Display of a novel carboxylesterase CarCby on Escherichia coli cell surface for carbaryl pesticide bioremediation

Engineering an Escherichia coli surface display platform based on an autotransporter from Stenotrophomonas maltophilia: Autodisplay of enzymes with low to high molecular weight

Surface display technology has garnered significant attention for preparing efficient whole cell catalysts, while reported carrier proteins still cannot meet the demand to display various passenger domains, especially for those with high molecular weight. This study demonstrates that the autotransporter of esterase Est7 (E7AT) from Stenotrophomonas maltophilia played a decisive role in its efficient surface display. Guided by the original signal peptide, the surface display ratio of Est7 was determined as 89.67% with the total enzymatic activity of 16.67U/mL, which was much higher than 4.60U/mL and 5.70U/mL for the signal peptides derived from pectolase B (pelB) and cholera toxin B (ctxB), respectively. Then, the E7AT unit was successfully developed to surface display proteins with varying molecular weight from 19.3kDa to 117.9kDa, showing a more effective autodisplay ability than adhesin involved in diffuse adherence (AIDA-I), ice nucleation proteins (InaK and InaP), and outer membrane proteins (lipoprotein/ompA, MltA-interacting protein A, and yiaT) systems. Additionally, a galactosidase (GAL) displayed by E7AT was employed to hydrolyze lactose, achieving a promising hydrolysis rate of 31.63% in 2h. The displayed GAL retained 63.24% and 41.41% activity in third and sixth batch, respectively, indicating the considerable potential of E7AT in developing efficient whole cell catalysts.

Yeast surface display technology: Mechanisms, applications, and perspectives

Microbial cell surface display technology, which relies on genetically fusing heterologous target proteins to the cell wall through fusion with cell wall anchor proteins, has emerged as a promising and powerful method with diverse applications in biotechnology and biomedicine. Compared to classical intracellular or extracellular expression (secretion) systems, the cell surface display strategy stands out by eliminating the necessity for enzyme purification, overcoming substrate transport limitations, and demonstrating enhanced activity, stability, and selectivity. Unlike phage or bacterial surface display, the yeast surface display (YSD) system offers distinct advantages, including its large cell size, ease of culture and genetic manipulation, the use of generally regarded as safe (GRAS) host cell, the ability to ensure correct folding of complex eukaryotic proteins, and the potential for post-translational modifications. To date, YSD systems have found widespread applications in protein engineering, waste biorefineries, bioremediation, and the production of biocatalysts and biosensors. This review focuses on detailing various strategies and mechanisms for constructing YSD systems, providing a comprehensive overview of both fundamental principles and practical applications. Finally, the review outlines future perspectives for developing novel forms of YSD systems and explores potential applications in diverse fields.

Laccase surface-display for environmental tetracycline removal: From structure to function

Facing the increasingly prominent tetracycline pollution and the resulting environmental problems, how to find environmental and efficient treatment means is one of the current research hotspots. In this study, the laccase surface-display technology for tetracycline treatment was investigated. Via study, the type of anchoring protein had a minor influence on the laccase ability, while the type of laccase showed a major impact. Bacillus subtilis spore coat protein (CotA) exhibited higher laccase activity, stability, and efficiency in degrading tetracycline than Pleurotus ostreatus laccase 6 (Lacc6). The superiority of bacterial laccase over fungal laccase was elucidated from the perspective of crystal structure. Besides, a variety of technical means were used to verify the success of surface-display. pGSA-CotA surface-displayed bacteria exhibited good tolerance to high temperature, pH, and various heavy metals. Importantly, surface-displayed bacteria showed faster degradation efficiency and better treatment effects than the intracellular expression bacteria in tetracycline degradation. This implies that surface display technology has greater potential for laccase-mediated environmental remediation. Due to the adverse impacts of tetracycline on soil enzyme activity and microorganisms, our study found that pGSA-CotA surface-displayed bacteria can alleviate tetracycline stress in soil and partially activate the soil, thereby increasing soil enzyme activity and certain nitrogen cycling genes.

Anchorless Bacterial Moonlighting Metabolic Enzymes Modulate the Immune System and Contribute to Pathogenesis

