Selective Feeding of Bdelloid Rotifers in River Biofilms

Abstract

In situ pigment contents of biofilm-dwelling bdelloid rotifers of the Garonne River (France) were measured by high performance liquid chromatography (HPLC) and compared with pigment composition of surrounding biofilm microphytobenthic communities. Among pigments that were detected in rotifers, the presence of carotenoids fucoxanthin and myxoxanthophyll showed that the rotifers fed on diatoms and cyanobacteria. Unexpectedly, while diatoms strongly dominated microphytobenthic communities in terms of biomass, HPLC results hinted that rotifers selectively ingested benthic filamentous cyanobacteria. In doing so, rotifers could daily remove a substantial fraction (up to 28%) of this cyanobacterial biomass. The possibility that the rotifers hosted symbiotic myxoxanthophyll-containing cyanobacteria was examined by localisation of chlorophyll fluorescence within rotifers using confocal laser scanning microscopy (CLSM). CLSM results showed an even distribution of quasi–circular fluorescent objects (FO) throughout rotifer bodies, whereas myxoxanthophyll is a biomarker pigment of filamentous cyanobacteria, so the hypothesis was rejected. Our results also suggest that rotifers converted β-carotene (provided by ingested algae) into echinenone, a photoprotective pigment. This study, which is the first one to detail in situ pigment contents of rotifers, clearly shows that the role of cyanobacteria as a food source for meiobenthic invertebrates has been underestimated so far, and deserves urgent consideration.

Legionella-protozoa-nematode interactions in aquatic biofilms and influence of Mip on Caenorhabditis elegans colonization

“…and Centropyxis sp., indicating the specificity of the applied inoculation assay (Lahr et al, 2008;Lara et al, 2007). Of the metazoan species identified in the biofilm (Copepoda, Nauplius larvae, and Rotifera sp., nematodes), only nematodes accumulated L. pneumophila within their intestines (Bruno et al, 2012;Mialet et al, 2013;van Lieverloo et al, 2004). This finding further strengthens the view that nematodes may be an additional reservoir of L. pneumophila in aquatic habitats.…”

Short-term effects of nutrient enrichment on river biofilm: N–NO3 − uptake rate and response of meiofauna

“…Indeed, benthic rotifers can consume a wide variety of preys such as algae, bacteria and yeast (e.g. Ricci & Balsamo, 2000;Duggan, 2001;Mialet et al, 2013). Moreover, previous studies report that the response of lacustrine meiofauna to nutrient addition differs amongst meiobenthic taxa (Särkkä, 1992;Wu et al, 2004;Ristau & Traunspurger, 2011;Ristau et al, 2012).…”

“…Alternatively, since microalgal production was not measured, it can be envisaged that microalgal production might have been stimulated even though their biomass did not change. Considering that rotifers are effective grazers in river biofilms (Kathol et al, 2011;Mialet et al, 2013), the grazing of algae by increasing density of rotifer might on the one hand favour bacteria in the competition for N-NO 3 -and on the other hand keep the algal population in an active growth phase and hence stimulate N-NO 3 -uptake of the biofilms at high N-NO 3 -concentration. We can, hence, not exclude that stimulated microalgal growth also participated in the increased N-NO 3 -uptake in the enriched conditions.…”

“…benthic invertebrates passing through a 500 lm mesh sieve and retained on 50 lm meshes, Giere, 2009) are extremely abundant in epilithic river biofilms (Gaudes et al, 2006;Majdi et al, 2012a). Although their grazing pressure on biofilm microphytobenthos is rather low (Majdi et al, 2012b, c;Mialet et al, 2013), their activity within the biofilm can affect oxygen turnover (Mathieu et al, 2007) and seemingly other key processes such as biofilm detachment and the release of secondary metabolites in the water column (Sabater et al, 2003;Gaudes et al, 2006). Recently, Derlon et al (2013) have shown that, in gravity-driven membrane filtration water depuration systems, the presence of nematodes and oligochaetes increases the heterogeneity and porosity of membrane-associated microbial biofilms, and consequently increases the efficacy of filtration process used to treat organically polluted waters.…”

TAXAS DE FILTRAÇÃO E INGESTÃO DE UMA MICROALGA POR Philodina roseola (Rotifera: Bdelloidea)

“…Mialet et al (2013) em um experimento in situ com rotíferos bentônicos da Subclasse Bdelloidea, mostraram que os rotíferos ingeriram seletivamente as cianobactérias filamentosas e ao fazerem isso removeram diariamente uma parte substancial (até 28 %) da biomassa de cianobactérias do corpo d'água estudado. Lionard et al (2005) analisaram e compararam a eficiência de filtração do micro e mesozooplâncton sobre o fitoplâncton em experimentos in situ utilizando amostras de água natural de três distintos estuários.…”