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Abstract Background 1,2-dichloroethane (1,2-DCA) biodegradation can occur through aerobic or anaerobic pathways that can be exploited in bioremediation strategies. Bioremediation interventions are site specific and generally based on anaerobic pathways, nevertheless expanding knowledge on proper conditions favoring the biodegradation and especially on 1,2-DCA degrading microorganisms is crucial. In this work the intrinsic biodegradation potential of an aquifer impacted by Chlorinated Aliphatic Hydrocarbons (mainly 1,2-DCA) was evaluated by characterizing the aquifer microbiome across space and time and by setting up biostimulation treatments in microcosms under different aerobic and anaerobic conditions, in parallel. Results The microbial profiling of the aquifer revealed noticeable alpha and beta diversity across the sampling sites within the aquifer and strong fluctuations over time. Surprisingly both the anaerobic and aerobic biostimulation treatments led to the successful removal of 1,2-DCA in microcosms, the enrichment of known 1,2-DCA degraders and the detection of reductive or hydrolytic dehalogenases. Ancylobacter and Starkeya were enriched in aerobic microcosms. Desulfovibrio and Desulfuromonas, known as perchloroethylene degraders, were enriched in anaerobic microcosms, suggesting they could be yet unknown 1,2-DCA respirers. Conclusions Our results demonstrate the occurrence of both aerobic and anaerobic bioremediation potential in the aquifer despite its negative redox potential. Due to the feasibility of direct oxidation with oxygen insufflation, we propose that an enhanced bioremediation strategy based on direct oxidation of 1,2-DCA could be applied to the contaminated aquifer as an ecofriendly, efficient and cost-effective approach as an alternative to anaerobic biodegradation.

Because the escalating loss of species is one of the most serious environmental crises we face, it is vital that students of biology comprehend and can communicate the roles that biodiversity plays in the functioning of ecosystems. Here, we report on a laboratory experiment that has been highly successful in our introductory biology courses at demonstrating the role of biodiversity in the productivity of ecosystems. Students created microcosms consisting of six species of phytoplankton grown separately (monocultures) and in mixtures (polycultures) in 50-mL beakers. On average, monocultures were less productive than three-species polycultures, which in turn were less productive than six-species polycultures. However, the productivity of the polycultures was generally no greater than the productivity of the most productive monocultures--a result that suggests a lack of positive ecological interactions (e.g., facilitation or niche complementarity). In contrast, there was some evidence of negative interactions among species (e.g., predation and allelopathy) that caused some polycultures to be less productive than monocultures of their constituent species. Performing this structured-inquiry experiment provided students with an opportunity to apply aspects of the scientific method in a non-trivial manner to address issues of relevance to both basic ecology principles and applied disciplines with economic significance. [For "Using Algal Microcosms in Introductory Biology Lab. I: The Influence of Nutrient Levels on the Biodiversity of an Ecological Community," see EJ1285501.]

The protection of earth's biodiversity requires a sophisticated understanding of how human activities can affect the relative abundances of species in natural ecological communities. Here, we report on an introductory biology laboratory activity in which students quantified biodiversity while investigating one of the most important controls on the biodiversity of an ecosystem: nutrient availability. Students established microcosms of six species of phytoplankton ("algae") in 50-mL beakers and exposed them to five different levels of inorganic nutrients. After two weeks, students used hemocytometers to count cells and compare the relative abundances of the algal species (i.e., their community composition) at different nutrient levels. The effect of nutrient level on biodiversity (measured by Simpson's reciprocal index) was significantly curvilinear, and best described as "U-shaped." Specifically, the algal community was most diverse at the lowest nutrient level, least diverse with a small amount of added nutrients, and intermediate in diversity at the highest nutrient levels. This convenient, quantitative investigation provided students an opportunity to consider how anthropogenic influxes of nutrients into ecosystems can lead to eutrophication, and how this phenomenon can have negative effects by decreasing the biodiversity of ecological communities. [For "Using Algal Microcosms in Introductory Biology Lab. II: The Influence of Biodiversity on Ecosystem Productivity," see EJ1285505.]

