Search Results (41)

The availability of detritus is a key factor influencing aquatic biota and can significantly affect decomposition processes. In this study, we investigated how varying quantities of surrounding detritus impact leaf litter decay rates. It was tested in flowing and still-water microcosms to highlight context-dependent effects of surrounding detritus on leaf litter decomposition. To isolate the effect of detritus amount, experiments were conducted in laboratory microcosms simulating lotic and lentic ecosystems, each containing leaf fragments for decomposition assessments. Four detritus quantities were tested, with invertebrates either allowed or restricted from moving among detritus patches. Leaf decomposition rates were influenced by the amount of surrounding detritus, with slower decay observed at higher detritus conditions, regardless of invertebrate mobility. Detritivore distribution responded to both detritus quantity and oxygen availability, showing a preference for high detritus conditions. Additionally, detritus quantity affected microbial activity with a quadratic response, as indicated by leaf respiration rates. Overall, our findings indicate that the amount of surrounding detritus modulates leaf litter decomposition independently of invertebrate density, by influencing oxygen dynamics and, consequently, the activity of biological decomposers. Full article

Glyphosate based-herbicides are stressors of great concern because they can impact aquatic ecosystems. Similarly, lithium, a metal, is currently of concern because of its increasing use worldwide. Because glyphosate-based herbicides and lithium might co-occur in aquatic environments, there is a need to assess their impacts on aquatic organisms, such as aquatic fungi, as they play a key role in plant litter decomposition in streams. Microcosm assays were used to examine the effects of lithium and the herbicide isopropylammonium glyphosate (IPAG), alone or in mixtures, on microbial leaf mass loss, total fungal sporulation and biomass production. IPAG (alone and combined with LiCl) neither affected plant litter decomposition nor fungal biomass production, but boosted total fungal sporulation. Dimorphospora foliicola, the most tolerant species among the twelfth leaf inhabitant fungal species, is the major contributor to total fungal sporulation. IPAG interacts with LiCl in the total fungal sporulation and sporulation of D. foliicola, A. tetracladia, and F. curvula, indicating a species dependent-effect. IPAG alone or combined with LiCl greatly decreased the diversity of spores, as did as LiCl alone, but to a lesser extent. Finally, aquatic fungal communities reveal redundancy and resiliency to IPAG and LiCL, maintaining the health of aquatic ecosystems. Full article

At present, studies on hydrophyte periphytic biofilm have mainly focused on natural water bodies or low-strength wastewater due to the inability of most plants to grow in high-strength wastewater. Therefore, the formation process and characteristics of plant periphytic biofilm growing in high-strength wastewater are still unclear. Based on the microcosm experiment, the formation process and characteristics of two kinds of plants (Myriophyllum elatinoides (Me) and Pontederia cordata (Pc)) periphytic biofilms were investigated with changes in water quality. The periphytic biofilm weight (BW) of Me and Pc reached equilibrium at 21 days, while the BW of Me was higher than that of Pc under high-load conditions (total nitrogen (TN) concentration ≥ 104.0 mg/L). When the TN concentration was 201.7 mg/L, the highest BW of Me was 0.99 mg/cm². In addition, the structural complexity of hydrophyte periphytic biofilm was higher under TN concentrations ≥ 70.9 mg/L than that under TN concentrations ≤ 56.9 mg/L. N concentration and environmental factors could affect periphytic BW and biofilm Chlorophyll a (Chla.). Through linear regression fitting, it was found that periphytic BW and biofilm Chla. were positively correlated with the concentrations of NH₄⁺-N and TN in water, while they were negatively correlated with the concentration of NO₃⁻-N. Random Forest results showed that NO₃⁻-N concentration had an important effect on hydrophyte periphytic BW. The results of this study provided a new understanding of the formation process and characteristics of aquatic plant periphytic biofilm under high-strength conditions and a prospect for sustainable development in the treatment of high-strength wastewater. Full article

