Biofilm development of Bacillus thuringiensis on MWCNT buckypaper: Adsorption-synergic biodegradation of phenanthrene

Environmental applications and risks of engineered nanomaterials in removing petroleum oil in soil

Oil-contaminated soil posed serious threats to the ecosystems and human health. The unique and tunable properties of engineered nanomaterials (ENMs) enable new technologies for removing and repairing oil-contaminated soil. However, few studies systematically examined the linkage between the change of physicochemical properties and the removal efficiency and environmental functions (e.g., potential risk) of ENMs, which is vital for understanding the ENMs environmental sustainability and utilization as a safety product. Thus, this review briefly summarized the environmental applications of ENMs to removing petroleum oil from complex soil systems: Theoretical and practical fundamentals (e.g., excellent physicochemical properties, environmental stability, controlled release, and recycling technologies), and various ENMs (e.g., iron-based, carbon-based, and metal oxides nanomaterials) remediation case studies. Afterward, this review highlights the removing mechanism (e.g., adsorption, photocatalysis, oxidation/reduction, biodegradation) and the impact factor (e.g., nanomaterials species, natural organic matter, and soil matrix) of ENMs during the remediation process in soil ecosystems. Both positive and negative effects of ENMs on terrestrial organisms have been identified, which are mainly derived from their diverse physicochemical properties. In linking nanotechnology applications for repairing oil-contaminated soil back to the physical and chemical properties of ENMs, this critical review aims to raise the research attention on using ENMs as a fundamental guide or even tool to advance soil treatment technologies.

Microbes and microbial strategies in carcinogenic polycyclic aromatic hydrocarbons remediation: a systematic review

Degradation, detoxification, or removal of the omnipresent polycyclic aromatic hydrocarbons (PAHs) from the ecosphere as well as their prevention from entering into food chain has never appeared simple. In this context, cost-effective, eco-friendly, and sustainable solutions like microbe-mediated strategies have been adopted worldwide. With this connection, measures have been taken by multifarious modes of microbial remedial strategies, i.e., enzymatic degradation, biofilm and biosurfactant production, application of biochar-immobilized microbes, lactic acid bacteria, rhizospheric-phyllospheric-endophytic microorganisms, genetically engineered microorganisms, and bioelectrochemical techniques like microbial fuel cell. In this review, a nine-way directional approach which is based on the microbial resources reported over the last couple of decades has been described. Fungi were found to be the most dominant taxa among the CPAH-degrading microbial community constituting 52.2%, while bacteria, algae, and yeasts occupied 37.4%, 9.1%, and 1.3%, respectively. In addition to these, category-wise CPAH degrading efficiencies of each microbial taxon, consortium-based applications, CPAH degradation-related molecular tools, and factors affecting CPAH degradation are the other important aspects of this review in light of their appropriate selection and application in the PAH-contaminated environment for better human-health management in order to achieve a sustainable ecosystem.

Understanding the role of graphene oxide in affecting PAHs biodegradation by microorganisms: An integrated analysis using 16SrRNA, metatranscriptomic, and metabolomic approaches

Graphene oxide (GO)-promoted microbial degradation technology is considered an important strategy to eliminate polycyclic aromatic hydrocarbons (PAHs) in the environment; however, the mechanism by which GO affects microbial degradation of PAHs has not been fully studied. Thus, this study aimed to analyze the effect of GO-microbial interaction on PAHs degradation at the microbial community structure, community gene expression, and metabolic levels using multi-omics combined technology. We treated PAHs-contaminated soil samples with different concentrations of GO and analyzed the soil samples for microbial diversity after 14 and 28 days. After a short exposure, GO reduced the diversity of soil microbial community but increased potential degrading microbial abundance, promoting PAHs biodegradation. This promotion effect was further influenced by the GO concentration. In a short period of time, GO upregulated the expression of genes involved in microbial movement (flagellar assembly), bacterial chemotaxis, two-component system, and phosphotransferase system in the soil microbial community and increased the probability of microbial contact with PAHs. Biosynthesis of amino acids and carbon metabolism of microorganisms were accelerated, thereby increasing the degradation of PAHs. With the extension of time, the degradation of PAHs stagnated, which may be due to the weakened stimulation of GO on microorganisms. The results showed that screening specific degrading microorganisms, increasing the contact area between microorganisms and PAHs, and prolonging the stimulation of GO on microorganisms were important means to improve the biodegradation efficiency of PAHs in soil. This study elucidates how GO affects microbial PAHs degradation and provides important insights for the application of GO-assisted microbial degradation technology.

