Biofilm Adhesiveness is a Reliable Proxy for the Effect Assessment of Silver Nanoparticles on the Functionality of Freshwater Biofilms

Research Article

Austin J Environ Toxicol. 2018; 4(1): 1022.

Biofilm Adhesiveness is a Reliable Proxy for the Effect Assessment of Silver Nanoparticles on the Functionality of Freshwater Biofilms

Schmidt H¹*, Gerbersdorf SU², Ullrich X², Thom M³ and Manz W¹

¹Institute for Intergrated Natural Siences, University Koblenz-Landau, Germany

²Insitute for Modelling hydraulic and Environmental Systems, University of Stuttgart, Germany

³Forschungszentrum Kμste, Leibniz Universität Hannover, Germany

*Corresponding author: Schmidt H, Department for Integrated Natural Sciences University Koblenz-Landau, Germany

Received: September 21, 2017; Accepted: January 23, 2018; Published: January 30, 2018


A sediment mesocosm was used for the cultivation of complex lotic biofilms under controlled natural-like conditions. The matured biofilms were exposed to environmentally relevant concentrations of Silver Nanoparticles (AgNPs) characterized by a variety of state of the art technologies. The aim of this study was to address the ecotoxicological damage potential of this exposure for the benthic biofilm system and associated ecosystem functions. Microbial biomass (bacteria and algae) as well as colloidal EPS protein and carbohydrate contents were assessed for a period of 18 days after the treatment. None of these parameters displayed a significant development or differences between exposed and control biofilms. However, the assessment of biofilm adhesiveness using the Mag-PI system showed highly significant effects of the exposure and was a reliable proxy for the non-lethal impact of AgNPs on the biofilm functionality. This complex sum parameter constitutes a result of various in parts still unraveled interactions within the biofilm matrix. It is precisely for this reason why The Measurement of Biofilm Adhesiveness using MagPI has to be integrated in the ecotoxicological tool box as a direct in situ method for the assessment of effects on biofilm structure and stability to influence the functionality of the overall benthic ecosystem.

Keywords: Silver Nanoparticles (Agnps); Magpi, Measurement of Biofilm Adhesiveness; Biofilm Adhesiveness; Freshwater Biofilm; EPS; Sediment Mesocosm; Biostabilization; Fine Sediments


Freshwater biofilms have great ecological relevance and are essential for aquatic habitats. The biofilm microbes not only constitute the base of the aquatic food web, the benthic pelagic feedback loop and the microbial loop make different nutrient available for other larger organisms such as makrophytes. Moreover, benthic biofilms play a significant role in the process of auto purification and can function as a trap for persistent contaminations and pollutants. Even more, during the process of biostabilization [1], benthic biofilms can significantly increase the stability of fine sediments and thus prevent a re-suspension of legacies [2-4].

Due to this variety of important ecosystem functions and an even greater number potential stressors which can impact these biofilm services, research into the reaction of benthic systems and biofilms after disturbance is increasingly expedited. As examples, the development of biofilms after an exposure to stressors such as desiccation [5,6] or antibiotics [7,8] was investigated. Furthermore, different survival strategies of biofilm microbes were studied in more detail such as morphological changes in bacteria due to stress [9] or different stages of dormancy in case of nutrient deficiency in bacteria that do not form spores [10]. There are also first insights into the resilience of the microbial community of a drinking water system and how stress can induce changes in the community composition [11]. However, reliable and measurable markers for the functionality of the biofilm system and its ecosystem services were hardly addressed. The investigation of Weaver et al. [12] assessing the resilience of the enzyme activity of ground water biofilms constitutes a suitable example of this required new comprehensive perspective as microbial enzyme activity can be essential for ground water quality and the total habitat. The adhesiveness of the biofilm constitutes another example of an essential ecosystem function: it significantly influences the development of the biofilm matrix and shapes the rate of attachment and detachment of particles and flocs [13], and thus the mass balance in the system of biofilm and fine sediment. Furthermore, the process of biostabilization is depending on biofilm stability and adhesiveness which is directly measurable using the MagPI-IP (Magnetic Particle Induction - Image Processing) [14].

First insights into the impact of different boundary conditions e.g. light intensity, flow velocity or seasonality upon microbial limnicbiostabilization could be gathered [15,16]. Furthermore, anthropogenic pollution was demonstrated to impact the ecosystem service biostabilization [2]. However, there is still a great lack of knowledge regarding the actual ecotoxicological potential of newly emerging substances. Engineered nanoparticles constitute an example for these substances emitted without profound knowledge about their fate in the environment. Generally, these industrial nanoparticles are used in the manufacturing process of a variety of different products such as textiles, cosmetics and pharmaceutics. The main reason for the addition of these nanoparticles e.g. containing titaniumdioxid, gold, copper or silver is their antimicrobial effect which should increase the shelf life and usability of the products which may result in a potential adverse effect upon limnic biofilms. Thus, research of the ecological effects of nanoparticles was focused in the DFG project “Internano” in order to assess the associated damage potential and resulting ecological thread. In this context, recent studies [17,18]. focused on Silver Nanoparticles (AgNPs) as they have a major fraction of all manufactured and used nanoparticles: it could be demonstrated that even an exposure to a sub-lethal concentration of AgNPs significantly impacted the structure and stability of model freshwater biofilms.

This study aimed to broaden the gathered knowledge about the effects of AgNPs upon the functionality of freshwater biofilms. In contrast to the aforementioned investigations, natural complex biofilms were analyzed in order to increase the ecological validity of the results. Furthermore, the short term as well as the long term development of the biofilms after an exposure to different concentrations of AgNPs was assessed. In doing so, a central question was how the adhesiveness of the biofilm isaffected by the exposure to AgNPs. There are two reasons why this parameter was assessed in an extensive measurement campaign to evaluate its suitability as an indicator for ecological stress: firstly, the reliability of biofilm adhesiveness as a marker for biofilm stability and biostabilization could be shown recently [15]. Secondly, its sensitivity to other adverse effects such as Triclosan [19], was previously demonstrated. Furthermore, if there is a measurable reaction in the microbial biostabilization capacity of the analyzed biofilms, the determination of biofilm adhesiveness could constitute new and essential straight forward tool for future risk assessment as well as monitoring and sediment management strategies.

Material and Methods

Experimental setup

Natural biofilms were cultivated in a setup consisting of two independent mesocosms (length x width x height: 0,70 x 0,25 x 0,16 m each; (Figure 1) with individual water reservoir and water circulation. 50Liters of fluvial water and suspended sediment gathered from the river Enz (Roßwag, Baden-Wμrttemberg, Germany) were transferred into each flume/ reservoir tank. A pump (380 Bilge Pump 380 GPH, PENTAIR, Herentals, Belgium) with a flow rate of 1438 l h-1ensured a constant water circulation through the flume of each mesocosm. Thus, the floating microbial community developed as biofilm on the provided substrate (inert glass beads, diameter 150-200 μm) which was filled in 32 rectangular cartridges (length x width x height: 0.08 m x 0.06 m x 0.02 m). The illumination was set using daylight fluorescence tubes (OsramBiolux; 480 - 665 nm) in a day-night rhythm of 10/14 h illumination/darkness.