Periphytic Biofilm Formation on Natural and Artificial Substrates: Comparison of Microbial Compositions, Interactions, and Functions

Combined impacts of chlorine and pharmaceutical discharge on river periphyton and zoobenthos

Following the COVID-19 outbreak, a vast array of chlorine disinfectants was used to eliminate the virus, leading to inevitable discharge into aquatic ecosystems. These environments also contain various anthropogenic micropollutants, such as pharmaceuticals, which pose threats to the survival and activities of biological communities. Consequently, the presence of discharged chlorine disinfectants and pharmaceuticals can simultaneously impact the structure and function of aquatic ecosystems. To investigate the combined effects of chlorine disinfectants and pharmaceuticals on the periphyton and zoobenthos (Limnodrilus hoffmeisteri) community composition and function, we conducted a 12-flume reactor experiment using sodium hypochlorite and representative pharmaceuticals (abundant in the Yangtze River) as influents. Results demonstrated that the discharge of chlorine disinfectants further altered the composition of river prokaryotic communities. Eukaryotic organisms within the periphyton exhibited greater resilience to chlorine exposure compared to prokaryotic communities. Metagenomic analysis revealed that prokaryotic communities with different compositions can execute similar functions, while RNA sequencing indicated that co-exposure promoted biological processes such as focal adhesion and ribosome synthesis, but inhibited activities related to nitrogen metabolism and resistance to folate antimicrobials. Additionally, co-exposure induced oxidative stress in L. hoffmeisteri, leading to stronger environmental adaptation.

Temporal and Depth-Driven Variability of Pelagic Bacterial Communities in Lake Erie: Biofilm and Plankton Dynamics

Despite constituting an important component of freshwater ecosystems, biofilm assemblages have remained relatively understudied compared to plankton, especially in freshwater systems such as the western basin of Lake Erie (WBLE). This study therefore aimed to elucidate temporal and vertical shifts of microbial communities of planktonic and biofilm growth on artificial substrates in the WBLE water column at discrete depths, investigating the overlap of shared taxa between community types. Sequencing of the 16S rRNA gene revealed concurrent biofilm-plankton samples shared a low percentage (~10%) of amplicon sequence variants (ASVs) indicating distinct communities between free-living and substrate-attached bacteria. Plankton communities did not significantly differ between surface and bottom depths (1 and 8 m), whereas biofilm communities differed between upper (1-4 m) and lower (5-8 m) water columns. Temporal variation in community composition was observed in biofilm, with early periods (June-July) showing significant dissimilarity followed by compositional convergence in late summer onwards (August-October). With the expansion of artificial infrastructure in aquatic systems, there is novel substrate material to observe spatiotemporal patterns of microbial colonisation throughout the pelagic zone. These results demonstrate the complexity of bacterial biofilm communities from plankton in freshwater, providing insight into microbial assembly through temporal succession and across depth.

Migration of natural organic matter and Pseudomonas fluorescens-associated polystyrene on natural substrates in aquatic environments

This study investigated the migration behavior of microplastics (MPs) covered with natural organic matter (NOM) and biofilm on three substrates (silica, Pseudomonas fluorescent and Pseudomonas aeruginosa biofilms) in various ionic strengths, focusing on the alterations in surface properties based on surface energy theory that affected their deposition and release processes. Peptone and Pseudomonas fluorescens were employed to generate NOM-attached and biofilm-coated polystyrene (PS) (NOM-PS and Bio-PS). NOM-PS and Bio-PS both exhibited different surface properties, as increased roughness and particle sizes, more hydrophilic surfaces and altered zeta potentials which increased with ionic strength. Although the deposition of NOM-PS on biofilms were enhanced by higher ionic strengths and the addition of Ca2+, while Bio-PS deposited less on biofilms and more on the silica surface. Both types exhibited diffusion-driven adsorption on the silica surface, with Bio-PS also engaging in synergistic and competitive interactions on biofilm surfaces. Release tests revealed that NOM-PS and Bio-PS were prone to release from silica than from biofilms. The Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory furtherly demonstrated that mid-range electrostatic (EL) repulsion had significantly impacts on NOM-PS deposition, and structural properties of extracellular polymeric substances (EPS) and substrate could affect Bio-PS migration.

