Effluents from wastewater treatment plants (WWTPs) containing micro-organisms and residual nitrogen can stimulate nitrification in freshwater streams. We hypothesized that different ammonia-oxidizing (AOB) and nitrite-oxidizing (NOB) bacteria present in WWTP effluents differ in their potential to colonize biofilms in the receiving streams. In an experimental approach, we monitored biofilm colonization by nitrifiers in ammonium- or nitrite-fed microcosm flumes after inoculation with activated sludge. In a field study, we compared the nitrifier communities in a full-scale WWTP and in epilithic biofilms downstream of the WWTP outlet. Despite substantially different ammonia concentrations in the microcosms and the stream, the same nitrifiers were detected by fluorescence in situ hybridization in all biofilms. Of the diverse nitrifiers present in the WWTPs, only AOB of the Nitrosomonas oligotropha/ureae lineage and NOB of Nitrospira sublineage I colonized the natural biofilms. Analysis of the amoA gene encoding the alpha subunit of ammonia monooxygenase of AOB revealed seven identical amoA sequence types. Six of these affiliated with the N. oligotropha/ureae lineage and were shared between the WWTP and the stream biofilms, but the other shared sequence type grouped with the N. europaea/eutropha and N. communis lineage. Measured nitrification activities were high in the microcosms and the stream. Our results show that nitrifiers from WWTPs can colonize freshwater biofilms and confirm that WWTP-affected streams are hot spots of nitrification.

Massive biofilms have been discovered in the cave of an iodine-rich former medicinal spring in southern Germany. The biofilms completely cover the walls and ceilings of the cave, giving rise to speculations about their metabolism. Here we report on first insights into the structure and function of the biofilm microbiota, combining geochemical, imaging and molecular analytics. Stable isotope analysis indicated that thermogenic methane emerging into the cave served as an important driver of biofilm formation. The undisturbed cavern atmosphere contained up to 3000 p.p.m. methane and was microoxic. A high abundance and diversity of aerobic methanotrophs primarily within the Methylococcales (Gammaproteobacteria) and methylotrophic Methylophilaceae (Betaproteobacteria) were found in the biofilms, along with a surprising diversity of associated heterotrophic bacteria. The highest methane oxidation potentials were measured for submerged biofilms on the cavern wall. Highly organized globular structures of the biofilm matrix were revealed by fluorescent lectin staining. We propose that the extracellular matrix served not only as an electron sink for nutrient-limited biofilm methylotrophs but potentially also as a diffusive barrier against volatilized iodine species. Possible links between carbon and iodine cycling in this peculiar habitat are discussed.

Dispersal and colonization are important for the assembly and biodiversity of microbial communities. While emigration as the initial step of dispersal has become increasingly understood in model bacterial biofilms, the drivers of dispersal and colonization in complex biofilms remain elusive. We grew complex biofilms in microcosms from natural surface water in laminar and turbulent flow, and investigated dispersal and colonization patterns of fluorescently labeled cells and microbeads in nascent and mature biofilms. Settling occurred in nonrandom spatial patterns governed by the interplay of local flow patterns and biofilm topography. Settling was higher in treatments with nascent biofilms, with fewer cells remaining in the water column than in treatments with mature biofilms. The flow regime had no effect on settling velocity, even though in mature biofilms the formation of streamers under turbulent flow enhanced particle trapping compared with the laminar flow treatment. Hence, small-scale variations in the flow pattern seemed to be more important than the overall flow regime. Furthermore, spatial analysis of the colonizer patterns suggests that bacteria have moved in the biofilm after settling. Our results show that colonization of biofilms in a model stream environment is a heterogeneous process differently affected by biological and physical factors.

Climate change has a massive impact on the global water cycle. Subsurface ecosystems, the earth largest reservoir of liquid freshwater, currently experience a significant increase in temperature and serious consequences from extreme hydrological events. Extended droughts as well as heavy rains and floods have measurable impacts on groundwater quality and availability. In addition, the growing water demand puts increasing pressure on the already vulnerable groundwater ecosystems. Global change induces undesired dynamics in the typically nutrient and energy poor aquifers that are home to a diverse and specialized microbiome and fauna. Current and future changes in subsurface environmental conditions, without doubt, alter the composition of communities, as well as important ecosystem functions, for instance the cycling of elements such as carbon and nitrogen. A key role is played by the microbes. Understanding the interplay of biotic and abiotic drivers in subterranean ecosystems is required to anticipate future effects of climate change on groundwater resources and habitats. This review summarizes potential threats to groundwater ecosystems with emphasis on climate change and the microbial world down below our feet in the water saturated subsurface. caister.com/cimb 509 Curr. Issues Mol. Biol. Vol. 41 Climate Change and Groundwater Microbes Retter et al. use (e.g. cooling agent), as well as for production of potable water. Worth mentioning, in Europe, around 50 -70 % of all drinking water stems from groundwater (Zektser and Everett, 2004). Groundwater constitutes a major component of the hydrological cycle and sustains streams, lakes, and wetlands, many of which would not be perennial without the direct connection to an aquifer. Groundwater ecosystems are typically covered by vegetated soil and vadose sediment layers of varying thickness.Where the protective layers are thin and perforated (e.g. in mountainous areas and karstic rock) or even absent, and where groundwater reaches land surface (e.g.wetlands and springs), the down below systems are highly vulnerable to disturbance from above. Moreover, due to the comparably long residence time of groundwater in the subsurface (Danielopol et al., 2003), its response time to external impacts can be delayed and sometimes masked by complex hydrologically patterns (Alley et al., 2002;Kløve et al., 2014). The subsurface is a naturally light deprived and nutrient limited environment, hence the energy required for sustaining groundwater ecosystems is largely derived from the surface. In fact, the groundwater ecosystems balance is susceptible to several external influences. It is on one hand largely dependent on energy import from the surface, but on the other hand responding sensitively to increased input of organics and nutrients as well as various types of contaminants including heavy metals and heat. While in the past, groundwater pollution mainly resulted from source contaminations with deposited or spilled petroleum hydrocarbons and halogenated solvents as well as leaking...