Enzymatic activities of epiphytic and benthic thraustochytrids involved in organic matter degradation

Thraustochytrids are marine osmo-heterotrophic protists which have been isolated from different habitats and substrates. These organisms are typically encountered in association with refractory substrates, but the extent of their role in organic matter decomposition is still unknown. We isolated 11 thraustochytrid strains from different substrates and tested all species for their potential constitutive ecto- (cell-surface associated) and exo- (free released) enzymatic activities. Our results indicate that the investigated strains exhibited a wide spectrum of enzymes involved in the hydrolysis of all classes of organic compounds, suggesting that thraustochytrids are capable of degrading a large variety of substrates. The enzymatic pools were similar among all strains, and exhibited a good production of lipase, a selection of protease and a poor pool of carbohydrate degradation enzymes. However, different isolates displayed different spectra and intensities of enzymatic activities. The comparison of enzymatic activities of 2 thraustochytrid strains and the total enzymatic activities measured in their natural substrates suggested that thraustochytrids, although representing a minor fraction of the total benthic microbial biomass, are contributors to the degradation of highly refractory organic compounds.