Abstract
The oceans have been compared to a “global heterotrophic digester”. This is due to the high productivity of microalgae and the rapid turnover of the produced biomass by microbes. A major part of the algal biomass consists of diverse polysaccharides which belong to the most complex polymer structures in nature. These marine sugars are decomposed by specialized bacteria, mainly of the phyla Bacteroidetes and Gammaproteobacteria, which possess dedicated conserved gene clusters encoding a remarkable diversity of carbohydrate-active enzymes.