Rational Design of Artificial Biofilms as Sustainable Supports for Whole-Cell Catalysis Through Integrating Extra- and Intracellular Catalysis

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.

One-pot enantioselective synthesis of chiral phenyllactic acids by combining stereocomplementary d- and l-lactate dehydrogenases with multi-enzyme expression fine-tuning

Chiral phenyllactic acid (PLA) is a new type of antiseptic agent and a valuable precursor for active ingredients in pharmaceuticals and agrochemicals. In this study, we designed a multi-enzyme cascade that combined stereocomplementary d- and l-lactate dehydrogenases with threonine aldolase, phenylserine dehydratase, and formate dehydrogenase for the one-pot conversion of achiral glycine and benzaldehyde to synthesize d-PLA and l-PLA. To overcome the imbalance of multi-enzymes in a single cell, two enzyme modules, overexpressing four enzymes, were assembled in Escherichia coli cells to construct whole-cell catalysis systems (WCCSs). Furthermore, by optimizing reaction conditions and components, recombinant E. coli (WCCS 26) was able to produce 100 mM d-PLA with >99 % ee using a fed-batch strategy, while E. coli (WCCS 60) produced 47.2 mM l-PLA with >99 % ee. This study presents a sustainable and efficient method for synthesizing chiral PLAs from food-grade achiral starting materials.

Microbial biofilms as a platform for diverse biocatalytic applications

Microbial biofilms have gained significant traction in commercial wastewater treatment due to their inherent resilience, well-organized structure, and potential for collaborative metabolic processes. As our understanding of their physiology deepens, these living catalysts are finding exciting applications beyond wastewater treatment, including the production of bulk and fine chemicals, bioelectricity generation, and enzyme immobilization. While the biological applications of biofilms in different biocatalytic systems have been extensively summarized, the applications of artificially engineered biofilms were rarely discussed. This review aims to bridge this gap by highlighting the untapped potential of engineered microbial biofilms in diverse biocatalytic applications, with a focus on strategies for biofilms engineering. Strategies for engineering biofilm-based systems will be explored, including genetic modification, synthetic biology approaches, and targeted manipulation of biofilm formation processes. Finally, the review will address key challenges and future directions in developing robust biofilm-based biocatalytic platforms for large-scale production of chemicals, pharmaceuticals, and biofuels.

Precision Engineering of the Co-immobilization of Enzymes for Cascade Biocatalysis

The design and orderly layered co-immobilization of multiple enzymes on resin particles remain challenging. In this study, the SpyTag/SpyCatcher binding pair was fused to the N-terminus of an alcohol dehydrogenase (ADH) and an aldo-keto reductase (AKR), respectively. A non-canonical amino acid (ncAA), p-azido-L-phenylalanine (p-AzF), as the anchor for covalent bonding enzymes, was genetically inserted into preselected sites in the AKR and ADH. Employing the two bioorthogonal counterparts of SpyTag/SpyCatcher and azide-alkyne cycloaddition for the immobilization of AKR and ADH enabled sequential dual-enzyme coating on porous microspheres. The ordered dual-enzyme reactor was subsequently used to synthesize (S)-1-(2-chlorophenyl)ethanol asymmetrically from the corresponding prochiral ketone, enabling the in situ regeneration of NADPH. The reactor exhibited a high catalytic conversion of 74 % and good reproducibility, retaining 80 % of its initial activity after six cycles. The product had 99.9 % ee, which that was maintained in each cycle. Additionally, the double-layer immobilization method significantly increased the enzyme loading capacity, which was approximately 1.7 times greater than that of traditional single-layer immobilization. More importantly, it simultaneously enabled both the purification and immobilization of multiple enzymes on carriers, thus providing a convenient approach to facilitate cascade biocatalysis.

Beneficial applications of biofilms

Many microorganisms live in the form of a biofilm. Although they are feared in the medical sector, biofilms that are composed of non-pathogenic organisms can be highly beneficial in many applications, including the production of bulk and fine chemicals. Biofilm systems are natural retentostats in which the biocatalysts can adapt and optimize their metabolism to different conditions over time. The adherent nature of biofilms allows them to be used in continuous systems in which the hydraulic retention time is much shorter than the doubling time of the biocatalysts. Moreover, the resilience of organisms growing in biofilms, together with the potential of uncoupling growth from catalytic activity, offers a wide range of opportunities. The ability to work with continuous systems using a potentially self-advancing whole-cell biocatalyst is attracting interest from a range of disciplines, from applied microbiology to materials science and from bioengineering to process engineering. The field of beneficial biofilms is rapidly evolving, with an increasing number of applications being explored, and the surge in demand for sustainable and biobased solutions and processes is accelerating advances in the field. This Review provides an overview of the research topics, challenges, applications and future directions in beneficial and applied biofilm research.

Engineered Escherichia coli Consortia Function in a Programmable Pattern for Multiple Enzymatic Biosynthesis

Coordinating microbial consortia to realize complex synthetic pathways is an area of great interest in the rapidly growing field of biomanufacturing. This work presents a programmable method for assembling living cells based on the surface display of affinity groups, enabling whole-cell catalysis with optimized catalytic efficiency through the rational arrangement of cell assemblies and enzymes. In the context of d-phenyllactic acid (d-PLA) synthesis, four enzymes were rationally arranged considering substrate channeling and protein expression levels. The production efficiencies of d-PLA catalyzed by engineered microbial consortia were 1.31- and 2.55-fold higher than those of biofilm and whole-cell catalysts, respectively. Notably, substrate channeling was identified between the coimmobilized rate-limiting enzymes, resulting in a 3.67-fold improvement in catalytic efficiency compared with hybrid catalysts (free enzymes coupled with whole-cell catalysts). The highest yield of d-PLA catalyzed by microbial consortia was 102.85 ± 3.39 mM with 140 mM benzaldehyde as the substrate. This study proposes a novel approach to cell enzyme assembly for coordinating microbial consortia in multiple enzymatic biosynthesis processes.

Biotechnological applications of biofilms formed by osmotolerant and halotolerant yeasts

Many microorganisms are capable of developing biofilms under adverse conditions usually related to nutrient limitation. They are complex structures in which cells (in many cases of different species) are embedded in the material that they secrete, the extracellular matrix (ECM), which is composed of proteins, carbohydrates, lipids, and nucleic acids. The ECM has several functions including adhesion, cellular communication, nutrient distribution, and increased community resistance, this being the main drawback when these microorganisms are pathogenic. However, these structures have also proven useful in many biotechnological applications. Until now, the most interest shown in these regards has focused on bacterial biofilms, and the literature describing yeast biofilms is scarce, except for pathological strains. Oceans and other saline reservoirs are full of microorganisms adapted to extreme conditions, and the discovery and knowledge of their properties can be very interesting to explore new uses. Halotolerant and osmotolerant biofilm-forming yeasts have been employed for many years in the food and wine industry, with very few applications in other areas. The experience gained in bioremediation, food production and biocatalysis with bacterial biofilms can be inspiring to find new uses for halotolerant yeast biofilms. In this review, we focus on the biofilms formed by halotolerant and osmotolerant yeasts such as those belonging to Candida, Saccharomyces flor yeasts, Schwannyomyces or Debaryomyces, and their actual or potential biotechnological applications. KEY POINTS: • Biofilm formation by halotolerant and osmotolerant yeasts is reviewed. • Yeasts biofilms have been widely used in food and wine production. • The use of bacterial biofilms in bioremediation can be expanded to halotolerant yeast counterparts.