Metatranscriptomic Insights Into the Response of River Biofilm Communities to Ionic and Nano-Zinc Oxide Exposures

Environmentally Relevant Antibiotic Concentrations Exert Stronger Selection Pressure on River Biofilm Resistomes than AMR-Reservoir Effluents

Freshwater environments are primary receiving systems of wastewater and effluents, which carry low concentrations of antibiotics and antimicrobial-resistant (AMR) bacteria and genes. Aquatic microbial communities are thus exposed to environmentally relevant concentrations of antibiotics (ERCA) that presumably influence the acquisition and spread of environmental AMR. Here, we analyzed ERCA exposure with and without the additional presence of municipal wastewater treatment plant effluent (W) and swine manure run-off (M) on aquatic biofilm resistomes. Microscopic analyses revealed decreased taxonomic diversity and biofilm structural integrity, while metagenomic analysis revealed an increased abundance of resistance, virulence, and mobile element-related genes at the highest ERCA exposure levels, with less notable impacts observed when solely exposed to W or M effluents. Microbial function predictions indicated increased gene abundance associated with energy and cell membrane metabolism and heavy metal resistance under ERCA conditions. In silico predictions of increased resistance mechanisms did not correlate with observed phenotypic resistance patterns when whole communities were exposed to antimicrobial susceptibility testing. This reveals important insight into the complexity of whole-community coordination of physical and genetic responses to selective pressures. Lastly, the environmental AMR risk assessment of metagenomic data revealed a higher risk score for biofilms grown at sub-MIC antibiotic conditions.

Sub-MIC antibiotics influence the microbiome, resistome and structure of riverine biofilm communities

The effects of sub-minimum inhibitory concentrations (sub-MICs) of antibiotics on aquatic environments is not yet fully understood. Here, we explore these effects by employing a replicated microcosm system fed with river water where biofilm communities were continuously exposed over an eight-week period to sub-MIC exposure (1/10, 1/50, and 1/100 MIC) to a mix of common antibiotics (ciprofloxacin, streptomycin, and oxytetracycline). Biofilms were examined using a structure-function approach entailing microscopy and metagenomic techniques, revealing details on the microbiome, resistome, virulome, and functional prediction. A comparison of three commonly used microbiome and resistome databases was also performed. Differences in biofilm architecture were observed between sub-MIC antibiotic treatments, with an overall reduction of extracellular polymeric substances and autotroph (algal and cyanobacteria) and protozoan biomass, particularly at the 1/10 sub-MIC condition. While metagenomic analyses demonstrated that microbial diversity was lowest at the sub-MIC 1/10 antibiotic treatment, resistome diversity was highest at sub-MIC 1/50. This study also notes the importance of benchmarking analysis tools and careful selection of reference databases, given the disparity in detected antimicrobial resistance genes (ARGs) identity and abundance across methods. Ultimately, the most detected ARGs in sub-MICs exposed biofilms were those that conferred resistance to aminoglycosides, tetracyclines, β-lactams, sulfonamides, and trimethoprim. Co-occurrence of microbiome and resistome features consistently showed a relationship between Proteobacteria genera and aminoglycoside ARGs. Our results support the hypothesis that constant exposure to sub-MICs antibiotics facilitate the transmission and promote prevalence of antibiotic resistance in riverine biofilms communities, and additionally shift overall microbial community metabolic function.

Soft X-ray Fluorescence and Near-Edge Absorption Microscopy for Investigating Metabolic Features in Biological Systems: A Review

Scanning transmission X-ray microscopy (STXM) provides the imaging of biological specimens allowing the parallel collection of localized spectroscopic information by X-ray fluorescence (XRF) and/or X-ray Absorption Near Edge Spectroscopy (XANES). The complex metabolic mechanisms which can take place in biological systems can be explored by these techniques by tracing even small quantities of the chemical elements involved in the metabolic pathways. Here, we present a review of the most recent publications in the synchrotrons' scenario where soft X-ray spectro-microscopy has been employed in life science as well as in environmental research.

Microbial indicators along a metallic contamination gradient in tropical coastal sediments

The structure and diversity of microbial community inhabiting coastal sediments reflect the exposition to contaminants. Aiming to assess the changes in the microbiota from Sepetiba Bay (SB, Brazil) sediments, correlations between the 16S rRNA gene data (V4-V5 region), metal contamination factors (CF), and the ecological risk classification provided by the Quality Ratio (QR) index were considered. The results show that microbial diversity differs significantly between the less (SB external sector) and the most (SB internal sector) polluted sectors. Also, differences in the microbial community structure regarding the ecological risk classifications validated the QR index as a reliable tool to report the SB chronic contamination. Microbial indicator genera resistant to metals (Desulfatiglans, SEEP-SRB1, Spirochaeta 2, among others) presented mainly anaerobic metabolisms. These genera are related to the sulfate reducing and methanogenic metabolisms probably participating in the natural attenuation processes but also associated with greenhouse gas emissions. In contrast, microbial indicator genera sensitive to metals (Rubripirellula, Blastopirellula, Aquibacter, among others) presented mainly aerobic metabolisms. It is suggested that future works should investigate the metabolic functions to evaluate the influence of metallic contaminants on microbial community inhabiting SB sediment.

