Influence of surface characteristics on biofouling formed on polymers exposed to coastal sea waters of India

Responses of nitrobenzene removal performance and microbial community by modified biochar supported zerovalent iron in anaerobic soil

Biochar-supported ZVI have received increasing attention for their potential to remove nitrobenzene in groundwater and soil. However, the capacity of this material to enhance the biological reduction of nitrobenzene and alter microbial communities in anaerobic groundwater have not been explored. In this study, the nitrobenzene removal performance and mechanism of modified biochar-supported zerovalent iron (ZVI) composites were explored in anaerobic soil. The results showed that the 700 °C biochar composite enhanced the removal of nitrobenzene and inhibited its release from soil to the aqueous phase. NaOH-700-Fe50 had the highest removal rate of nitrobenzene, reaching 64.4%. However, the 300 °C biochar composite inhibited the removal of nitrobenzene. Microbial degradation rather than ZVI-mediated reduction was the main nitrobenzene removal pathway. The biochar composites changed the richness and diversity of microbial communities. ZVI enhanced the symbiotic relationship between microbial genera and weakened competition between soil microbial genera. In summary, the 700 °C modified biochar composite enhanced the removal of nitrobenzene by increasing microbial community richness and diversity, by upregulating functional genes, and by promoting electron transfer. Overall, the modified biochar-supported ZVI composites could be used for soil remediation, and NaOH-700-Fe50 is a promising composite material for the on-site remediation of nitrobenzene-contaminated groundwater.

Surface-associated bacterial assemblages on marine anthropogenic litter in the intertidal zone of the Arabian Sea, India

Anthropogenic marine litter (mainly plastic pollution) is a serious concern globally. The interactions between terrestrial and marine ecosystems lead to the accumulation of marine litter in the intertidal zone. The biofilm-forming bacteria tend to colonize on surfaces of marine litter which are composed of diverse bacteria and are less studied. The present study investigated the bacterial community composition using both culturable and non-culturable (Next-generation sequencing (NGS)) approaches associated with the marine litter (polyethylene (PE), styrofoam (SF) and fabric (FB)) at three distinct locations (Alang, Diu and Sikka) of the Arabian Sea, Gujarat, India. Predominant bacteria observed using culturable and NGS techniques belonged to Proteobacteria phyla. Alphaproteobacteria class dominated on polyethylene and styrofoam surfaces in the culturable fraction among the sites while the Bacillus dominated fabric surfaces. In the metagenomics fraction, Gammaproteobacteria dominated the surfaces except for PE and SF surfaces from Sikka and Diu, respectively. The PE surface at Sikka was dominated by Fusobacteriia while SF surface from Diu was dominated by Alphaproteobacteria. Both culture-dependent and NGS approaches identified hydrocarbon-degrading bacteria as well as pathogenic bacteria on the surfaces. The outcome of the present study illustrates diverse bacterial assemblages which occur on marine litter and increases our understanding of the plastisphere community.

Micron-Scale Biogeography of Seawater Biofilm Colonies at Submersed Solid Substrata Affected by Organic Matter and Microbiome Transformation in the Baltic Sea

The aim of this research was to determine temporal and spatial evolution of biofilm architecture formed at model solid substrata submersed in Baltic sea coastal waters in relation to organic matter transformation along a one-year period. Several materials (metals, glass, plastics) were deployed for a certain time, and the collected biofilm-covered samples were studied with a confocal microscopy technique using the advanced programs of image analysis. The geometric and structural biofilm characteristics: biovolume, coverage fraction, mean thickness, spatial heterogeneity, roughness, aggregation coefficient, etc., turned out to evolve in relation to organic matter transformation trends, trophic water status, microbiome evolution, and biofilm micro-colony transition from the heterotrophic community (mostly bacteria) to autotrophic (diatom-dominated) systems. The biofilm morphology parameters allowed the substratum roughness, surface wettability, chromatic organisms colony adaptation to substrata, and quorum sensing or cell to cell signaling effects to be quantitatively evaluated. In addition to the previous work, the structural biofilm parameters could become further novel trophic state indicators.

