Pollution impacts on bacterioplankton diversity in a tropical urban coastal lagoon system

Biodegradation of microplastic in freshwaters: A long-lasting process affected by the lake microbiome

Plastics have been produced for over a century, but definitive evidence of complete plastic biodegradation in different habitats, particularly freshwater ecosystems, is still missing. Using 13 C-labelled polyethylene microplastics (PE-MP) and stable isotope analysis of produced gas and microbial membrane lipids, we determined the biodegradation rate and fate of carbon in PE-MP in different freshwater types. The biodegradation rate in the humic-lake waters was much higher (0.45% ± 0.21% per year) than in the clear-lake waters (0.07% ± 0.06% per year) or the artificial freshwater medium (0.02% ± 0.02% per year). Complete biodegradation of PE-MP was calculated to last 100-200 years in humic-lake waters, 300-4000 years in clear-lake waters, and 2000-20,000 years in the artificial freshwater medium. The concentration of 18:1ω7, characteristic phospholipid fatty acid in Alpha- and Gammaproteobacteria, was a predictor of faster biodegradation of PE. Uncultured Acetobacteraceae and Comamonadaceae among Alpha- and Gammaproteobacteria, respectively, were major bacteria related to the biodegradation of PE-MP. Overall, it appears that microorganisms in humic lakes with naturally occurring refractory polymers are more adept at decomposing PE than those in other waters.

Aliphatic and polycyclic aromatic hydrocarbons in surface sediments as a tool for the assessment of the contamination status of mangrove forests in Rio de Janeiro (Brazil)

The distribution of aliphatic and polycyclic aromatic hydrocarbons (PAHs) in surface sediments from mangrove forests of the Rio de Janeiro State was investigated. Ten sampling stations were selected in the mangroves of Sepetiba Bay and the Jacarepaguá Lagoon Complex (JLC), which are areas affected by multiple human activities. The total aliphatic hydrocarbons concentrations showed marked variation between samples (27-407 μg g^-1), mostly related to the total organic carbon contents. The total PAHs concentration ranged between 38 and 792 ng g^-1. Diagnostic indices and statistical analysis showed that the mangrove forests can be divided into three groups: the western portion of Sepetiba Bay with the lowest level of contamination; the inner portion of the bay with the most intense presence of local sources of contamination, especially of pyrolytic character; and the JLC with a greater accumulation of hydrocarbons, mainly derived from petroleum combustion, resultant from the intense urbanization.

Ecological risk assessment of metal and hydrocarbon pollution in sediments from an urban tropical estuary: Tijuca lagoon (Rio de Janeiro, Brazil)

Urban tropical lagoons are often impacted by eutrophication, metal, and polycyclic aromatic hydrocarbon (PAH) contamination, but the toxicity of their bottom sediments is still poorly investigated in South America. Aiming to contribute to filling this gap, a sediment quality assessment was conducted in the Tijuca Lagoon (Rio de Janeiro, Brazil) using different lines of evidence (LOEs) including sediment characterization, determination of metals and PAHs, and acute toxicity testing with burrowing amphipods (Tiburonella viscana). Mud and organic matter contents played a crucial role in contaminant distribution along the lagoon. The concentrations of PAH were generally low (mean ΣPAH = 795.42 ± 1146.2 ng/g; n = 23), but a contamination hotspot of light PAH compounds was identified. Such PAHs were mainly pyrolytic, probably related to the deposition of atmospheric pollution, although petrogenic compounds also occur in the lagoon. The data indicated the occurrence of geochemical anomalies of Zn, Cu, Pb, and Hg (mean values = 176.9 ± 91.6, 45.1 ± 21.3, 35.2 ± 15.0, 0.1442 ± 0.0893 mg/kg, respectively; n = 23), probably associated with industrial wastes, garbage deposition, urban runoff, and domestic sewage contributions. The mortality of T. viscana was significant for more than 85% of the samples (mean mortality = 70.3 ± 26.0%; n = 23), but it was not significantly correlated with PAH and metal concentrations. On the other side, domestic sewage contributions and eutrophication seem to play a relevant role in sediment toxicity. Actually, the toxicity observed in the tests seems to be due to the simultaneous influence of multiple toxicants and their combined effects on the organisms. Such stressors may include not only metals, PAH, and eutrophication but also chemicals not evaluated in this study, such as hormones, pharmaceuticals and personal care compounds, perfluorocompounds, detergents, and others.