Effects of combined remediation of pre-ozonation and bioaugmentation on degradation of benzo[a]pyrene and microbial community structure in soils

The combination technique of pre-ozonation and bioaugmentation is promising for remediating benzo[a]pyrene (BaP)-contaminated soil. However, little is known about the effect of coupling remediation on the soil biotoxicity, soil respiration, enzyme activity, microbial community structure, and microbial in the process of remediation. This study developed two coupling remediation strategies (pre-ozonation coupled with bioaugmentation by addition of polycyclic aromatic hydrocarbons (PAHs) specific degrading bacteria or activated sludge), compared with sole ozonation and sole bioaugmentation, to improve degradation of BaP and recovery of soil microbial activity and community structure. Results showed that the higher removal efficiency of BaP (92.69-93.19%) was found in coupling remediation, compared with sole bioaugmentation (17.71-23.28%). Meanwhile, coupling remediation significantly reduced the soil biological toxicity, promoted the rebound of microbial counts and activity, and recovered the species numbers and microbial community diversity, compared with sole ozonation and sole bioaugmentation. Besides, it was feasible to replace microbial screening with activated sludge, and coupling remediation by addition of activated sludge was more conducive to the recovery of soil microbial communities and diversity. This work provides a strategy of pre-ozonation coupled with bioaugmentation to further degrade BaP in soil by promoting the rebound of microbial counts and activity, as well as the recovery of species numbers and microbial community diversity.

UV stabilizers can foster early development of biofilms on freshwater microplastics

Interactions between microbes and microplastics are important as of emerging plastic loads in the global environment. Although diverse plastic additives are used in large amounts, there are very few studies on a quantitative comparison of plastisphere on plastics with different plastic additives. We studied the effects of two widely used UV stabilizers (benzotriazole-type UV-327 and benzophenone-type UV-531 were selected based on their persistence and toxicity) in low-density polyethylene (LDPE) on freshwater microbes. This is the first study on the sole effects of UV stabilizers used as plastic additives on freshwater in situ plastisphere biofilm development. Confocal laser scanning microscopy, assisted with proper differentiating fluorochromes and threshold-based 3D segmentation of data, was used to visualize and quantify biofilm. On the first week of biofilm growth, there was very little biovolume and a negligible amount of phototrophs on pristine LDPE contrasting other substrates. Biovolumes were significantly higher on LDPE with UV stabilizers (up to 159% higher than pristine LDPE), although the biomass was mostly dead due to toxicity (>100% higher dead biovolume than live biovolume in LDPE with UV stabilizers). After the fourth week, marginally higher biovolumes along with a revival of the biomass on LDPE with UV stabilizers were observed. The ability to induce microorganismic intracellular reactive oxygen species by UV stabilizers was detected, which may stimulate biofilm growth during the primary phase of biofilm development. Atomic force microscopy analysis denoted that LDPE with UV stabilizers exhibit considerably stronger adhesion force than pristine LDPE. These observations suggest that UV stabilizers can foster the early attachment of microbes to microplastics while killing the surface contacting layer. An alive upper layer of microbes can get developed on the dead biofilm without much disruption due to the toxicity of UV stabilizers. This occurrence can eventually boost the early development of biofilms on plastics.

