Seite - 195 - in Freshwater Microplastics - Emerging Environmental Contaminants?

couldbe followedbymultipledisplacement amplification (MDA)3, enabling iden- tification of taxa that are metabolically active under in situ conditions. Raman spectroscopy has been combined with techniques such as fluorescence in situ hybridization (FISH), which can be used to further investigate the presence and activities of specificmicrobial taxa [92]. Fourier-transform infrared (FT-IR) spec- troscopyhas additionallybeenemployed tocharacterize thechemical composition of biofilms, providing a convenient and low-cost method for analyzingmicroor- ganisms adhering to opaquematerials [93]. Suchmethods could be used in con- junctionwith biological ratemeasurements (e.g., gas evolution) [44, 49]. This, in turn, could advance our understanding of how plastisphere taxa contribute to disease transmission, nutrient fixation, andpollutant degradation. Research intomicroplastic-associated biofilms has relied on samples thatwere collected in situ or exposed to seawater, with only a small selection of studies involving microcosm experiments under controlled conditions [21, 46, 59]. Mesocosm experiments could be used to bridge the current gap between microcosm studies and field-based research into microplastic-associated biofilms (Fig. 3).Microfluidics is also increasingly used as a tool inmicrobial ecology and couldbeemployed toobtain insights intomicrobial-microplastic interactionsunder selected conditions (e.g., in the presence of fluid flow and chemical gradients) [94, 95]. To improve our knowledge of the biodegradation of plastics and plastic- sorbed pollutants, such approaches could be supplemented by advanced surface analysis techniques. X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) have been used to investigate abiotic weathering of plastics [96–98] and could be valuable for monitoring polymer biodegradation (Fig. 3). Indeed, XPS can detect chemical signatures at the parts-per-thousand (‰) range [96], and SIMS (including nanoscale SIMS) has been used to trace microbial uptake of 13C-labeled substrates in environmental samples [99, 100].While these techniques are suitable for analyzing organic compounds, X-ray diffraction (XRD) analyses are particularly useful for measurements of inorganic materials, including metals. Although microbial interactions with plastic-associated metals (e.g., metal solubilization or precipitation) have not been previously studied, this could be achieved using XRD (e.g., see Roh et al. [101]). 4 ConcludingRemarks Over the past 5 years, several studies have improved our understanding of the taxonomy and potential activities of microbial consortia associated with microplastic particles in the environment. Due to most of these studies focusing onmarine ecosystems, there remains a particular lack of information concerning plastisphere assemblages within freshwaters. However, as highlighted in this 3Amethod for amplifyingvery lowconcentrations ofDNAfor genomic analysis. Microplastic-AssociatedBiofilms:AComparisonofFreshwater andMarine. . . 195