Abstract Background Rivers and streams are important components of the global carbon cycle and methane budget. However, our understanding of the microbial diversity and the metabolic pathways underpinning methylotrophic methane production in river sediments is limited. Dimethylsulfide is an important methylated compound, found in freshwater sediments. Yet, the magnitude of DMS-dependent methanogenesis nor the methanogens carrying out this process in river sediments have been explored before. This study addressed this knowledge gap in DMS-dependent methanogenesis in gravel and sandy river sediments. Results Significant methane production via DMS degradation was found in all sediment microcosms. Sandy, less permeable river sediments had higher methane yields (83 and 92%) than gravel, permeable sediments (40 and 48%). There was no significant difference between the methanogen diversity in DMS-amended gravel and sandy sediment microcosms, which Methanomethylovorans dominated. Metagenomics data analysis also showed the dominance of Methanomethylovorans and Methanosarcina. DMS-specific methyltransferase genes (mts) were found in very low relative abundances whilst the methanol-, trimethylamine- and dimethylamine-specific methyltransferase genes (mtaA, mttB and mtbB) had the highest relative abundances, suggesting their involvement in DMS-dependent methanogenesis. Conclusions This is the first study demonstrating a significant potential for DMS-dependent methanogenesis in river sediments with contrasting geologies. Methanomethylovorans were the dominant methylotrophic methanogen in all river sediment microcosms. Methyltransferases specific to methylotrophic substrates other than DMS are likely key enzymes in DMS-dependent methanogenesis, highlighting their versatility and importance in the methane cycle in freshwater sediments, which would warrant further study.

Spatial dynamics can promote persistence of strongly interacting predators and prey. Theory predicts that spatial predator-prey systems are prone to long transients, meaning that the dynamics leading to persistence or extinction manifest over hundreds of generations. Furthermore, the form and duration of transients may be altered by spatial network structure. Few empirical studies have examined the importance of transients in spatial food webs, especially in a network context, due to the difficulty in collecting the large scale and long-term data required. We examined predator-prey dynamics in protist microcosms using three experimental spatial structures: isolated, river-like dendritic networks and regular lattice networks. Densities and patterns of occupancy were followed for both predators and prey over a time scale that equates to >100 predator and >500 prey generations. We found that predators persisted in dendritic and lattice networks whereas they went extinct in the isolated treatment. The dynamics leading to predator persistence played out over long transients with three distinct phases. The transient phases showed differences between dendritic and lattice structures, as did underlying patterns of occupancy. Spatial dynamics differed among organisms in different trophic positions. Predators showed higher local persistence in more connected bottles while prey showed this in more spatially isolated ones. Predictions based on spatial patterns of connectivity derived from metapopulation theory explained predator occupancy, while prey occupancy was better explained by predator occupancy. Our results strongly support the hypothesized role of spatial dynamics in promoting persistence in food webs, but that the dynamics ultimately leading to persistence may occur with long transients which in turn may be influenced by spatial network structure and trophic interactions.

Anaerobic bioremediation is rarely an effective strategy to treat chlorinated ethenes such as trichloroethene (TCE) in acidic aquifers because partial dechlorination typically results in accumulation of daughter products. Methanotrophs have the capability of oxidizing TCE and other chlorinated volatile organic compounds (CVOCs) to non-toxic products, but their occurrence, diversity, and biodegradation capabilities in acidic environments are largely unknown. This study investigated the impacts of different methane (CH 4 ) concentrations and the presence of CVOCs on the community of acidophilic methanotrophs in microcosms prepared from acidic aquifer samples collected upgradient and downgradient of a mulch barrier installed to promote in-situ anaerobic CVOC biodegradation in Maryland, USA. The ability of indigenous methanotrophs to biodegrade CVOCs was also evaluated. Results of stable isotope probing (SIP) and Next Generation Sequencing (NGS) showed that the microbial communities in the microcosms varied by location and were affected by both CH 4 concentration and the presence of different CVOCs, many of which were biodegraded by the indigenous methanotrophs. Data indicate the likelihood of aerobic cometabolic degradation of CVOCs downgradient of the mulch barrier designed for anaerobic treatment. The study extends the overall knowledge of acidophilic methanotrophs in groundwater and shows that these bacteria have significant potential for degrading CVOCs even at low CH 4 concentrations., Competing Interests: Declarations. Conflict of interest: The authors declare no competing interests., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)