The objective of the present study was to isolate endophytes from the roots of the halophyte Sesuvium portulacastrum, which is applied for aquatic phytoremediation. From these endophytes, siderophore-producing bacteria were specifically isolated for their potential capacity to promote plant growth. The siderophore production capacity of the isolated bacteria was quantified, and a high-yield siderophore-producing strain was selected for further investigation. A total of 33 endophytic bacteria were successfully isolated and identified using a culturable approach. Of these, 10 siderophore-producing bacteria were identified using the selective agar assay, displaying siderophore unit (SU) values ranging from 11.90% to 80.39%. It is noteworthy that Erwinia sp. QZ-E9 exhibited the highest siderophore production capacity, achieving an SU of 80.39%. A microcosm co-cultivation experiment was conducted with the strain QZ-E9 in iron-deficient conditions (2 μmol/L Fe³⁺). The results demonstrated that strain QZ-E9 significantly enhanced the growth of S. portulacastrum, by increases in both fresh weight (1.41 g) and root length (18.7 cm). Furthermore, fluorescence in situ hybridization (FISH) was utilized to ascertain the colonization pattern of strain QZ-E9 within the plant roots. The analysis demonstrated that strain QZ-E9 exhibited extensive colonization of the epidermal and outer cortical cells of S. portulacastrum roots, as well as the intercellular spaces and vascular tissues. This colonization indicated that Erwinia sp. QZ-E9 plays a crucial role in promoting the growth of S. portulacastrum, presumably through its siderophore-mediated iron acquisition mechanism. Full article

The propagation of antibiotic resistance in environments, particularly aquatic environments that serve as primary pathways for antibiotic resistance genes (ARGs), poses significant health risks. The impact of nutrients, as key determinants of bacterial growth and metabolism, on the propagation of ARGs, particularly extracellular ARGs (eARGs), remains poorly understood. In this study, we collected microorganisms from the Yangtze River and established a series of microcosms to investigate how variations in nutrient levels and delivery frequency affect the relative abundance of intracellular ARGs (iARGs) and eARGs in bacterial communities. Our results show that the relative abundance of 7 out of 11 representative eARGs in water exceeds that of iARGs, while 8 iARGs dominate in biofilms. Notably, iARGs and eARGs consistently exhibited opposite responses to nutrient variation. When nutrient levels increased, iARGs in the water also increased, with the polluted group (COD = 333.3 mg/L, COD:N:P = 100:3:0.6, m/m) and the eutrophic group (COD = 100 mg/L, COD:N:P = 100:25:5, m/m) showing 1.2 and 3.2 times higher levels than the normal group (COD = 100 mg/L, COD:N:P = 100:10:2, m/m), respectively. In contrast, eARGs decreased by 6.7% and 8.4% in these groups. On the other hand, in biofilms, higher nutrient levels led to an increase in eARGs by 1.5 and 1.7 times, while iARGs decreased by 17.5% and 50.1% in the polluted and eutrophic groups compared to the normal group. Moreover, while increasing the frequency of nutrient delivery (from 1 time/10 d to 20 times/10 d) generally did not favor iARGs in either water or biofilm, it selectively enhanced eARGs in both. To further understand these dynamics, we developed an ARGs-nutrient model by integrating the Lotka–Volterra and Monod equations. The results highlight the complex interplay of bacterial growth, nutrient availability, and mechanisms such as horizontal gene transfer and secretion influencing ARGs’ propagation, driving the opposite trend between these two forms of ARGs. This contrasting response between iARGs and eARGs contributes to a dynamic balance that stabilizes bacterial resistance levels amid nutrient fluctuations. This study offers helpful implications regarding the persistence of bacterial resistance in the environment. Full article

This study investigates the combined effect of microplastics and cadmium on the decomposition of litter, the structure of fungal communities, and the feeding behavior of invertebrates in an aquatic ecosystem. Through a series of microcosm experiments, we demonstrate that exposure to MPs and Cd significantly reduced the decomposition of leaf litter. Notably, the cumulative impact of combined MP and Cd exposure was found to be greater than their individual effects. During this process, the carbon–nitrogen ratio of the litter increased, while dehydrogenase activity and fungal biomass were inhibited. Additionally, the relative abundance of Ascomycota and Basidiomycota fungi decreased, weakening their role in the decomposition of leaf litter. Conversely, MPs and Cd reduced the relative content of leaf litter lignin, improving its quality as food, thereby leading to an increase in the feeding rate of invertebrates. This dual effect indicates that micropollutants suppress the decomposition of litter by regulating microbial metabolic activity and fungal community structure but promote invertebrate feeding. Our findings provide crucial insights into the adverse effects of MPs and Cd on the structure and diversity of aquatic fungal communities, which could have long-term impacts on the food webs and nutrient cycling progress of aquatic ecosystems. Full article