A comparison between constructed wetland substrates: Impacts on microbial community and wastewater treatment

Constructed wetlands (CWs) can play a crucial role in treating wastewater, and in the context of this study, the distillation byproduct of the whisky industry known as 'spent lees'. Here, we assess several different CW substrates (pea gravel, LECA and Alfagrog), with and without the addition of 20% biochar, in mesocosms set up to treat spent lees. Among the substrates tested, LECA + biochar and gravel + biochar showed promising results, with greater dissolved copper (dissCu) reduction, chemical oxygen demand (COD) removal, organic carbon (OC) reduction, and pH modulation. These findings indicate a potentially beneficial role for biochar in enhancing treatment efficacy, particularly in facilitating dissCu remediation and the removal of organic pollutants. In terms of microbial diversity, mesocosms including biochar generally had reduced bacterial alpha diversity, suggesting that 'fresh' (uncolonized) biochar may negatively affect microbial diversity in wetland ecosystems in the short term. After continuously supplying spent lees to mesocosms for 2-months, microbial diversity in each mesocosm dropped substantially, and moderate levels of bacterial community differentiation and high levels of fungal community differentiation were detected among mesocosms. The bacterial and fungal communities were also found to differ between the substrate and outlet water samples. Among the bacterial classes present in the mesocosms that may play a crucial role in water treatment performance, Gammaproteobacteria, Bacteroidia and Alphaproteobacteria should be further investigated. In terms of fungal classes, the role of Sordariomycetes should be explored in greater depth.

Seasonality of mercury and its fractions in microplastics biofilms -comparison to natural biofilms, suspended particulate matter and bottom sediment

Biofilms can enhance the sorption of heavy metals onto microplastic (MP) surfaces. However, most research in this field relies on laboratory experiments and neglects metal fractions and seasonal variations. Further studies of the metal/biofilm interaction in the aquatic environment are essential for assessing the ecological threat that MPs pose. The present study used in situ experiments in an environment conducive to biofouling (Vistula Lagoon, Baltic Sea). The objective was to investigate the sorption of mercury and its fractions (thermodesorption technique) in MP (polypropylene-PP, polystyrene-PS, polylactide-PLA) biofilms and natural matrices across three seasons. After one month of incubation, the Hg concentrations in MP and natural substratum (gravel grains-G) biofilms were similar (MP: 145 ± 45 ng/g d.w.; G: 132 ± 23 ng/g d.w.) and approximately twofold those of suspended particulate matter (SPM) (63 ± 27 ng/g d.w.). Hg concentrations in biofilms and sediments were similar, but labile fractions dominated in biofilms and stable fractions in sediments. Seasonal Hg concentrations in MP biofilms decreased over summer>winter>spring, with significant variation for mineral and loosely bound Hg fractions. Multiple regression analysis revealed that hydrochemical conditions and sediment resuspension played a crucial role in the observed variability. The influence of polymer type and morphology (pellets, fibres, aged MP) on Hg sorption in biofilms was visible only in high summer temperatures. In this season, PP fibres and aged PP pellets encouraged biofilm growth and the accumulation of labile Hg fractions. Additionally, high concentrations of mineral (stable and semi-labile) Hg fractions were found in expanded PS biofilms. These findings suggest that organisms that ingest MPs or feed on the biofilms are exposed to the adverse effects of Hg and the presence of MPs in aquatic ecosystems may facilitate the transfer of mercury within the food chain.

Plastic Litter Emits the Foraging Infochemical Dimethyl Sulfide after Submersion in Freshwater Rivers

Plastic pollution is widespread throughout aquatic environments globally, with many organisms known to interact with and ingest plastic. In marine environments, microbial biofilms that form on plastic surfaces can produce the odorous compound dimethyl sulfide (DMS), which is a known foraging cue. This has been shown to increase the ingestion of plastic by some invertebrates and therefore act as a biological factor which influences the risks of plastic to marine ecosystems. In freshwater however, the production of DMS has been largely overlooked, despite the known sensitivity of some freshwater species to this compound. To address this gap, the present study analyzed the production of DMS by biofilms which formed on low-density polyethylene and polylactic acid films after 3 and 6 weeks of submersion in either a rural or an urban United Kingdom river. Using gas chromatography-mass spectrometry, the production of DMS by these biofilms was consistently identified. The amount of DMS produced varied significantly across river locations and materials, with surfaces in the urban river generally producing a stronger signal and plastics producing up to seven times more DMS than glass control surfaces. Analysis of biofilm weight and photosynthetic pigment content indicated differences in biofilm composition across conditions and suggested that DMS production was largely driven by nonphotosynthetic taxa. For the first time this work has documented the production of DMS by plastic litter after submersion in freshwater rivers. Further work is now needed to determine if, as seen in marine systems, this production of DMS can encourage the interaction of freshwater organisms with plastic litter and therefore operate as a biological risk factor in the impacts of plastic on freshwater environments. Environ Toxicol Chem 2024;43:1485-1496. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

The Role of Metallurgical Features in the Microbially Influenced Corrosion of Carbon Steel: A Critical Review