Multi-omics eco-surveillance of bacterial community function in legacy contaminated estuary sediments

Complex legacy contamination is a major issue for many estuaries, with toxicity affecting change in bacterial communities, and their provision of associated goods and services. Sequencing surveys of bacterial community composition provide inferred function; however, additional insights may be generated by measurement of realised metabolic phenotypes. We apply multi-omics (genomics, lipidomics, and metabolomics), with traditional sediment quality analyses, to characterise sediment-associated bacterial communities in an estuary subject to legacy metal contamination (Zn, Hg, As, Cd, Cu and Pb). Analyses of bacterial composition and inferred function (genomics) are coupled with measurements of realised bacterial phenotype (metabolomics and lipidomics) at multiple industrialised and reference sites. At sites with the highest sediment metal concentrations (NTB), we also observed increased abundances of hydrocarbon and sulphuric acid metabolites, indicating additional sediment contamination. Bacterial phyla across sampled sites were dominated by Proteobacteria and Desulfobacteria. NTB sites were enriched with metabolically versatile, cooperative and biofilm forming phyla including, Zixibacteria, Spirochaetota, SAR324 clade, Proteobacteria, Latescibacterota, Desulfobacterota, Deferrisomtota and Acidobateriota; with inferred functions characterised by sulphur metabolism, pathways associated with the degradation of complex organic molecules, and fermentation. Reference sites were characterised by enhanced vitamin biosynthesis, cell wall, cofactor and carbohydrate biosynthesis, and CO₂ fixation. Measured metabolic phenotypes at NTB sites supported predicted functions, with most consistent change observed to naphthalene and aminobenzoate degradation pathways and carbohydrate metabolism (galactose, amino and nucleotide sugar). Change in NTB metabolite profiles was most highly correlated with sediment Hg concentrations, indicative of toxic exposure and potential for Hg methylation. Lipid profiles generated further insight into potential functional (hydroxy fatty acids) and community level change (ceramide phosphoethanolamines, unsaturated glycerides). Multi-omics outputs provided insights into bacterial community functions, modes of contaminant toxicity and expressed mechanisms of adaptation, necessary to better inform management decisions and predictive models in increasingly human-influenced environments.

How Do the Players Play? A Post-Genomic Analysis Paradigm to Understand Aquatic Ecosystem Processes

Culture-independent and meta-omics sequencing methods have shed considerable light on the so-called “microbial dark matter” of Earth’s environmental microbiome, improving our understanding of phylogeny, the tree of life, and the vast functional diversity of microorganisms. This influx of sequence data has led to refined and reimagined hypotheses about the role and importance of microbial biomass, that paradoxically, sequencing approaches alone are unable to effectively test. Post-genomic approaches such as metabolomics are providing more sensitive and insightful data to unravel the fundamental operations and intricacies of microbial communities within aquatic systems. We assert that the implementation of integrated post-genomic approaches, specifically metabolomics and metatranscriptomics, is the new frontier of environmental microbiology and ecology, expanding conventional assessments toward a holistic systems biology understanding. Progressing beyond siloed phylogenetic assessments and cataloging of metabolites, toward integrated analysis of expression (metatranscriptomics) and activity (metabolomics) is the most effective approach to provide true insight into microbial contributions toward local and global ecosystem functions. This data in turn creates opportunity for improved regulatory guidelines, biomarker discovery and better integration of modeling frameworks. To that end, critical aquatic environmental issues related to climate change, such as ocean warming and acidification, contamination mitigation, and macro-organism health have reasonable opportunity of being addressed through such an integrative approach. Lastly, we argue that the “post-genomics” paradigm is well served to proactively address the systemic technical issues experienced throughout the genomics revolution and focus on collaborative assessment of field-wide experimental standards of sampling, bioinformatics and statistical treatments.

Trace Metal Contamination Impacts Predicted Functions More Than Structure of Marine Prokaryotic Biofilm Communities in an Anthropized Coastal Area

Trace metal (TM) contamination in marine coastal areas is a worldwide threat for aquatic communities. However, little is known about the influence of a multi-chemical contamination on both marine biofilm communities' structure and functioning. To determine how TM contamination potentially impacted microbial biofilms' structure and their functions, polycarbonate (PC) plates were immerged in both surface and bottom of the seawater column, at five sites, along strong TM contamination gradients, in Toulon Bay. The PC plates were incubated during 4 weeks to enable colonization by biofilm-forming microorganisms on artificial surfaces. Biofilms from the PC plates, as well as surrounding seawaters, were collected and analyzed by 16S rRNA amplicon gene sequencing to describe prokaryotic community diversity, structure and functions, and to determine the relationships between bacterioplankton and biofilm communities. Our results showed that prokaryotic biofilm structure was not significantly affected by the measured environmental variables, while the functional profiles of biofilms were significantly impacted by Cu, Mn, Zn, and salinity. Biofilms from the contaminated sites were dominated by tolerant taxa to contaminants and specialized hydrocarbon-degrading microorganisms. Functions related to major xenobiotics biodegradation and metabolism, such as methane metabolism, degradation of aromatic compounds, and benzoate degradation, as well as functions involved in quorum sensing signaling, extracellular polymeric substances (EPS) matrix, and biofilm formation were significantly over-represented in the contaminated site relative to the uncontaminated one. Taken together, our results suggest that biofilms may be able to survive to strong multi-chemical contamination because of the presence of tolerant taxa in biofilms, as well as the functional responses of biofilm communities. Moreover, biofilm communities exhibited significant variations of structure and functional profiles along the seawater column, potentially explained by the contribution of taxa from surrounding sediments. Finally, we found that both structure and functions were significantly distinct between the biofilm and bacterioplankton, highlighting major differences between the both lifestyles, and the divergence of their responses facing to a multi-chemical contamination.