A Doubling of Microphytobenthos Biomass Coincides with a Tenfold Increase in Denitrifier and Total Bacterial Abundances in Intertidal Sediments of a Temperate Estuary

Abstract

Surface sediments are important systems for the removal of anthropogenically derived inorganic nitrogen in estuaries. They are often characterized by the presence of a microphytobenthos (MPB) biofilm, which can impact bacterial communities in underlying sediments for example by secretion of extracellular polymeric substances (EPS) and competition for nutrients (including nitrogen). Pyrosequencing and qPCR was performed on two intertidal surface sediments of the Westerschelde estuary characterized by a two-fold difference in MPB biomass but no difference in MPB composition. Doubling of MPB biomass was accompanied by a disproportionately (ten-fold) increase in total bacterial abundances while, unexpectedly, no difference in general community structure was observed, despite significantly lower bacterial richness and distinct community membership, mostly for non-abundant taxa. Denitrifier abundances corresponded likewise while community structure, both for nirS and nirK denitrifiers, remained unchanged, suggesting that competition with diatoms for nitrate is negligible at concentrations in the investigated sediments (appr. 1 mg/l NO3 -). This study indicates that MPB biomass increase has a general, significantly positive effect on total bacterial and denitrifier abundances, with stimulation or inhibition of specific bacterial groups that however do not result in a re-structured community.

Controls on microalgal community structures in cryoconite holes upon high Arctic glaciers, Svalbard

“…These granules provide a substrate for growth of surprisingly high biomasses and diversities of bacteria, cyanobacteria, eukaryotic microalgae and protozoa (Mueller et al, 2001;Christner et al, 2003;Cameron et al, 2012). Additionally, invertebrates mainly comprised of tardigrades and rotifers have been found inhabiting cryoconite holes on glaciers worldwide (De Smet and van Rompu, 1994;Grongaard and McInnes, 1999;Säwström et al, 2002;Porazinska et al, 2004;Zawierucha et al, 2014). The species diversity of these grazing invertebrates is relatively low and relatively well known but their ecological role in the cryoconite community has not been addressed yet.…”

“…The species diversity of these grazing invertebrates is relatively low and relatively well known but their ecological role in the cryoconite community has not been addressed yet. It is believed that they act as top predators in a microbial food web consisting of both grazing and carnivorous species (De Smet and van Rompu, 1994).…”

Deep nirS amplicon sequencing of San Francisco Bay sediments enables prediction of geography and environmental conditions from denitrifying community composition

“…The clone library and PGM datasets were generated using the same forward primer but different reverse primers; in both cases, we clustered sequences into OTUs at the 88% identity level. In agreement with other studies using NGS (Bowen et al ., ; Decleyre et al ., ; Saarenheimo et al ., ), the deeper sampling provided by PGM increased estimates of the total diversity in each sample. The Chao 1 richness estimate for the clone library ranged between 8 and 179 OTUs per sample with a mean of 50.5; for the PGM dataset it ranged between 226 and 683 OTUs per sample with a mean of 441.2 (Fig.…”

“…A small number of studies have also recently adapted NGS techniques to target the nirS gene in environments such as salt marsh sediment (Bowen et al, 2013), boreal lake sediment (Saarenheimo et al, 2015), and estuarine sediment (Decleyre et al, 2015). One striking finding in common among all of these studies is the measurement of greater nirS diversity than had been described previously.…”

“…One striking finding in common among all of these studies is the measurement of greater nirS diversity than had been described previously. Whereas earlier clone library studies typically failed to saturate the predicted OTU richness in the functional gene (Santoro et al ., ; Mosier and Francis, ; Francis et al ., ), more recent studies using 454 pyrosequencing achieved coverage values of > 90% (Decleyre et al ., ; Saarenheimo et al ., ) and a higher number of observed OTUs. Notably, NGS‐based studies have employed a broader OTU definition (80–90% similarity) than the 95% similarity typically used by clone library studies of nirS , which means that the increase in observed diversity is actually even greater than it appears.…”