Sediment slurry incubations with and without Nereis diversicolor mucus were used to assess how invertebrate mucopolysaccharides affect the structure of the total bacterial and archaeal sediment community.. Invertebrate mucus fuels the microbial nitrogen cycle

Sediment nitrogen cycling is a microbially mediated biogeochemical process that is vital in regulating benthic and pelagic ecosystem productivity. Mucopolysaccharides (mucus) are produced by many invertebrates to aid locomotion and burrowing, and these polysaccharide rich secretions have the potential to be an important source of organic carbon and nitrogen to sediment microorganisms. At present, we have a limited understanding of how mucopolysaccharides impact both sediment microbial communities generally and specific microbial functional groups that drive nitrogen cycling processes. To address this knowledge gap, sediment was incubated with and without Nereis diversicolor mucus. Changes in the concentration of nitrogen compounds (ammonia, nitrite, and nitrate) and in the diversity of the bacterial and archaeal communities were then assessed. With the addition of the mucopolysaccharide sediment carbohydrate concentration increased, which supported a more abundant bacterial community with a distinct community structure. Mucus addition caused an increase in the abundance of bacterial and archaeal ammonia oxidisers, and a concomitant increase in nitrite and nitrate. N. diversicolor mucopolysaccharide appears to enhance sediment nitrification by both fuelling and stimulating key nitrifying microbial groups. We therefore propose that invertebrate mucopolysaccharide secretion should be considered an important and specific bioturbator functional trait when assessing the contributions that invertebrates make to sediment ecosystem structure and function.