title: Evidence of nitrification and denitrification in high and low microbial abundance sponges.
abstract: Aerobic and anaerobic microbial key processes were quantified and compared to microbial numbers and morphological structure in Mediterranean sponges. Direct counts on histological sections stained with DAPI showed that sponges with high microbial abundances (HMA sponges) have a denser morphological structure with a reduced aquiferous system compared to low microbial abundance (LMA) sponges. InDysidea avara, the LMA sponge, rates of nitrification and denitrification were higher than in the HMA spongeChondrosia reniformis, while anaerobic ammonium oxidation and sulfate reduction were below detection in both species. This study shows that LMA sponges may host physiologically similar microbes with comparable or even higher metabolic rates than HMA sponges, and that anaerobic processes such as denitrification can be found both in HMA and LMA sponges. A higher concentration of microorganisms in the mesohyl of HMA compared to LMA sponges may indicate a stronger retention of and, hence, a possible benefit from associated microbes.
authors.affiliation: Max-Planck-Institute for Marine Microbiology, Celsiusstr. 1, 28359 Bremen, Germany.
authors.forename: Marie-Lise
authors.initials: ML
authors.lastname: Schläppy
authors.affiliation: Max-Planck-Institute for Marine Microbiology, Celsiusstr. 1, 28359 Bremen, Germany.
authors.forename: Sandra I
authors.initials: SI
authors.lastname: Schöttner
authors.affiliation: Max-Planck-Institute for Marine Microbiology, Celsiusstr. 1, 28359 Bremen, Germany.
authors.forename: Gaute
authors.initials: G
authors.lastname: Lavik
authors.affiliation: Max-Planck-Institute for Marine Microbiology, Celsiusstr. 1, 28359 Bremen, Germany.
authors.forename: Marcel M M
authors.initials: MM
authors.lastname: Kuypers
authors.affiliation: Max-Planck-Institute for Marine Microbiology, Celsiusstr. 1, 28359 Bremen, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: de Beer
authors.affiliation: Max-Planck-Institute for Marine Microbiology, Celsiusstr. 1, 28359 Bremen, Germany ; Sars International Centre for Marine Molecular Biology, Thormøhlensgate 55, 5008 Bergen, Norway.
authors.forename: Friederike
authors.initials: F
authors.lastname: Hoffmann