Bacterial community structure of early-stage biofilms is dictated by temporal succession rather than substrate types in the southern coastal seawater of India

Bacterial communities colonized on submerged substrata are recognized as a key factor in the formation of complex biofouling phenomenon in the marine environment. Despite massive maritime activities and a large industrial sector in the nearshore of the Laccadive Sea, studies describing pioneer bacterial colonizers and community succession during the early-stage biofilm are scarce. We investigated the biofilm-forming bacterial community succession on three substrata viz. stainless steel, high-density polyethylene, and titanium over 15 days of immersion in the seawater intake area of a power plant, located in the southern coastal region of India. The bacterial community composition of biofilms and peripheral seawater were analyzed by Illumina MiSeq sequenced 16S rRNA gene amplicons. The obtained metataxonomic results indicated a profound influence of temporal succession over substrate type on the early-stage biofilm-forming microbiota. Bacterial communities showed vivid temporal dynamics that involved variations in abundant bacterial groups. The proportion of dominant phyla viz. Proteobacteria decreased over biofilm succession days, while Bacteroidetes increased, suggesting their role as initial and late colonizers, respectively. A rapid fluctuation in the proportion of two bacterial orders viz. Alteromonadales and Vibrionales were observed throughout the successional stages. LEfSe analysis identified specific bacterial groups at all stages of biofilm development, whereas no substrata type-specific groups were observed. Furthermore, the results of PCoA and UPGMA hierarchical clustering demonstrated that the biofilm-forming community varied considerably from the planktonic community. Phylum Proteobacteria preponderated the biofilm-forming community, while the Bacteroidetes, Cyanobacteria, and Actinobacteria dominated the planktonic community. Overall, our results refute the common assumption that substrate material has a decisive impact on biofilm formation; rather, it portrayed that the temporal succession overshadowed the influence of the substrate material. Our findings provide a scientific understanding of the factors shaping initial biofilm development in the marine environment and will help in designing efficient site-specific anti-biofouling strategies.

Effect of polymeric support material on biofilm development, bacterial population, and wastewater treatment performance in anaerobic fixed-film systems

This study evaluated the performance of high-density polyethylene (HDPE), acrylonitrile butadiene styrene (ABS), polycarbonate (PC), polyvinylchloride (PVC), polypropylene (PP), polyvinylidene fluoride (PVDF) and polymethyl methacrylate (acrylic) when used as a support media in anaerobic attached-growth wastewater treatment systems. A combination of physical and chemical (total solids, protein, phosphorus, ammonia, chemical oxygen demand) methods, environmental scanning electron microscopy (ESEM) and Live/Dead viability assay) and genetic sequencing over a period of 81 days was used to provide an in-depth understanding of the impact of different polymer materials on biofilm formation, bacteria population, and wastewater treatment performance. The results showed that hydrophobic polymeric materials (i.e., PP and PVDF) promoted initial cell adhesion and biofilm formation (<16 days) better than the hydrophilic (i.e., ABS and HDPE) polymeric materials. However, under longer-term and steady-state operation (after 81 days), the hydrophilic materials demonstrated larger mature biofilm quantities and better wastewater treatment performance. The sequencing data showed biofilm bacterial community structures of the ABS and HDPE to be significantly different compared to the other polymeric materials tested. The data showed a positive correlation as well between the phyla present on the ABS and HDPE and COD removal. These results suggest that the type of polymeric material play an important role in biofilm development, bacterial population diversity, and wastewater treatment performance for anaerobic fixed-film systems, and ABS and HDPE performed better than the widely used PVC in the industry.

Ranking environmental degradation trends of plastic marine debris based on physical properties and molecular structure

As plastic marine debris continues to accumulate in the oceans, many important questions surround this global dilemma. In particular, how many descriptors would be necessary to model the degradation behavior of ocean plastics or understand if degradation is possible? Here, we report a data-driven approach to elucidate degradation trends of plastic debris by linking abiotic and biotic degradation behavior in seawater with physical properties and molecular structures. The results reveal a hierarchy of predictors to quantify surface erosion as well as combinations of features, like glass transition temperature and hydrophobicity, to classify ocean plastics into fast, medium, and slow degradation categories. Furthermore, to account for weathering and environmental factors, two equations model the influence of seawater temperature and mechanical forces.

