Resumo

Mangroves are areas with a high biological diversity. Because of the typical vegetation, root systems and reduced tidal flow, there is a large scale accumulation of organic, inorganic and plastic wastes in this very important ecosystem. Heterotrophic bacteria show high degree of variability in their metabolic capabilities resulting from a great range of enzymes with different substrate specificities in soil. As a result of this natural process, wastes are either used up or converted into a less harmful products. On the other hand, low-density polyethylene (LDPE), accounts for 60 % of the total plastic production and is the most commonly found solid waste is the non-degradable polythene carry bags. Their indiscriminate use and discard, although the awareness campaigns of reducing, reusing and recycling, are an environmental problem for most of the coastal areas containing large quantity of this highly recalcitrant waste material. The purpose of this study was estimating the bacterial diversity of the mangrove from a North coast area of the State of Alagoas (Northeastern Brazil), with special emphasis on determining their ability to degrade the polythene wastes. The bacterial diversity was analyzed by morphological/ biochemical tests, after serial dilution of the collected soil and inoculation of it in Nutrient Agar (the load was determined by the plate count method, after 24 h of incubation at 28 ^oC). The ability of the bacterial isolates to produce various extracellular hydrolytic enzymes were determined using the substrate-plate assay. There was a predominance of the gram negative genera Pseudomonas, Aeromonas and Neisseria. Other genera encountered included Staphylococcus, Micobacterium and Corynebacterium. Their effectiveness on the degradation of commercial plastic bags made of high density polyethylene (HDPE) and LDPE was studied in the laboratory after 60 days. Biodegradation was measured in terms of average weight loss, which was ca. 7 % in the end of the analyzed period. There was a significant increase in the bacterial load of the soil attached to class 2 HDPE (mainly Pseudomonas, Corynebacterium and Staphylococcus). In mangrove soil attached to class 1 there was a predominance of Aeromonas + Neisseria + Micobacterium, whilst in soil with class 3 plastic - the one that suffered the greatest biodegradation, occurred predominance of Pseudomonas + Neisseria+ Corynebacterium. While most of the isolates produced most of the hydrolytic enzymes (amylase, cellulase, xylanase, caseinase, esculinase, fenolase and gelatinase), the lipolytic activity was low.