Surface display of lipolytic enzyme, Lipase A and Lipase B of Bacillus subtilis on the Bacillus subtilis spore

Implementation of Spore Display in Paenibacillus polymyxa with Different Hydrolytic Enzymes

Biotechnological processes are essential for producing climate-friendly high-value chemicals or pharmaceutical compounds, which can include steps catalyzed by enzymes. Therefore, establishing new, robust, and cheap enzyme production processes is desirable. One possible way to enhance processes is through the use of the spore display method. Spore display can present heterologous proteins on the surface of bacterial spores, offering numerous advantages in a range of biotechnological applications. This study demonstrates the implementation of the spore display method in Paenibacillus polymyxa, achieved by modifying the spore surface, incorporating an anchoring protein, and attaching green fluorescent protein to it, allowing the visualization of fluorescent spores. Following the initial experiment, a native lipase (Lip3), a heterologous lipase (LipA) from Bacillus subtilis, a native esterase (PnbA) from P. polymyxa, and a lipoyl synthase were expressed during sporulation and displayed on the spore surface. The activity profiles were determined in the temperature range from 4 °C to 70 °C. The PnbA reached its optimum at 4 °C, whereas the LipA from B. subtilis showed 4.4-fold higher activity at 42 °C compared to the control. Furthermore, we explored a possible new technique for the purification of enzymes with the TEV cleavage site between the anchor and the protein of interest. Finally, we showed a not-yet-described side activity of the lipoyl synthase over a wide temperature range.

Stress-Tolerant, Recyclable, and Renewable Biocatalyst Platform Enabled by Engineered Bacterial Spores

Here, we describe a stress-tolerant, recyclable, and renewable biocatalyst platform based on T7 RNA polymerase-enabled high-density protein display on bacterial spores (TIED). TIED uses high-level T7 RNA polymerase-driven expression of recombinant proteins specifically in sporulating cells to allow spontaneous assembly of recombinant fusion proteins on the Bacillus subtilis spore surface. TIED enables high loading density in the range of 10⁶ to 10⁷ recombinant enzymes per spore, robust catalytic activity of displayed enzymes comparable to the respective free enzymes, and enhanced kinetic stability of displayed enzymes in methanol and elevated temperatures. Furthermore, we demonstrate TIED enzymes to be not only recyclable but also fully renewable after the loss of activity through induction of germination and sporulation, enabling perpetual regeneration of these immobilized biocatalysts.

Metabolic engineering of Escherichia coli for efficient biosynthesis of butyl acetate

Background

Butyl acetate is a versatile compound that is widely used in the chemical and food industry. The conventional butyl acetate synthesis via Fischer esterification of butanol and acetic acid using catalytic strong acids under high temperature is not environmentally benign. Alternative lipase-catalyzed ester formation requires a significant amount of organic solvent which also presents another environmental challenge. Therefore, a microbial cell factory capable of producing butyl acetate through fermentation of renewable resources would provide a greener approach to butyl acetate production.

Result

Here, we developed a metabolically engineered strain of Escherichia coli that efficiently converts glucose to butyl acetate. A modified Clostridium CoA-dependent butanol production pathway was used to synthesize butanol which was then condensed with acetyl-CoA through an alcohol acetyltransferase. Optimization of alcohol acetyltransferase expression and redox balance with auto-inducible fermentative controlled gene expression led to an effective titer of 22.8 ± 1.8 g/L butyl acetate produced in a bench-top bioreactor.

Conclusion

Building on the well-developed Clostridium CoA-dependent butanol biosynthetic pathway, expression of an alcohol acetyltransferase converts the butanol produced into butyl acetate. The results from this study provided a strain of E. coli capable of directly producing butyl acetate from renewable resources at ambient conditions.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01755-y.

Expression of d-psicose-3-epimerase from Clostridium bolteae and Dorea sp. and whole-cell production of d-psicose in Bacillus subtilis

Purpose

d-psicose-3-epimerase (DPEase) catalyses the isomerisation of d-fructose to d-psicose, a rare sugar in nature with unique nutritional and biological functions. An effective industrial-scale method is needed for d-psicose production. Herein, the expression of a neutral and a slightly acidic pH DPEase in Bacillus subtilis was evaluated.

Methods

Two DPEase genes from Clostridium bolteae and Dorea sp. were separately expressed in B. subtilis via plasmid pSTOP1622, and an extra P43 promoter was employed to the expression cassette. The fermentation conditions of the engineered B. subtilis strains were also optimised, to facilitate both cell growth and enzyme production.

Result

The introduction of P43 promoter to the two DPEase genes increased enzyme production by about 20%. Optimisation of fermentation conditions increased DPEase production to 21.90 U/g at 55 °C and 24.01 U/g at 70 °C in B. subtilis expressing C. bolteae or Dorea sp. DPEase, equating to a 94.67% and 369.94% increase, respectively, relative to controls.

Conclusion

Enhanced DPEase production was achieved in B. subtilis expressing C. bolteae or Dorea sp. DPEase genes.

Progress in research and application development of surface display technology using Bacillus subtilis spores

Bacillus subtilis is a widely distributed aerobic Gram-positive species of bacteria. As a tool in the lab, it has the advantages of nonpathogenicity and limited likelihood of becoming drug resistant. It is a probiotic strain that can be directly used in humans and animals. It can be induced to produce spores under nutrient deficiency or other adverse conditions. B. subtilis spores have unique physical, chemical, and biochemical characteristics. Expression of heterologous antigens or proteins on the surface of B. subtilis spores has been successfully performed for over a decade. As an update and supplement to previously published research, this paper reviews the latest research on spore surface display technology using B. subtilis. We have mainly focused on the regulation of spore coat protein expression, display and application of exogenous proteins, and identification of developing research areas of spore surface display technology.

Microbial production of butyl butyrate, a flavor and fragrance compound

Butyl butyrate (BB) has been widely used as a flavor and fragrance compound in the beverage, food, perfume, and cosmetic industries. Currently, BB is produced through two-step processes; butanol and butyrate are first produced and are used as precursors for the esterification reactions to yield BB in the next step. Recently, an alternative process to the current process has been developed by using microorganisms for the one-pot BB production. In the one-pot BB process, alcohol acyl transferases (AATs) and lipases play roles in the esterification of butanol together with their co-substrates butyryl-CoA and butyrate, respectively. In this paper, we review the characteristics of two enzymes including AAT and lipase in the esterification reaction. Also, we review the one-pot processes for BB production by employing the wild-type and engineered Clostridium species and the engineered Escherichia coli strains, with the combination of AATs and lipases.