Accumulation of micro and nano-plastic in the oceans has emerged as a global challenge. Here, the authors predict a hierarchy of features that regulate their degradation and surface erosion by a thorough analysis of polymer structure, composition, physical properties and degradation data.

Substantially enhanced anaerobic reduction of nitrobenzene by biochar stabilized sulfide-modified nanoscale zero-valent iron: Process and mechanisms

Nanoscale zero-valent iron (nZVI), although being increasingly used in anaerobic systems for strengthening the removal of various refractory pollutants, is limited by various inherent drawbacks, such as easy precipitation, passivation, poor mass and electron transfer. To address the above issues, biochar stabilized sulfide-modified nZVI (S-nZVI@BC) was added into an up-flow anaerobic sludge blanket (UASB) to investigate the enhancement of anaerobic biodegradation of nitrobenzene (NB) and its impacts on microbial community structure. The results demonstrated that both NB reduction and aniline formation could be substantially facilitated in S-nZVI@BC coupled system compared to other anaerobic ones coupled with nZVI or S-nZVI. The dosage of S-nZVI@BC resulted in the formation of densely packed aggregates, evidently increased the extracellular polymeric substances content, promoted the volatile fatty acids transformation and stimulated the methane yield. Furthermore, species related to fermentation (Bacteroides and Longilinea), methanogenesis (Methanosarcina and Methanomethylovorans), electroactivity (Pelobacter, Thiobacillus and Phaselicystis) as well as reduction (Desulfovibrio) were considerably enriched in S-nZVI@BC coupled system. The activities of electron transport, total adenosine triphosphate, nitroreductase and NAD(P)H, which were closely related to microbial activity and NB transformation, were increased noticeably in S-nZVI@BC coupled anaerobic system. This study demonstrated the promising potential for long-term operation and full-scale application of S-nZVI@BC coupled system for the treatment of NB containing wastewater.

Microbial Diversity and Putative Opportunistic Pathogens in Dishwasher Biofilm Communities

Extreme habitats are not only limited to natural environments, but also exist in manmade systems, for instance, household appliances such as dishwashers. Limiting factors, such as high temperatures, high and low pHs, high NaCl concentrations, presence of detergents, and shear force from water during washing cycles, define microbial survival in this extreme system. Fungal and bacterial diversity in biofilms isolated from rubber seals of 24 different household dishwashers was investigated using next-generation sequencing. Bacterial genera such as Pseudomonas, Escherichia, and Acinetobacter, known to include opportunistic pathogens, were represented in most samples. The most frequently encountered fungal genera in these samples belonged to Candida, Cryptococcus, and Rhodotorula, also known to include opportunistic pathogenic representatives. This study showed how specific conditions of the dishwashers impact the abundance of microbial groups and investigated the interkingdom and intrakingdom interactions that shape these biofilms. The age, usage frequency, and hardness of incoming tap water of dishwashers had significant impact on bacterial and fungal community compositions. Representatives of Candida spp. were found at the highest prevalence (100%) in all dishwashers and are assumed to be one of the first colonizers in recently purchased dishwashers. Pairwise correlations in tested microbiomes showed that certain bacterial groups cooccur, as did the fungal groups. In mixed bacterial-fungal biofilms, early adhesion, contact, and interactions were vital in the process of biofilm formation, where mixed complexes of bacteria and fungi could provide a preliminary biogenic structure for the establishment of these biofilms.

IMPORTANCE Worldwide demand for household appliances, such as dishwashers and washing machines, is increasing, as is the number of immunocompromised individuals. The harsh conditions in household dishwashers should prevent the growth of most microorganisms. However, our research shows that persisting polyextremotolerant groups of microorganisms in household appliances are well established under these unfavorable conditions and supported by the biofilm mode of growth. The significance of our research is in identifying the microbial composition of biofilms formed on dishwasher rubber seals, how diverse abiotic conditions affect microbiota, and which key microbial members were represented in early colonization and contamination of dishwashers, as these appliances can present a source of domestic cross-contamination that leads to broader medical impacts.