Microcystin drives the composition of small-sized bacterioplankton communities from a coastal lagoon

Cyanobacterial blooms affect biotic interactions in aquatic ecosystems, including those involving heterotrophic bacteria. Ultra-small microbial communities are found in both surface water and groundwater and include diverse heterotrophic bacteria. Although the taxonomic composition of these communities has been described in some environments, the involvement of these small cells in the fate of environmentally relevant molecules has not been investigated. Here, we aimed to test if small-sized microbial fractions from a polluted urban lagoon were able to degrade the cyanotoxin microcystin (MC). We obtained cells after filtration through 0.45 as well as 0.22 μm membranes and characterized the morphology and taxonomic composition of bacteria before and after incubation with and without microcystin-LR (MC-LR). Communities from different size fractions (< 0.22 and < 0.45 μm) were able to remove the dissolved MC-LR. The originally small-sized cells grew during incubation, as shown by transmission electron microscopy, and changed in both cell size and morphology. The analysis of 16S rDNA sequences revealed that communities originated from < 0.22 and < 0.45 μm fractions diverged in taxonomic composition although they shared certain bacterial taxa. The presence of MC-LR shifted the structure of < 0.45 μm communities in comparison to those maintained without toxin. Actinobacteria was initially dominant and after incubation with MC-LR Proteobacteria predominated. There was a clear enhancement of taxa already known to degrade MC-LR such as Methylophilaceae. Small-sized bacteria constitute a diverse and underestimated fraction of microbial communities, which participate in the dynamics of MC-LR in natural environments.

Greenhouse gas emissions (CO2 and CH4) and inorganic carbon behavior in an urban highly polluted tropical coastal lagoon (SE, Brazil)

Increasing eutrophication of coastal waters generates disturbances in greenhouse gas (GHG) concentrations and emissions to the atmosphere that are still poorly documented, particularly in the tropics. Here, we investigated the concentrations and diffusive fluxes of carbon dioxide (CO₂) and methane (CH₄) in the urban-dominated Jacarepagua Lagoon Complex (JLC) in Southeastern Brazil. This lagoonal complex receives highly polluted freshwater and shows frequent occurrences of anoxia and hypoxia and dense phytoplankton blooms. Between 2017 and 2018, four spatial surveys were performed (dry and wet conditions), with sampling in the river waters that drain the urban watershed and in the lagoon waters with increasing salinities. Strong oxygen depletion was found in the rivers, associated with extremely high values of partial pressure of CO₂ (pCO₂; up to 20,417 ppmv) and CH₄ concentrations (up to 288,572 nmol L^-1). These high GHG concentrations are attributed to organic matter degradation from untreated domestic effluents mediated by aerobic and anaerobic processes, with concomitant production of total alkalinity (TA) and dissolved inorganic carbon (DIC). In the lagoon, GHG concentrations decreased mainly due to dilution with seawater and degassing. In addition, the phytoplankton growth and CH₄ oxidation apparently consumed some CO₂ and CH₄, respectively. TA concentrations showed a marked minimum at salinity of ~20 compared to the two freshwater and marine end members, indicating processes of re-oxidation of inorganic reduced species from the low-salinity region, such as ammonia, iron, and/or sulfides. Diffusive emissions of gases from the entire lagoon ranged from 22 to 48 mmol C m^-2 d^-1 for CO₂ and from 2.2 to 16.5 mmol C m^-2 d^-1 for CH₄. This later value is among the highest documented in coastal waters. In terms of global warming potential (GWP) and CO₂ equivalent emissions (CO₂-eq), the diffusive emissions of CH₄ were higher than those of CO₂. These results highlight that highly polluted coastal ecosystems are hotspots of GHG emissions to the atmosphere, which may become increasingly significant in future global carbon budgets.