Moonlighting proteins (MPs), characterized by their ability to perform multiple physiologically unrelated functions without alterations to their primary structures, represent a fascinating class of biomolecules with significant implications for host-pathogen interactions. This Review highlights the emerging importance of metabolic moonlighting proteins (MetMPs) in bacterial pathogenesis, focusing on their non-canonical secretion and unconventional surface anchoring mechanisms. Despite lacking typical signal peptides and anchoring motifs, MetMPs such as acetaldehyde alcohol dehydrogenase (AdhE) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) are secreted and localized to the bacterial surface under stress conditions, facilitating host colonization and immune evasion. The secretion of MetMPs, often observed during conditions such as resource scarcity or infection, suggests a complex regulation akin to the overexpression of heat shock proteins in response to environmental stresses. This Review proposes two potential pathways for MetMP secretion: membrane damage-induced permeability and co-transportation with traditionally secreted proteins, highlighting a remarkable bacterial adaptability. Biophysically, surface anchoring of MetMPs is driven by electrostatic interactions, bypassing the need for conventional anchoring sequences. This mechanism is exemplified by the interaction between the bifunctional enzyme AdhE (known as Listeria adhesion protein, LAP) and the internalin B (InlB) in Listeria monocytogenes, which is mediated by charged residues facilitating adhesion to host tissues. Furthermore, MetMPs play critical roles in iron homeostasis, immune modulation, and evasion, underscoring their multifaceted roles in bacterial pathogenicity. The intricate dynamics of MetMP secretion and anchoring underline the need for further research to unravel the molecular mechanisms underpinning these processes, offering potential new targets for therapeutic intervention against bacterial infections.

Surface expression of carbonic anhydrase on E. coli as a sustainable approach for enzymatic CO2 capture

The utilisation of carbonic anhydrase (CA) in CO2 sequestration is becoming prominent as an efficient, environment friendly and rapid catalyst for capturing CO2 from industrial emissions. However, the application of CA enzyme in soluble form is constrained due to its poor stability in operational conditions of CO2 capture and also production cost of the enzyme. Addressing these limitations, the present study focuses on the surface display of CA from Bacillus halodurans (BhCA) on E coli aiming to contribute to the cost-effectiveness of carbon capture through CA technology. This involved the fusion of the BhCA-encoding gene with the adhesion molecule involved in diffuse adherence (AIDA-I) autotransporter, resulting in the efficient display of BhCA (595 ± 60 U/gram dry cell weight). Verification of the surface display of BhCA was accomplished by conjugating with FITC labelled anti-his antibody followed by fluorescence-activated cell sorting (FACS) and cellular fractionation in conjunction with zymography. Biochemical characterisation of whole-cell biocatalyst revealed a noteworthy enhancement in thermostability, improvement in the thermostability with T1/2 of 90 ± 1.52 minutes at 50 ˚C, 36 ± 2.51 minutes at 60 ˚C and18 ± 1.52 minutes at 80˚C. Surface displayed BhCA displayed remarkable reusability retaining 100% activity even after 15 cycles. Surface displayed BhCA displayed highly alkali stable nature like free counterpart in solution. The alkali stability of the surface-displayed BhCA was comparable to its free counterpart in solution. Furthermore, the study investigated the impact of different metal ions, modulators, and detergents on the whole-cell biocatalysts. The present work represents the first report on surface display of CA utilising the AIDA-1 autotransporter.

Construction of Cupriavidus necator displayed with superoxide dismutases for enhanced growth in bioelectrochemical systems

It is of great significance to utilize CO2 as feedstock to synthesize biobased products, particularly single cell protein (SCP) as the alternative food and feed. Bioelectrochemical system (BES) driven by clean electric energy has been regarded as a promising way for Cupriavidus necator to produce SCP from CO2 directly. At present, the key problem of culturing C. necator in BES is that reactive oxygen species (ROS) generated in cathode chamber are harmful to bacterial growth. Therefore, it is necessary to find a solution to mitigate the negative effect of ROS. In this study, we constructed a number of C. necator strains displayed with superoxide dismutase (SOD), which allowed the decomposition of superoxide anion radical. The effects of promoters and signal peptides on the cell surface displayed SOD were analyzed. The proteins displayed on the surface were further verified by the fluorescence experiment. Finally, the growth of C. necator CMS incorporating a pBAD-SOD-E-tag-IgAβ plasmid could achieve 4.9 ± 1.0 of OD600 by 7 days, equivalent to 1.7 ± 0.3 g/L dry cell weight (DCW), and the production rate was 0.24 ± 0.04 g/L/d DCW, around 2.7-fold increase than the original C. necator CMS (1.8 ± 0.3 of OD600). This study can provide an effective and novel strategy of cultivating strains for the production of CO2-derived SCP or other chemicals in BES.

Degradation strategies of pesticide residue: From chemicals to synthetic biology

The past 50 years have witnessed a massive expansion in the demand and application of pesticides. However, pesticides are difficult to be completely degraded without intervention hence the pesticide residue could pose a persistent threat to non-target organisms in many aspects. To aim at the problem of the abuse of pesticide products and excessive pesticide residues in the environment, chemical and biological degradation methods are widely developed but are scaled and insufficient to solve such a pollution. In recent years, bio-degradative tools instructed by synthetic biological principles have been further studied and have paved a way for pesticide degradation. Combining the customized design strategy and standardized assembly mode, the engineering bacteria for multi-dimensional degradation has become an effective tool for pesticide residue degradation. This review introduces the mechanisms and hazards of different pesticides, summarizes the methods applied in the degradation of pesticide residues, and discusses the advantages, applications, and prospects of synthetic biology in degrading pesticide residues.