Adhesion of Rhodococcus bacteria to solid hydrocarbons and enhanced biodegradation of these compounds

Adhesive activities of hydrocarbon-oxidizing Rhodococcus bacteria towards solid hydrocarbons, effects of adhesion on biodegradation of these compounds by rhodococcal cells and adhesion mechanisms of Rhodococcus spp. were studied in this work. It was shown that efficiency of Rhodococcus cells' adhesion to solid n-alkanes and polycyclic aromatic hydrocarbons (PAHs) varied from 0.0 to 10.6·10⁶ CFU/cm². R. erythropolis IEGM 212 and R. opacus IEGM 262 demonstrated the highest (≥ 4.3·10⁶ CFU/cm²) adhesion. The percentage biodegradation of solid hydrocarbons (n-hexacosane and anthracene as model substrates) by Rhodococcus cells was 5 to 60% at a hydrocarbon concentration of 0.2% (w/w) after 9 days and strongly depended on cell adhesive activities towards these compounds (r ≥ 0.71, p < 0.05). No strict correlation between the adhesive activities of rhodococcal cells and physicochemical properties of bacteria and hydrocarbons was detected. Roughness of the cell surface was a definitive factor of Rhodococcus cell adhesion to solid hydrocarbons. Specific appendages with high adhesion force (≥ 0.6 nN) and elastic modulus (≥ 6 MPa) were found on the surface of Rhodococcus cells with high surface roughness. We hypothesized that these appendages participated in the adhesion process.

Biofilm development of Bacillus siamensis ATKU1 on pristine short chain low-density polyethylene: A case study on microbe-microplastics interaction

A low-density polyethylene (LDPE) degrading bacterial strain (ATKU1) was isolated (99.86% similar with Bacillus siamensis KCTC 13613^T) from a plastic dumping site to study interactions between microplastics (< 5 mm) and microorganisms. The strain was found (by scanning electron microscopy) to form biofilm on the microplastic surface after its interaction with LDPE (avg. M_w~4,000 Da and avg. M_n~1,700 Da) as a sole carbon source. Atomic force microscopy (AFM) showed the biofilm's 3-D developmental patterns and significantly increased Young's modulus of the LDPE surface after microbial treatment. Most of the viable bacteria attached to biofilms rather than media, which suggested their ability to utilize LDPE. Absorption bands of carbonyl, alkenyl, acyl, ester, primary-secondary alcohol, alkene groups and nitric oxides were found on the treated LDPE particles using Fourier-transform infrared spectroscopy. Fourier transform-ion cyclotron resonance mass spectrometry of the media indicated compositional shifts of the compounds after treatment (i.e., increase in the degree of unsaturation and increment in oxygen-to-carbon ratio) and presence of unsaturated hydrocarbons, polyketides, terpenoids, aliphatic/peptides, dicarboxylic acids, lipid-like compounds were hinted. The plastic degrading abilities of Bacillus siamensis ATKU1 suggest its probable application for large scale plastic bioremediation facility.

Viability and distribution of bacteria immobilized on Sawdust@silica: The removal mechanism of phenanthrene in soil

Immobilized cells (ICs) have been widely used to enhance the remediation of organic-contaminated soil (e.g., polycyclic aromatic hydrocarbons, PAHs). Once ICs are added to the heterogeneous soil, degradation hotspots are immediately formed near the carrier, leaving the remaining soil lack of degrading bacteria. Therefore, it remains unclear how ICs efficiently utilize PAHs in soil. In this study, the viability of Silica-IC (Cells@Sawdust@Silica) and the distribution of inoculated ICs and phenanthrene (Phe) in a slurry system (soil to water ratio 1:2) were investigated to explore the removal mechanism of PAHs by the ICs. Results showed that the Silica-IC maintained (i) good reproductive ability (displayed by the growth curve in soil and water phase), (ii) excellent stability, which was identified by the ratio of colony forming units in the soil phase to the water phase, the difference between the colony number and the DNA copies, and characteristics of the biomaterial observed by the FESEM, and (iii) high metabolic activity (the removal percentages of Phe in soil by the ICs were more than 95% after 48 h). Finally, the possible pathways for the ICs to efficiently utilize Phe in soil are proposed based on the distribution and correlation of Phe and ICs between the soil and water phase. The adsorption-degradation process was dominant, i.e., the enhanced degradation occurred between the ICs and carrier-adsorbed Phe. This study provided new insights on developing a bio-material for efficient bio-remediation of PAHs-contaminated soil.