Microbially influenced corrosion (MIC) is a potentially critical degradation mechanism for a wide range of materials exposed to environments that contain relevant microorganisms. The likelihood and rate of MIC are affected by microbiological, chemical, and metallurgical factors; hence, the understanding of the mechanisms involved, verification of the presence of MIC, and the development of mitigation methods require a multidisciplinary approach. Much of the recent focus in MIC research has been on the microbiological and chemical aspects, with less attention given to metallurgical attributes. Here, we address this knowledge gap by providing a critical synthesis of the literature on the metallurgical aspects of MIC of carbon steel, a material frequently associated with MIC failures and widely used in construction and infrastructure globally. The article begins by introducing the process of MIC, then progresses to explore the complexities of various metallurgical factors relevant to MIC in carbon steel. These factors include chemical composition, grain size, grain boundaries, microstructural phases, inclusions, and welds, highlighting their potential influence on MIC processes. This review systematically presents key discoveries, trends, and the limitations of prior research, offering some novel insights into the impact of metallurgical factors on MIC, particularly for the benefit of those already familiar with other aspects of MIC. The article concludes with recommendations for documenting metallurgical data in MIC research. An appreciation of relevant metallurgical attributes is essential for a critical assessment of a material's vulnerability to MIC to advance research practices and to broaden the collective knowledge in this rapidly evolving area of study.

Aquatic plastisphere: Interactions between plastics and biofilms

Because of the high production rates, low recycling rates, and poor waste management of plastics, an increasing amount of plastic is entering the aquatic environment, where it can provide new ecological niches for microbial communities and form a so-called plastisphere. Recent studies have focused on the one-way impact of plastic substrata or biofilm communities. However, our understanding of the two-way interactions between plastics and biofilms is still limited. This review first summarizes the formation process and the co-occurrence network analysis of the aquatic plastisphere to comprehensively illustrate the succession pattern of biofilm communities and the potential consistency between keystone taxa and specific environmental behavior of the plastisphere. Furthermore, this review sheds light on mutual interactions between plastics and biofilms. Plastic properties, environmental conditions, and colonization time affect biofilm development. Meanwhile, the biofilm communities, in turn, influence the environmental behaviors of plastics, including transport, contaminant accumulation, and especially the fragmentation and degradation of plastics. Based on a systematic literature review and cross-referencing from these disciplines, the current research focus, and future challenges in exploring aquatic plastisphere development and biofilm-plastic interactions are proposed.

Artificial substrata to assess ecological and ecotoxicological responses in river biofilms: Use and recommendations

River biofilms are biological consortia of autotrophs and heterotrophs colonizing most solid surfaces in rivers. Biofilm composition and biomass differ according to the environmental conditions, having different characteristics between systems and even between river habitats. Artificial substrata (AS) are an alternative for in situ or laboratory experiments to handle the natural variability of biofilms. However, specific research goals may require decisions on colonization time or type of substrata. Substrata properties (i.e., texture, roughness, hydrophobicity) and the colonization period and site are selective factors of biofilm characteristics. Here we describe the uses of artificial substrata in the assessment of ecological and ecotoxicological responses and propose a decision tree for the best use of artificial substrata in river biofilm studies. We propose departing from the purpose of the study to define the necessity of obtaining a realistic biofilm community, from which it may be defined the colonization time, the colonization site, and the type of artificial substratum. Having a simple or mature biofilm community should guide our decisions on the colonization time and type of substrata to be selected for the best use of AS in biofilm studies. Tests involving contaminants should avoid adsorbing materials while those ecologically oriented may use any AS mimicking those substrata occurring in the streambed.•We review the utilization of different artificial substrata to colonize biofilm in river ecology and ecotoxicology.•We propose a decision tree to guide on selecting the appropriate artificial substrata and colonization site and duration.•Type of artificial substrata (material, size, shape...) and colonization duration are to be decided according to the specific purpose of the study.

Molecular regulation of conditioning film formation and quorum quenching in sulfate reducing bacteria

Sensing surface topography, an upsurge of signaling biomolecules, and upholding cellular homeostasis are the rate-limiting spatio-temporal events in microbial attachment and biofilm formation. Initially, a set of highly specialized proteins, viz. conditioning protein, directs the irreversible attachment of the microbes. Later signaling molecules, viz. autoinducer, take over the cellular communication phenomenon, resulting in a mature microbial biofilm. The mandatory release of conditioning proteins and autoinducers corroborated the existence of two independent mechanisms operating sequentially for biofilm development. However, both these mechanisms are significantly affected by the availability of the cofactor, e.g., Copper (Cu). Generally, the Cu concentration beyond threshold levels is detrimental to the anaerobes except for a few species of sulfate-reducing bacteria (SRB). Remarkably SRB has developed intricate ways to resist and thrive in the presence of Cu by activating numerous genes responsible for modifying the presence of more toxic Cu(I) to Cu(II) within the periplasm, followed by their export through the outer membrane. Therefore, the determinants of Cu toxicity, sequestration, and transportation are reconnoitered for their contribution towards microbial adaptations and biofilm formation. The mechanistic details revealing Cu as a quorum quencher (QQ) are provided in addition to the three pathways involved in the dissolution of cellular communications. This review articulates the Machine Learning based data curing and data processing for designing novel anti-biofilm peptides and for an in-depth understanding of QQ mechanisms. A pioneering data set has been mined and presented on the functional properties of the QQ homolog in Oleidesulfovibrio alaskensis G20 and residues regulating the multicopper oxidase properties in SRB.

