Neutral mechanisms and niche differentiation in steady-state insular microbial communities revealed by single cell analysis.

In completely insular microbial communities, evolution of community structure cannot be shaped by the immigration of new members. In addition, when those communities are run in steady state, the influence of environmental factors on their assembly is reduced. Therefore, one would expect similar community structures under steady-state conditions. Yet, in parallel setups, variability does occur. To reveal ecological mechanisms behind this phenomenon, five parallel reactors were studied at the single-cell level for about 100 generations and community structure variations were quantified by ecological measures. Whether community variability can be controlled was tested by implementing soft temperature stressors as potential synchronizers. The low slope of the lognormal rank-order abundance curves indicated a predominance of neutral mechanisms, i.e., where species identity plays no role. Variations in abundance ranks of subcommunities and increase in inter-community pairwise ß-diversity over time support this. Niche differentiation was also observed, as indicated by steeper geometric-like rank-order abundance curves and increased numbers of correlations between abiotic and biotic parameters during initial adaptation and after disturbances. Still, neutral forces dominated community assembly. Our findings suggest that complex microbial communities in insular steady-state environments can be difficult to synchronize and maintained in their original or desired structure, as they are non-equilibrium systems.

A framework for P-cycle assessment in wastewater treatment plants.

Phosphorus (P) in wastewater has a variety of negative effects and is usually permanently lost as a non-renewable resource. To mitigate future P shortage, P must be recovered from wastewater, preferably by bio-based technologies to avoid toxic side streams. A standardized procedure for the determination of P types and P concentrations in all liquid and solid process stages was established, which is applicable to all full-scale wastewater treatment plants (WWTPs). Based on this, an equally universal calculation framework for P-cycle assessment based on volume flow and mass load rates was designed to identify the most promising process streams for biological P recovery. As an example, in 16 process streams of a typical WWTP, concentrations of free, bound and total P were calculated and microbial communities were analyzed by flow cytometry over 748 days. The most promising process streams for the recovery of free P were anaerobic digester sludge, centrate and the water-extracts of the biosolids with 0.510 kg P m-3, 0.075 kg P m-3 and 1.023 kg P m-3, while the best process streams for the recovery of bound P were return sludge, excess sludge, anaerobic digester sludge, and the solids of the biosolids with 0.300 kg P m-3, 0.268 kg P m-3, 0.213 kg P m-3 and 1.336 kg P m-3, respectively. Microorganisms capable of P accumulation were active in all process stages and it was observed that chemical P precipitation antagonizes biological P removal. The framework for P-cycle assessment was able to identify process streams that are economically viable to make future in-stream technologies for biological P removal feasible.

The Impact of the Antibiotic Fosfomycin on Wastewater Communities Measured by Flow Cytometry.

Fosfomycin is a re-emergent antibiotic known to be effective against severe bacterial infections even when other antibiotics fail. To avoid overuse and thus the risk of new antibiotic resistance, the European Commission has recommended the intravenous use of fosfomycin only when other antibiotic treatments fail. A release of fosfomycin into the environment via wastewater from not only municipalities but also already from the producing pharmaceutical industry can seriously undermine a sustaining therapeutic value. We showed in long-term continuous-mode bioreactor cultivation and by using microbial community flow cytometry, microbial community ecology tools, and cell sorting that the micro-pollutant altered the bacterial wastewater community (WWC) composition within only a few generations. Under these conditions, fosfomycin was not readily degraded both at lower and higher concentrations. At the same time, operational reactor parameters and typical diversity parameters such as α- and intracommunity ß-diversity did not point to system changes. Nevertheless, an intrinsic compositional change occurred, caused by a turnover process in which higher concentrations of fosfomycin selected for organisms known to frequently harbor antibiotic resistance genes. A gfp-labeled Pseudomonas putida strain, used as the model organism and a possible future chassis for fosfomycin degradation pathways, was augmented and outcompeted in all tested situations. The results suggest that WWCs, as complex communities, may tolerate fosfomycin for a time, but selection for cell types that may develop resistance is very likely. The approach presented allows very rapid assessment and visualization of the impact of antibiotics on natural or managed microbial communities in general and on individual members of these communities in particular.