Viability of differentiated epilithic bacterial communities in the River Garonne (SW France)

Abstract

Epilithic bacterial community viability was assessed on natural biofilm assemblages from environmentally contrasting locations over a 17-months period to determine if it reflects environmental conditions or conditions within the biofilm assemblage. Vital state was assessed by membrane integrity using LIVE/DEAD Ò BacLight TM staining kit. Samples were regularly collected in a large river, up and downstream of a large urban centre. Epilithic biomasses were similar between sites irrespective of the distinct water quality but varied temporarily, peaking up to 48 g AFDM m -2 . Bacterial community composition assessed by 16S rDNA based PCR-DGGE significantly differed between sites. Bacterial densities (median of 2.5 9 10 11 cell g AFDM -1 ) were stable whatever the sample origin or biomass. Viable bacterial fractions ranged between 13 and 83% of the total bacterial densities and were correlated with hydrological stability indicators (average of 41.9% during stable water periods, 62.4% during intermediate flow regimes and 50.0% during flow instability) and seasonal parameters. At the river section and epilithic community scales, consistent bacterial densities per unit of biomass could reflect a biofilm assemblage carrying capacity while variable membrane integrity likely integrates changes in the vital state of the community under changing environmental conditions.

Rotating disk electrodes to assess river biofilm thickness and elasticity

“…Abundances of bacteria and diatoms were monitored, showing evidence of a microbial accrual on immersed RDE surfaces. Recovered densities were comparable to those previously observed in the River Garonne biofilms for diatoms, namely 10 5 e10 7 individuals per cm 2 (Eulin, 1997) and bacteria, about 10 7 e10 8 cell per cm 2 (Lyautey et al, 2010). Temporal evolution of microbial densities of RDE biofilms fitted with measured thickness enhancement.…”

Response of biofilm-dwelling nematodes to habitat changes in the Garonne River, France: influence of hydrodynamics and microalgal availability

“…5) evidenced that a diversified group of nematode species (mainly deposit-feeding species) grew under summer conditions. It is known that summer temperatures enhance the proportion of diversified bacterial assemblages inside epilithic biofilms of the Garonne River (Boulêtreau et al, 2006;Lyautey et al, 2010). Depositfeeding nematodes can show species-specific feeding response to bacterial and cyanobacterial diversity and availability (Moens et al, 1999;Höckelmann et al, 2004;Schroeder et al, 2010).…”

“…These disturbances are recognized to shape the biomass, diversity and viability of the algal and bacterial communities inhabiting the mat (e.g. Peterson & Stevenson, 1992;Lyautey et al, 2010), implying important consequences on the functioning of biofilm processes (Cardinale, 2011).…”

Modelling epilithic biofilms combining hydrodynamics, invertebrate grazing and algal traits

“…While catastrophic detachment did not occur in this first group of growth cycles, autogenic detachment was significant. This makes sense since bacterial activity is especially intense at high temperatures recorded in the summer/autumn (Lyautey et al ., ) and can destabilise deeper biofilm layers (Boulêtreau et al ., ). Our estimation of invertebrate feeding activity was also highest for this first group of growth cycles.…”