Degradation of several polycyclic aromatic hydrocarbons by laccase in reverse micelle system

Remediation of polycyclic aromatic hydrocarbons (PAHs) in oily sludge has become the focus of attention. UV spectrophotometer analysis showed that four types of PAHs were found in sample, which including phenanthrene, anthracene, benzo(a)anthracene and benzo(b)fluoranthene. In order to degrade PAH effectively, the laccase reverse micelles system was proposed. The system protects laccase from being affected by organic phase. Reverse micelles were prepared by using isooctane to simulate oil. The optimum water content W₀ was 10 by measuring the electrical conductivity of the system. Under this condition, the effects of pH, temperature and ionic strength on the degradation rate of PAHs were investigated. Also, compared with that of non-immobilized laccase, the ratio between the secondary structures of laccase under different conditions was studied. The results showed that the highest laccase activity was obtained at pH 4.2 and 30 °C with 60 mmol/L KCl. Meanwhile, the structure of α-helix accounts for the largest proportion, and the ratio of α-helix in the laccase secondary structure in the laccase-reverse micelle system was higher than that of the non-immobilized one under this condition. Finally, predicting the reactive site of the degradation of polycyclic aromatic hydrocarbons was simulated by ORCA (Version 4.2.0). The application in oily sludge was further conducted. This study provides an effective method and basis for the degradation of PAHs in oily sludge.

Molecular Recognition and Cell Surface Biochemical Response of Bacillus thuringiensis on Triphenyltin

Triphenyltin (TPT) has severely polluted the environment, and it often coexists with metal ions, such as Cu2+. This paper describes the cell’s molecular recognition of TPT, the interaction between TPT recognition and Cu2+ biosorption, and their effect on cell permeability. We studied the recognition of TPT by Bacillus thuringiensis cells and the effect of TPT recognition on Cu2+ biosorption by using atomic force microscopy to observe changes in cell surface mechanical properties and cellular morphology and by using flow cytometry to determine the cell growth status and cell permeability. The results show that B. thuringiensis can quickly recognize different media. The adhesion force of cells in contact with Tween 80 was significantly reduced to levels that were much lower than that of cells in contact with PBS. Conversely, the cell surface adhesion force increased as TPT became more degraded. B. thuringiensis cells maintained their original morphology after 48 h of TPT treatment. The amount of Cu2+ adsorption by TPT-treated cells was positively correlated with the surface adhesion force (r = 0.966, P = 0.01). The cell adhesion force significantly decreased after Cu2+ adsorption, and cell recognition of TPT and/or Cu2+ hindered the entrance of 2’,7’-dichlorodihydrofluorescein diacetate (DCFH-DA) into the cell. The initial diffusion time of DCFH-DA into cells treated by PBS, Cu2+, TPT, and TPT+Cu2+ was 4, 10, 30, and 30 min, respectively, and the order of the fluorescence intensity was PBS >> Cu2+ > TPT > TPT+Cu2+. We conclude that changes in the cell surface properties of the microbe during recognition of pollutants depend on the contaminant’s properties. B. thuringiensis recognized TPT and secreted intracellular substances that not only enhanced the adsorption of Cu2+, but also formed a “barrier” on the cell surface that reduced permeability. These findings provide a novel insight into the mechanism of microbial removal of pollutants.