Bacterial colonisation of plastic in the Rockall Trough, North-East Atlantic: An improved understanding of the deep-sea plastisphere

Plastic pollution has now been found within multiple ecosystems across the globe. Characterisation of microbial assemblages associated with marine plastic, or the so-called 'plastisphere', has focused predominantly on plastic in the epipelagic zone. Whether this community includes taxa that are consistently enriched on plastic compared to surrounding non plastic surfaces is unresolved, as are the ecological implications. The deep sea is likely a final sink for most of the plastic entering the ocean, yet there is limited information on microbial colonisation of plastic at depth. The aim of this study was to investigate deep-sea microbial communities associated with polystyrene (PS) and polyurethane (PU) with Bath stone used as a control. The substrates (n = 15) were deployed in the Rockall Trough (Atlantic), and recovered 420 days later from a depth of 1796 m. To characterise the bacterial communities, 16S rRNA genes were sequenced using the Illumina MiSeq platform. A dominant core microbiome (taxa shared across all substrates) comprised 8% of total ASVs (amplicon sequence variant) and accounted for 92% of the total community reads. This suggests that many commonly reported members of the plastisphere are simply opportunistic which freely colonise any hard surface. Transiently associated species consisted of approximately 7% of the total community. Thirty genera were enriched on plastic (P < 0.05), representing 1% of the total community. The discovery of novel deep-sea enriched taxa included Aurantivirga, Algivirga, IheB3-7, Spirosoma, HTCC5015, Ekhidna and Calorithrix on PS and Candidatus Obscuribacter, Haloferula, Marine Methylotrophic Group 3, Aliivibrio, Tibeticola and Dethiosulfatarculus on PU. This small fraction of the microbiome include taxa with unique metabolic abilities and show how bacterial communities can be shaped by plastic pollution at depth. This study outlines a novel approach in categorising the plastisphere to elucidate the ecological implications of enriched taxa that show an affinity for colonising plastic.

Soil plastisphere: Exploration methods, influencing factors, and ecological insights

Microplastic (MP), an emerging contaminant, is globally prevalent and poses potential environmental threats and ecological risks to both aquatic and terrestrial ecosystems. When MPs enter into natural environments, they may serve as artificial substrates for microbial colonization and plastisphere formation, providing new ecological niches for microorganisms. Recent studies of the plastisphere have focused on aquatic ecosystems. However, our understanding of the soil plastisphere e.g. its formation process, microbial ecology, co-transport of organic pollutants and heavy metals, and effects on biogeochemical processes is still very limited. This review summarizes latest methods used to explore the soil plastisphere, assesses the factors influencing the microbial ecology of the soil plastisphere, and sheds light on potential ecological risks caused by the soil plastisphere. The formation and succession of soil plastisphere communities can be driven by MP characteristics and soil environmental factors. The soil plastisphere may affect a series of ecological processes, especially the co-transport of environmental contaminants, biodegradation of MPs, and soil carbon cycling. We aim to narrow the knowledge gap between the soil and aquatic plastisphere, and provide valuable guidance for future research on the soil plastisphere in MP-contaminated soils.

Formation, Development, and Cross-Species Interactions in Biofilms

Biofilms, which are essential vectors of bacterial survival, protect microbes from antibiotics and host immune attack and are one of the leading causes that maintain drug-resistant chronic infections. In nature, compared with monomicrobial biofilms, polymicrobial biofilms composed of multispecies bacteria predominate, which means that it is significant to explore the interactions between microorganisms from different kingdoms, species, and strains. Cross-microbial interactions exist during biofilm development, either synergistically or antagonistically. Although research into cross-species biofilms remains at an early stage, in this review, the important mechanisms that are involved in biofilm formation are delineated. Then, recent studies that investigated cross-species cooperation or synergy, competition or antagonism in biofilms, and various components that mediate those interactions will be elaborated. To determine approaches that minimize the harmful effects of biofilms, it is important to understand the interactions between microbial species. The knowledge gained from these investigations has the potential to guide studies into microbial sociality in natural settings and to help in the design of new medicines and therapies to treat bacterial infections.