Structural and functional recovery of microbial biofilms after a decrease in copper exposure: Influence of the presence of pristine communities

Abstract

The present study aimed at assessing the recovery of phototrophic and heterotrophic biofilm communities after a decrease in copper exposure. An original experiment was designed to evaluate the possible influence of non-exposed (i.e. pristine) communities (e.g. via immigration processes) in recovery dynamics. Laboratory channels were used to study the structural and functional changes in microbial communities after a 4-week Cu exposure period in the presence and absence of pristine biofilms. When pristine biofilms were present, phototrophic communities recovered within 6 weeks, both in terms of biomass, structure and photosynthetic activity. Recovery processes were also detected using the PICT approach. In contrast, in the absence of pristine communities, all of the Cu-induced changes recorded in the phototrophic communities remained throughout the recovery period.Regardless of the presence or absence of pristine biofilms, the decrease in Cu exposure did not abolish Cu-induced changes in bacterial community structure, whereas functional recovery (based on beta-glucosidase activity) was complete in both recovery contexts.These results revealed that microbial community response to a decrease in Cu exposure differs between phototrophic and heterotrophic communities. The presence of pristine communities greatly influences the structural and functional recovery of phototrophic communities, suggesting an important role of microbial immigration processes, but have far less influence on the recovery trajectory of heterotrophic communities. Highlights► We tested the influence of microbial immigration in biofilm recovery after a Cu exposure.► Recovery dynamics differed between phototrophic and heterotrophic communities.► Microbial immigration enhanced the recovery of phototrophic communities.► Heterotrophic community recovery slightly depended on microbial immigration processes.

Diatom immigration drives biofilm recovery after chronic copper exposure

“…Figure 3 indicates that 2 weeks were more than enough for ExCu1 assemblages to attain structure similar to the Controls, in accordance with the most optimistic in situ translocation scenarios (Tolcach & Gó mez, 2002). Cu concentration in the biofilm) as in ExCu1 (Lambert et al, 2012), thus maintaining somewhat greater toxic pressure. It followed a trajectory that was probably driven by in situ differential reproduction of species selected by previous Cu exposure and subsequently favoured by the new (uncontaminated) environmental conditions.…”

“…The slower increase in periphytic biomass in ExCu2 channels did not lead to such a strong decrease in local contamination (i.e. Cu concentration in the biofilm) as in ExCu1 (Lambert et al, 2012), thus maintaining somewhat greater toxic pressure. This could explain why the succession trajectory of ExCu2 assemblages were mainly driven by a massive growth of Achnanthidium minutissimum, a pioneer species (Stevenson, 1990;Medley & Clements, 1998) that is known to cope with metal contaminations and to the decline of the copper-tolerant Nitzschia hantzschiana, which is probably less competitive than other species when water contamination ceases.…”

“…These channels were arranged in a blocked design into four sets of triplicate channels, two of which were grown under control conditions (see details in Lambert et al, 2012) while the other two were supplemented with copper at about 20 lg L )1 for 4 weeks to obtain mature biofilms before the experiment. These channels were arranged in a blocked design into four sets of triplicate channels, two of which were grown under control conditions (see details in Lambert et al, 2012) while the other two were supplemented with copper at about 20 lg L )1 for 4 weeks to obtain mature biofilms before the experiment.…”

“…A suspension of natural biofilm from a pristine site located upstream of any pollution inputs in the Morcille river (Beaujolais region, Eastern France) was inoculated into 12 laboratory channels (l · w · d = 63 · 11 · 4 cm). These channels were arranged in a blocked design into four sets of triplicate channels, two of which were grown under control conditions (see details in Lambert et al, 2012) while the other two were supplemented with copper at about 20 lg L )1 for 4 weeks to obtain mature biofilms before the experiment. The channels were placed in parallel, at a light intensity of approximately 3500 lux (13:11 light ⁄ dark regime), under continuous water flow in recirculating mode (centrifugal pumps Rena Flow 600, 1.2 L min )1 ).…”

Substratum‐Associated Microbiota

“…Recovery of phototrophic and heterotrophic biofilm assemblages from copper (Cu) exposure differed between phototrophic and heterotrophic assemblages. The presence of pristine assemblages greatly influenced the structural and functional recovery of phototrophic assemblages, but had far less influence on the recovery trajectory of heterotrophic assemblages (Lambert et al, 2012 Tropic Interactions. Bacteria are an important part of aquatic food webs in part because they can transfer organic carbon to higher tropic levels.…”