Evaluation of Feasibility of Using the Bacteriophage T4 Lysozyme to Improve the Hydrolysis and Biochemical Methane Potential of Secondary Sludge

Mitigating methane emission from oil sands tailings using enzymatic and lime treatments

Engineering strategies to reduce greenhouse gases (GHGs) emissions by inhibiting methanogenesis in oil sands tailings have rarely been examined. In this study, we explored the potential impact of chemical treatment (lime) and biological treatment using enzymes (lysozyme and protease) on inhibiting methane emissions from tailings. Overall, treatment with protease 3%, lysozyme 3%, and lime 5000 ppm reduced CH₄ production (by 52%, 28%, and 25%, respectively) and were weakly associated with the archaeal abundance. Enzymes treatment resulted in a higher reduction in CH₄ production compared with lime treatment. A 3% lysozyme treatment suppressed CH₄ production (the change in methane was 0.48 mmol) and reduced the degradation of hexane throughout the experiment. Similarly, 3% protease suppressed CH₄ production throughout the experiment (the change in methane was 0.78 mmol), which could be attributed to the pH reduction to pH 4.9 at week 23 resulting from the formation of volatile fatty acids. Another possible mechanism could be the formation of toxic compounds, such as high nitrogen content, after protease treatment that inhibited the microbial community. The toxicity effect to Vibrio fischeri was greater with lysozyme 3% and protease 3% treatment than with lime treatment (124 TU and 76 TU, respectively). Lime treatment resulted in the highest reduction in 16S rRNA gene copies from 5.7 × 10⁶ cells g^-1 (control) to 2.7 × 10⁵, 1.71 × 10⁵, and 1.4 × 10⁵ cells g^-1 for 1600, 3500, and 5000 ppm treatments, respectively. This study supports further work to examine and determine the optimum conditions (e.g., enzyme and lime dosages) for CH₄ inhibition.

Maximizing electron flux, microbial diversity and gene abundance in MFC powered electro-Fenton system by optimizing co-addition of lysozyme and 2-bromoethanesulfonate

In this study, a microbial fuel cell powered electro-Fenton system (MFCⓅEFs) was established in order to overcome the shortcomings of low electron flux and unexpected methane production, while simultaneously treating excess sludge (ES, substrate) and refractory syringic acid (SA). A strategy of co-adding lysozyme (LZ, as ES degradation catalyst) and 2-bromoethanesulfonate (BES, as methane inhibitor) into ES was optimized in MFCⓅEFs to maximize electron flux, microbial community diversity and functional gene abundance. The removal of sludge total chemical oxygen demand (TCOD) achieved 81.69% in 25 d under an optimal co-addition strategy (40.41 mg/gSS of LZ, 27.03 mmol/L of BES, adding on 22.8 h of the7th day), with a simultaneous high degradation of SA (99.30% in 25 h). Correspondingly, a maximum power density of 3.35 W/m³ was achieved (only 0.62 W/m³ from the control), which effectively realizes in-situ micro-electricity generation and utilization for bioelectric Fenton processes. Moreover, 42.25% of the total charges were employed for bio-electricity generation. The electricigens of Pseudomonas, Acinetobacter and Chlorobium showed effective enrichment, while the abundance of methanogenesis archaea was extremely decreased. Functional genes associated with methanogenesis including mtaA, hdra, and mcrA were effectively inhibited. The life cycle assessment along with an optimized co-addition strategy illustrated a beneficial environmental effect, particularly in terms of ecosystem quality and climate change. Above all, an enhanced synchronous degradation of excess sludge and refractory pollutants had been realized in a green and environmentally friendly way.

Genetically Encoded Biosensor-Based Screening for Directed Bacteriophage T4 Lysozyme Evolution

Lysozyme is widely used as a model protein in studies of structure–function relationships. Recently, lysozyme has gained attention for use in accelerating the degradation of secondary sludge, which mainly consists of bacteria. However, a high-throughput screening system for lysozyme engineering has not been reported. Here, we present a lysozyme screening system using a genetically encoded biosensor. We first cloned bacteriophage T4 lysozyme (T4L) into a plasmid under control of the araBAD promoter. The plasmid was expressed in Escherichia coli with no toxic effects on growth. Next, we observed that increased soluble T4L expression decreased the fluorescence produced by the genetic enzyme screening system. To investigate T4L evolution based on this finding, we generated a T4L random mutation library, which was screened using the genetic enzyme screening system. Finally, we identified two T4L variants showing 1.4-fold enhanced lytic activity compared to native T4L. To our knowledge, this is the first report describing the use of a genetically encoded biosensor to investigate bacteriophage T4L evolution. Our approach can be used to investigate the evolution of other lysozymes, which will expand the applications of lysozyme.