The illegal activity of gold mining in the Brazilian Pantanal is contaminating the aquatic ecosystem with mercury. This contamination has been potentiated by mercury methylation due to a typical natural phenomenon of the Pantanal ecosystem known as “dequada”. The present study estimated in the laboratory the temporal production of methylmercury at two timepoints: the beginning of a flood, when the “dequada” phenomenon occurs, and the dry season without such phenomenon. After collecting water and sediment, experiments were performed with microcosms to reproduce conditions close to nature. To monitor the concentration of methylmercury, 1.0 mg L⁻¹ of Hg²⁺ was added to water and sediment experiments in the Castelo and Saracura bays, both during the “dequada” and without it; monitoring lasted for 25 days. The methylmercury concentration was analyzed using atomic fluorescence spectrometry, total organic carbon using TOC 5000A, and physical and chemical parameters such as pH, redox potential, and dissolved oxygen with a multi-parameter probe. The results led to the conclusion that the “dequada” phenomenon significantly affected mercury methylation, because the environmental changes caused by this phenomenon such as the increased concentration of organic matter, decreased dissolved oxygen, and decreased pH, potentiated mercury methylation. During the “dequada” in the Castelo bay, the methylation rate was 3.5 times higher (6297.56 ng L⁻¹) than in the experiment without the “dequada” (1827.44 ng L⁻¹). Therefore, the gold mining activity in Pantanal can cause great damage to the ecosystem because this environment favors mercury methylation, making its most toxic form active in the aquatic ecosystem of Pantanal. Full article

Plastic debris is a growing threat in freshwater ecosystems and transport models predict that many plastics will sink to the benthos. Among the most common plastics found in the Laurentian Great Lakes sediments are polyethylene terephthalate (especially fibers; PET), polyvinylchloride (particles; PVC), and styrene-butadiene rubber resulting from tire wear (“crumb rubber”; SBR). These materials vary substantially in physical and chemical properties, and their impacts on benthic biogeochemistry and microbial community structure and function are largely unknown. We used a microcosm approach to evaluate the impact of these three plastics on benthic-pelagic coupling, sediment properties, and sediment microbial community structure and function using sediments from Irondequoit Bay, a major embayment of Lake Ontario in Rochester, New York, USA. Benthic metabolism and nitrogen and phosphorous cycling were all uniquely impacted by the different polymers. PET fibers and PVC particles demonstrated the most unique effects, with decreased ecosystem metabolism in sediments containing PET and greater nutrient uptake in sediments with PVC. Microbial diversity was reduced in all treatments containing plastic, but SBR had the most substantial impact on microbial community function, increasing the relative importance of metabolic pathways such as hydrocarbon degradation and sulfur metabolism. Our results suggest that individual polymers have unique impacts on the benthos, with divergent implications for ecosystem function. This provides deeper insight into the myriad ways plastic pollution may impact aquatic ecosystems and will help to inform risk assessment and policy interventions by highlighting which materials pose the greatest risk. Full article

Microbial respiration determines the accumulation of reduced solutes and negative redox potential in organic sediments, favoring the mobilization of dissolved inorganic phosphorus (DIP), generally coprecipitated with Fe oxyhydroxides. Macrophytes releasing oxygen from the roots can contrast DIP mobility via the oxidation of anaerobic metabolism end-products. In this work, the submerged macrophyte Vallisneria spiralis was transplanted into laboratory microcosms containing sieved and homogenized organic sediments collected from a contaminated wetland. Sediments with and without plants were incubated under light and dark conditions for oxygen and DIP fluxes measurements and pore water characterization (pH, oxidation-reduction potential, DIP, dissolved Mn, and Fe). Bare sediments were net DIP sources whereas sediments with V. spiralis were weak DIP sources in the dark and large sinks in light. V. spiralis radial oxygen loss led to less negative redox potential and lower Fe, Mn, and DIP concentrations in pore water. Roots were coated by reddish plaques with large amounts of Fe, Mn, and P, exceeding internal content. The results demonstrated that at laboratory scale, the transplant of V. spiralis into polluted organic sediments, mitigates the mobility of DIP and metals through both direct and indirect effects. This, in turn, may favor sediment colonization by less-tolerant aquatic plants. Further in situ investigations, coupled with economic analyses, can evaluate this potential application as a nature-based solution to contrast eutrophication. Full article

