriles and cyanide. including metal complexed cyanide. This paper concerns the commercial potential of microorganisms to degrade nitriles and cyanides.

Fungi in Bioremediation

J. W. Bennett, A. Cbildress and K. Wuncb Department of Cell and Molecular Biology, Tulane University, New Orleans, LA 70118. USA

In nature, fungi are among the major decomposers. particularly with respect to plant polymers such as cellulose and lignin. In the laboratory and in the field, most bioremediation strategies have employed bacteria. One reason is that classical microbiological enrichment techniques favor the isolation of bacteria since fungi are slower growing and often require co-metabolic substrates for growth. When supplemental carbon sources and bacteriostatic agents are incorporated into enrichment schemes, fungi are readily isolated. These organisms have the following advantages: (1) the mycelial growth habit allows rapid colonization of substrates, (2) the extracellular nature of the degradative