Impairment of the Bacterial Biofilm Stability by Triclosan

Abstract

The accumulation of the widely-used antibacterial and antifungal compound triclosan (TCS) in freshwaters raises concerns about the impact of this harmful chemical on the biofilms that are the dominant life style of microorganisms in aquatic systems. However, investigations to-date rarely go beyond effects at the cellular, physiological or morphological level. The present paper focuses on bacterial biofilms addressing the possible chemical impairment of their functionality, while also examining their substratum stabilization potential as one example of an important ecosystem service. The development of a bacterial assemblage of natural composition – isolated from sediments of the Eden Estuary (Scotland, UK) – on non-cohesive glass beads (<63 µm) and exposed to a range of triclosan concentrations (control, 2 – 100 µg L−1) was monitored over time by Magnetic Particle Induction (MagPI). In parallel, bacterial cell numbers, division rate, community composition (DGGE) and EPS (extracellular polymeric substances: carbohydrates and proteins) secretion were determined. While the triclosan exposure did not prevent bacterial settlement, biofilm development was increasingly inhibited by increasing TCS levels. The surface binding capacity (MagPI) of the assemblages was positively correlated to the microbial secreted EPS matrix. The EPS concentrations and composition (quantity and quality) were closely linked to bacterial growth, which was affected by enhanced TCS exposure. Furthermore, TCS induced significant changes in bacterial community composition as well as a significant decrease in bacterial diversity. The impairment of the stabilization potential of bacterial biofilm under even low, environmentally relevant TCS levels is of concern since the resistance of sediments to erosive forces has large implications for the dynamics of sediments and associated pollutant dispersal. In addition, the surface adhesive capacity of the biofilm acts as a sensitive measure of ecosystem effects.

Effects of a chronic lower range of triclosan exposure on a stream mesocosm community

“…Of prime speculation has been the potential for cascading ecological consequences for stream communities, given demonstrated biofilm-specific effects [22,27,29,31]. Our results equally demonstrated changes in the biofilm community, in terms of bacterial cell density, algal biomass, and algal structure (decreased cyanobacteria densities, potential change in diatom species).…”

“…The hypothesis follows that triclosan may be impacting whole ecosystems from ecological cascades, if the basal producers and osmotrophs of streams are sensitive. Several studies have assessed potential effects of triclosan at higher levels of ecological organization, focusing on understanding whether interacting structural and functional changes occur with exposure in river biofilms (also termed periphyton) [22,[26][27][28][29][30][31]. Generally, it can be concluded from these studies that triclosan at relatively low concentrations ( 10 mg/L) could significantly alter periphyton structure and activity.…”

Resilience and recovery: The effect of triclosan exposure timing during development, on the structure and function of river biofilm communities

“…The DGGE results pointing to a change in community structure are also consistent with both toxic and selective TCS effects. The findings of Drury et al (2013) (8 g g −1 ) and Lubarsky et al (2012) (2-100 g l −1 ) also show that chronic TCS exposure resulted in changes in bacterial community composition and a loss of diversity. Such changes may be due to selective recruitment or inhibition of sensitive species during biofilm development.…”

“…In fact, Schreiber and Szewzyk (2008) reported that even nanogram per liter of antimicrobials significantly affected the recruitment of bacteria to the attached community. In contrast, Lubarsky et al (2012) suggested that while surface recruitment was not affected by TCS, biofilm development was inhibited by increasing TCS levels. Morin et al (2010a), utilized in situ incubations to examine effects of pesticides used in vineyards and reported that biofilm dry weight, ash free dry weight, and Chl-a suggested that biofilms translocated to contaminant free sites recovered within two months.…”

Seasonal variations of the composition of microbial biofilms in sandy tidal flats: Focus of fatty acids, pigments and exopolymers

“…Additionally, they are sensitive to anthropic actions such as eutrophication or antibiotic release in the environment (Lubarsky et al, 2012;Sawall et al, 2012). These biofilms are often very productive and they also provide different ecosystem services, such as nutrient recycling, degradation of pollutants and sediment stabilisation, and they are essential for the recruitment of numerous benthic organisms (Decho, 2000).…”