Florfenicol is one of the most widely used antibiotics in aquaculture and veterinary clinics because of its low side effects and strong bactericidal effect. A total of 45~60% of florfenicol is not absorbed by the animal body and accumulates in the aquatic environment through a variety of pathways, which affects denitrification. Indoor aquatic microcosm models were constructed and sediment samples were collected at different florfenicol concentrations (0.1, 1, 10, and 100 mg/L) on days 0, 7, 30, and 60 to extract the microbial genome DNA and determine the water properties. qPCR and amplicon sequencing were used to study the dynamic changes in the nirS gene and nirS-type denitrification community structure, diversity, and abundance, respectively. The results showed that high florfenicol stress influenced the sediment’s physicochemical properties, reducing conductivity, alkaline dissolved nitrogen, and organic matter content. In addition, the abundance of nirS, a functional denitrification gene, increased obviously with increased florfenicol concentrations but decreased the diversity of nirS-type denitrification microorganisms. Proteobacteria was the dominant denitrifying phylum in the sediment. Our study provides a scientific basis for the rational use of florfenicol in aquaculture to maintain a healthy and stable microecological environment and also provides a preliminary understanding of the response characteristics of water denitrifying microorganisms to florfenicol exposure. Full article

Textile waste contributes to the pollution of both terrestrial and aquatic ecosystems. While natural textile fibres are known to be biodegraded by microbes, the vast majority of textiles now contain a mixture of processed plant-derived polymers and synthetic materials generated from petroleum and are commonly dyed with azo dyes. This presents a complex recycling problem as the separation of threads and removal of dye are challenging and costly. As a result, the majority of textile waste is sent to landfill or incinerated. This project sought to assess the potential of fungal bioremediation of textile-based dye as a step towards sustainable and environmentally-friendly means of disposal of textile waste. Successful development of an agar-independent microcosm enabled the assessment of the ability of two fungal species to grow on a range of textiles containing an increasing percentage of elastane. The white rot fungus Hypholoma fasciculare was shown to grow well on semi-synthetic textiles, and for the first time, bioremediation of dye from textiles was demonstrated. Volatile analysis enabled preliminary assessment of the safety profile of this process and showed that industrial scale-up may require consideration of volatile capture in the design process. This study is the first to address the potential of fungi as bioremediation agents for solid textile waste, and the results suggest this is an avenue worthy of further exploration. Full article

Non-steroidal anti-inflammatory drugs (NSAIDs) are increasingly recognized as potential environmental contaminants that may induce toxicity in aquatic ecosystems. This 3-week microcosm experiment explores the acute impacts of NSAIDs, including diclofenac (DCF), ibuprofen (IBU), and acetylsalicylic acid (ASA), on bacterial communities using a wide range of these substances (200–6000 ppm). The results showed that the NSAID-treated microcosms had higher cell count values than control samples, though the diversity of microbial communities decreased. The isolated heterotrophic bacteria mostly belonged to Proteobacteria, particularly Klebsiella. Next-generation sequencing (NGS) revealed that NSAIDs altered the structure of the bacterial community composition, with the proportion of Proteobacteria aligning with the selective cultivation results. Bacteria had higher resistance to IBU/ASA than to DCF. In DCF-treated microcosms, there has been a high reduction of the number of Bacteroidetes, whereas in the microcosms treated with IBU/ASA, they have remained abundant. The numbers of Patescibacteria and Actinobacteria have decreased across all NSAID-treated microcosms. Verrucomicrobia and Planctomycetes have tolerated all NSAIDs, even DCF. Cyanobacteria have also demonstrated tolerance to IBU/ASA treatment in the microcosms. The archaeal community structure was also impacted by the NSAID treatments, with Thaumarchaeota abundant in all microcosms, especially DCF-treated microcosms, while Nanoarchaeota is more typical of IBU/ASA-treated microcosms with lower NSAID concentrations. These results indicate that the presence of NSAIDs in aquatic environments could lead to changes in the composition of microbial communities. Full article