Nutrient capture and recycling by periphyton attached to modified agrowaste carriers

The reuse of periphytic biofilm from traditional wastewater treatment (i.e., active sludge process) is inefficient to recycle nutrients due to low accumulation of nutrients. Then, in this study, peanut shell (PS), rice husk (RH), decomposed peanut shell (DPS), acidified rice husks (ARH), and a commonly used carrier-ceramsite (C, as the control)-were used to support the growth of periphyton. Results showed that DPS and ARH supported significantly higher periphyton biomass and metabolic versatility than PS and RH, respectively, due to the increased presence of positive groups. The total nitrogen (TN) and total phosphorus (TP) captured by periphyton were enhanced by 600-657 and 833-3255 % for DPS, and 461-1808 and 21-308 % for ARH, respectively. The removal of nutrients from simulated eutrophic surface waters using periphyton attached to DPS was improved by 24-47 % for TP, 12-048 % for TN, and 15-78 % for nitrate compared to the control. The results indicate that the periphyton attached to modified agrowaste was capable of efficiently entrapping and storing N and P from eutrophic water. This study also implies that the mixture of periphyton and the modified agrowaste carriers are promising raw materials of biofertilizer.

Comparison of the properties of periphyton attached to modified agro-waste carriers

Periphyton is a valuable, environmentally benign resource widely used in environmental remediation. A protocol for reusing agro-wastes to improve the metabolic activity and versatility of periphyton was tested in this study. Peanut shell (PS), decomposed peanut shell (DPS), acidified peanut shell (APS), rice husks (RHs), acidified rice husks (ARHs), and a commonly used synthetic carrier, ceramsite (C), were used to support periphyton attachment and growth. The results show that the modified carriers have more hydrophilic groups, higher periphyton biomass, and autotrophic indices than the unmodified carriers. As a consequence, they promote the metabolic versatility of periphyton microbial communities. Thus, the periphyton attached to modified agro-wastes (DPS, APS, and ARH) grew in a stable and sustainable manner. This study suggests that modified PS and RH are effective and environmentally benign carriers that enhance periphyton activity and functionality. Development of periphytic carriers using agro-wastes is also a sustainable method of reusing these materials.

Functional groups characteristics of EPS in biofilm growing on different carriers

This study investigated extracellular polymeric substances (EPSs), including soluble EPS, loosely bound EPS and tightly bound EPS (TB-EPS), in biofilms growing on different carriers from a CANON system to elucidate their different compositions and characteristics. The zeta potentials of all EPS fractions of the two samples were decreased systematically. The soft combination packing (SCP) was more hydrophilic than activated carbon fiber (ACF), and it obtained a significantly higher biomass. However, Raman spectroscopy and Fourier transform infrared spectroscopy revealed the same EPS fraction had similar functional groups between two carriers. Especially for the TB-EPS, total amount and the contents of proteins and polysaccharides in the SCP sample were much higher than those in the ACF sample. Moreover, the TB-EPS fraction of the SCP sample had better bioflocculation activity compared with that of the ACF sample. Therefore the result demonstrated that the characteristics of EPS varied from carrier to carrier.

Joint-action of antifouling substances in copper-free paints

Due to the environmentally harmful impact of tributyltin self-polishing paints, there is a critical need of more ecological alternatives. The aim of the present work is to study the joint-action of three molecules chosen in order to combine the two modes of prevention: chemical and physical repelling of biofouling. This "hybrid" system is principally dedicated to disturb durable settlement of microfouling. Each component was chosen according to its specific properties: chlorhexidine is a bisdiguanide antiseptic with antibacterial activity, zinc peroxide is an inorganic precursor of high instable entities which react with seawater to create hydrogen peroxide, Tween 85 is a non ionic surfactant disturbing interactions between colonizing organisms and surface. Obtained results highlighted the interest on mixing such molecules to get additive action on antifouling efficiency.