Modelling the influence of environmental parameters over marine planktonic microbial communities using artificial neural networks

Guanabara Bay is a tropical estuarine ecosystem that receives massive anthropogenic impacts from the metropolitan region of Rio de Janeiro. This ecosystem suffers from an ongoing eutrophication process that has been shown to promote the emergence of potentially pathogenic bacteria, giving rise to public health concerns. Although previous studies have investigated how environmental parameters influence the microbial community of Guanabara Bay, they often have been limited to small spatial and temporal gradients and have not been integrated into predictive mathematical models. Our objective was to fill this knowledge gap by building models that could predict how temperature, salinity, phosphorus, nitrogen and transparency work together to regulate the abundance of bacteria, chlorophyll and Vibrio (a potential human pathogen) in Guanabara Bay. To that end, we built artificial neural networks to model the associations between these variables. These networks were carefully validated to ensure that they could provide accurate predictions without biases or overfitting. The estimated models displayed high predictive capacity (Pearson correlation coefficients ≥0.67 and root mean square error ≤ 0.55). Our findings showed that temperature and salinity were often the most important factors regulating the abundance of bacteria, chlorophyll and Vibrio (absolute importance ≥5) and that each of these has a unique level of dependence on nitrogen and phosphorus for their growth. These models allowed us to estimate the Guanabara Bay microbiome's response to changes in environmental conditions, which allowed us to propose strategies for the management and remediation of Guanabara Bay.

Genomic basis of antibiotic resistance in Vibrio parahaemolyticus strain JPA1

A multi-resistant strain of Vibrio parahaemolyticus was isolated from a tropical estuary in Rio de Janeiro, Brazil. Genome sequencing was conducted to establish the molecular basis of antibiotic resistance in this organism. The genetic content of this strain revealed it to be a non-virulent lineage that nevertheless possesses several antibiotic resistance determinants.

Do pharmaceuticals reach and affect the aquatic ecosystems in Brazil? A critical review of current studies in a developing country

Pharmaceutical residues are not completely removed in wastewater treatment plants (WWTPs) becoming contaminants in aquatic ecosystems. Thereby, it is important to investigate their concentrations in the environment and the possible consequences of their occurrence, including for human health. Here, we briefly reviewed the paths of pharmaceuticals to reach the environment, their behavior and fate in the environment, and the possible consequences of their occurrence. Moreover, we synthetized all the studies about the detection of pharmaceuticals in Brazilian water bodies and the available ecotoxicological knowledge on their effects. In this study, when we compare the data found on these compounds worldwide, we observed that Brazilian surface waters present considerable concentrations of 17α-ethinylestradiol, 17β-estradiol, and caffeine. In general, concentrations found in aquatic systems worldwide seems to be low; however, ecotoxicological tests showed that even these low concentrations can cause sublethal effects in biota. The knowledge about the effects of continuous exposure and mixtures is sparse. In summary, new research is urgently required about the effects of these compounds in biota-including long-term exposition and mixture tests-and on specific technologies to remove these compounds in water bodies and WWTPs, besides the introduction of new policies for pharmaceutical use.

Antibiotic resistance is widespread in urban aquatic environments of Rio de Janeiro, Brazil

Bacterial resistance to antibiotics has become a public health issue. Over the years, pathogenic organisms with resistance traits have been studied due to the threat they pose to human well-being. However, several studies raised awareness to the often disregarded importance of environmental bacteria as sources of resistance mechanisms. In this work, we analyze the diversity of antibiotic-resistant bacteria occurring in aquatic environments of the state of Rio de Janeiro, Brazil, that are subjected to distinct degrees of anthropogenic impacts. We access the diversity of aquatic bacteria capable of growing in increasing ampicillin concentrations through 16S rRNA gene libraries. This analysis is complemented by the characterization of antibiotic resistance profiles of isolates obtained from urban aquatic environments. We detect communities capable of tolerating antibiotic concentrations up to 600 times higher than the clinical levels. Among the resistant organisms are included potentially pathogenic species, some of them classified as multiresistant. Our results extend the knowledge of the diversity of antibiotic resistance among environmental microorganisms and provide evidence that the diversity of drug-resistant bacteria in aquatic habitats can be influenced by pollution.