The eutrophication of aquatic systems is a problem related to the contribution of excess nutrients—phosphorus (P) and nitrogen (N)—to water bodies, which produces an increase in cyanobacterial blooms. Under eutrophic conditions, P and N concentrations are sufficient for cyanobacteria growth, and some micronutrients are considered to become limiting for population growth. This work aimed to assess the effect of iron on cyanobacteria growth and the content of MCs in natural populations of Microcystis spp. Microcosm setting experiments were carried out with natural samples collected during two bloom events of Microcystis spp., kept under controlled light, temperature and pH conditions. The first bloom sample was exposed to different iron concentrations (400, 700 and 1100 µg Fe·L⁻¹) to determine the optimum concentration for growth. The second was exposed to different iron addition modes (one: T1P, and two pulses: T2P) to imitate the iron increase produced by the downward migration of Microcystis spp. colonies. Our results show that iron is a growth-promoting factor and that its optimal range of concentrations for the growth of Microcystis spp. under the experimental setting conditions is between 700 and 1100 µg Fe·L⁻¹. On the other hand, growth rates were not significantly different between T1P and T2P; thus, different addition modes did not have an effect on growth. Regarding microcystin content, the MC quota in natural populations of Microcystis spp. did not show a clear relationship with the iron supply. This work contributes to the understanding of the underlying factors affecting cyanobacteria bloom formation and the production of MCs, which in turn would impact the development of management strategies to control cyanobacteria blooms. Full article

Microplastics are considered the most common waste in aquatic ecosystems, and studying them along with their interactions with biota are considered a priority. Here, results on the role of microplastics in the dispersion of microbes from terrestrial to aquatic ecosystems are presented. Data were obtained from microcosm experiments in which microplastics (plastic bags (BA), polyethylene bottles (BO), acrylic beads (BE), and cigarette butts (BU)) with their attached natural bacterial communities were inoculated in filtered and autoclaved lake water. The bacterial abundance on microplastics was estimated before inoculation using a protocol for the enumeration of sediment bacteria and ranged between 1.63 (BA) and 203.92 (BE) × 10³ cells mm⁻². Bacteria were released in the new medium, and their growth rates reached 5.8 d⁻¹. In the attached communities, Beta- (21.4%) and Alphaproteobacteria (18.6%) were the most abundant classes, while in the free-living communities Gammaproteobacteria dominated (48.07%). Abundant OTUs (≥1%) of the free-living communities were associated with the genera Acinetobacter, Pseudomonas, Ecidovorax, Delftia, Comamonas, Sphingopyxis, and Brevundimonas and members of the FCB group. Members of these genera are known to degrade natural or man-made organic compounds and have recently emerged as opportunistic pathogens. Thus, besides trophic transmission, microplastics can directly release bacteria in the environment, which could affect the health of humans, animals, and ecosystems. Full article

The phytoremediation potential of aquatic plants, particularly for Cu, is scarcely reported in the pertinent literature. In this regard, differential growth behavior and phytoaccumulation ability of three free-floating Azolla species (A. japonica, A. pinnata, and A. hybrid) were evaluated in a climatically controlled (a temperature of 25/20 °C, light/dark 16/8 h, a light intensity of 60 µmol m⁻² s⁻¹, and a relative humidity of 65%) microcosm study. Azolla plants were exposed to solutions having three Cu concentrations (0, 3, and 6 mg L⁻¹) under two incubation periods (4 and 8 days). Different Cu treatments significantly reduced Azolla biomass during both incubation periods and A. pinnata was the most sensitive species. Azolla plants grown in aqueous solutions showed substantial variations in Cu removal capacity. Higher bioconcentration values displayed by Azolla plants indicated that these plants can be deployed as potential plants for Cu removal from Cu contaminated water. Nevertheless, the plants exposed to higher Cu concentrations displayed color changes and root detachment due to Cu phytotoxic effects which may also ultimately lead to plant death. Significant correlations between Cu removed from the aqueous solutions and Cu contents of plant biomass indicated that Cu phytoremediation by Azolla plants was due to the phytoaccumulation mechanism because the removed Cu from aqueous solutions was accumulated in plant biomass. Introduced Azolla species, i.e., A. hybrid, displayed comparable Cu removal efficiency with naturally grown Azolla species, i.e., A. japonica and A. pinnata. Tested Azolla species proved to be suitable candidates to remediate Cu contaminated water and can be deployed for phytoremediation. Full article