Increased densities of the bio-irrigator Lanice conchilega affect composition and diversity of nosZ transcripts.

The presence of the piston-pumping polychaete Lanice conchilega can induce short term oscillations in oxygen and nitrate availability at deeper sediment layers, affecting the functional properties of local microbial communities. Here, we investigated the effect of Lanice conchilega densities on the expression of the nosZ gene, a gene encoding for the enzymes involved in the last step (reduction of N2O) of the denitrification pathway. Sediments with “high” , “low” and no Lanice individuals were collected from the intertidal and incubated submerged (reflecting the high water tide) in the lab, to measure vertical oxygen profiles and oxygen oscillations during 35 minutes at 1.5 mm sediment depth before slicing the sediment, and extracting RNA for Illumina sequencing the nosZ gene. We found 502 unique amino acid sequences (“nosZ-UAT), only 21 of them were abundant (>1% relative abundance). nosZ-AUT based community analyses showed that high densities of Lanice significantly affected the nosZ transcript composition. In addition, higher variability was observed in the high density treatments as well. Further differences were observed between the top layer of the sediment (0-0.5 cm) and the investigated deeper layers. The difference in nosZ-AUT Shannon diversity between deeper sediment layers and the upper sediment layer increased with Lanice density. The observed differences in nosZ-AUT composition and diversity at small horizontal (m) and vertical (cm) scale can thus be attributed to differences in bio-irrigator densities. We hypothese that this due to stronger oscillations of both O2 and NO3- availability in the presence of high densities of bio-irrigators. Oscillations of O2 concentrations at a single spot in otherwise anoxic environments create microhabitats where coupled nitrification-denitrification is possible, while providing the environment with NO3- provides substrate for denitrification. As such, the presence of high densities of bio-irrigators increase the effect of already reported tide-related redox oscillations during periods of submersion.

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