Xylanase and cellulase activities during anaerobic decomposition of three aquatic acrophytes

Enzymatic activity during decomposition is extremely important to hydrolyze molecules that are assimilated by microorganisms. During aquatic macrophytes decomposition, enzymes act mainly in the breakdown of lignocellulolytic matrix fibers (i.e. cellulose, hemicellulose and lignin) that encompass the refractory fraction from organic matter. Considering the importance of enzymatic activities role in decomposition processes, this study aimed to describe the temporal changes of xylanase and cellulose activities during anaerobic decomposition of Ricciocarpus natans (freely-floating), Oxycaryum cubense (emergent) and Cabomba furcata (submersed). The aquatic macrophytes were collected in Óleo Lagoon, Luiz Antonio, São Paulo, Brazil and bioassays were accomplished. Decomposition chambers from each species (n = 10) were set up with dried macrophyte fragments and filtered Óleo Lagoon water. The chambers were incubated at 22.5ºC, in the dark and under anaerobic conditions. Enzymatic activities and remaining organic matter were measured periodically during 90 days. The temporal variation of enzymes showed that C. furcata presented the highest decay and the highest maximum enzyme production. Xylanase production was higher than cellulase production for the decomposition of the three aquatic macrophytes species.

Cellulase activities during decomposition of a submerged aquatic macrophyte (Utricularia breviscapa): a microcosm assay

Decomposition of lignocellulosic detritus at enzymatic level is the rate-limiting step during aquatic macrophyte decomposition. Assays were carried out to evaluate cellulase activity during decomposition of Utricularia breviscapa; the assays included the following C-sources: leachate, lignocellulosic matrix and integral detritus. The incubations comprised U. breviscapa C-sources added to Oleo lagoon (21° 36'S and 47° 49'W) water maintained in the dark under anaerobic condition at 15°C, 20°C, 25°C and 30°C. Cellulase activity were monitored during 180 days, with the activity showing a time evolution that depended on the temperature and type of detritus: (i) cellulase activity tended to occur earlier with increasing temperatures, but it was less intense than at lower temperatures, (ii) no activity was observed in incubations with leachate, (iii) cellulase activity was observed in the incubation with integral detritus and lignocellulosic matrix and (iv) higher cellulase activity was observed in the incubations with integral detritus at 15°C (P < 0.05).

A decomposição dos detritos lignocelulósicos em nível enzimático é uma etapa limitante da decomposição de macrófitas aquáticas. Experimentos foram realizados para avaliar a atividade da celulase durante a decomposição de diferentes fontes de carbono provenientes de Utricularia breviscapa: lixiviado, matriz lignocelulósica e detritos íntegros. As incubações compreenderam as fontes de carbono de U. breviscapa adicionadas à água da lagoa do Oleo (21° 36'S e 47° 49'W) mantida no escuro à 15°C, 20°C, 25°C e 30°C. As atividades da celulase foram monitoradas durante 180 dias, apresentando uma evolução temporal dependente da temperatura e do tipo de detrito: (i) a atividade da celulase tendeu a ocorrer mais cedo nas temperaturas mais elevadas, porém foram menos intensas, que nas temperaturas mais baixas, (ii) nenhuma atividade foi observada nas incubações com lixiviado, (iii) as atividades da celulase foram observadas nas incubações com detritos integrais e com matriz lignocelulósica e (iv) as atividades da celulase foram mais elevadas nas incubações com detritos integrais à 15°C (P < 0,05).