Efficient secreted expression of natural intracellular β-galactosidase from Bacillus aryabhattai via non-classical protein secretion pathway in Bacillus subtilis

pH-Adaptable CuO2 photo-responsive oxidase with phage-lysed β-galactosidase based cascade reaction for colorimetric detection of Escherichia coli in drinking water with high specificity and sensitivity

Escherichia coli (E. coli) is a primary cause of various waterborne diseases. However, detecting E. coli faces challenges in terms of speed, cost, sensitivity, and selectivity, especially in resource-limited regions. In this study, a smartphone-assisted CuO2 and β-galactosidase (β-gal)-mediated cascade colorimetric method for E. coli detection was developed. A pH-adaptable CuO2 acting as a photo-responsive oxidase was synthesized simply and combined with β-gal released from E. coli lysed by bacteriophages, enabling an enzyme-nanozyme cascade reaction. In this reaction, β-gal catalyzes the conversion of p-aminophenyl β-D-galactopyranoside (PAPG) to p-aminophenol (PAP), which subsequently inhibits the photo-responsive oxidase activity of CuO2. The photo-responsive oxidase CuO2, with its unique mechanism to generate holes for 3,3',5,5'-Tetramethylbenzidine (TMB) oxidation, overcomes the typical pH dependency of nanozymes, maintaining the optimal activity of both CuO2 oxidase and β-gal, enhancing sensitivity in the enzyme cascades. Bacteriophages, serving as specific bacterial identifiers, selectively recognize E. coli and promote the β-gal rapid release, further enhancing the detection sensitivity. This method achieves a detection limit of 15 CFU mL-1, accurately measured E. coli concentrations as low as 102 CFU mL-1, exhibited excellent recovery rates, ranging from 95.0 % to 104.1 %, with RSD between 1.3 % and 2.8 %, distinguishes the live and dead E. coli, reducing false positive and negative. Moreover, coupled with a smartphone, the sensor provides swift and accessible colorimetric data analysis, making it ideal for resource-constrained areas. In summary, this method is specific, sensitive, rapid, and cost-effective, requiring no pretreatment and offering broad potentials for bacterial detection in resource-limited areas.

MRI detection of senescent cells in porcine knee joints with a β-galactosidase responsive Gd-chelate

Senescent cells promote osteoarthritis progression through the secretion of inflammatory mediators. Preclinical studies have identified senescence-associated beta-galactosidase (β-gal) as a biomarker of senescence, but in vivo detection remains challenging. Here, we evaluated whether a β-gal responsive gadolinium (Gd) chelate can non-invasively detect β-gal expressing senescent cells with standard clinical magnetic resonance imaging (MRI) technology in vitro, ex vivo, and in vivo in porcine joints. In vitro studies showed that senescent mesenchymal stromal cells (MSCs) exhibited significant MRI signal enhancement upon incubation with the β-gal responsive Gd-chelate compared to viable control cells. In vivo, intraarticular injection of the probe into pig knee joints revealed its retention and activation by senescent cells in cartilage defects, evidenced by a significant increase in R 1 relaxation rate. MRI-based senescent cell detection holds promise for identifying patients amenable to senolytic therapies, tailoring treatment plans, and monitoring therapy response in real-time.

SubtiToolKit: a bioengineering kit for Bacillus subtilis and Gram-positive bacteria

Building DNA constructs of increasing complexity is key to synthetic biology. Golden Gate (GG) methods led to the creation of cloning toolkits - collections of modular standardized DNA parts hosted on hierarchic plasmids, developed for yeast, plants, Gram-negative bacteria, and human cells. However, Gram-positive bacteria have been neglected. Bacillus subtilis is a Gram-positive model organism and a workhorse in the bioindustry. Here, we present the SubtiToolKit (STK), a high-efficiency cloning toolkit for B. subtilis and Gram-positive bacteria. Its design permits DNA constructs for transcriptional units (TUs), operons, and knockin and knockout applications. The STK contains libraries of promoters, ribosome-binding site (RBSs), fluorescent proteins, protein tags, terminators, genome integration parts, a no-leakage genetic device to control the expression of toxic products during Escherichia coli assembly, and a toolbox for industrially relevant strains of Geobacillus and Parageobacillus as an example of the STK versatility for other Gram-positive bacteria and its future perspective as a reference toolkit.

In Situ Galacto-Oligosaccharides Synthesis in Whey Powder Fortified Milk by a Modified β-Galactosidase and Its Effect on the Techno-Functional Characteristics of Yogurt

In situ galacto-oligosaccharide (GOS) synthesis in milk using β-galactosidases is an effective method for developing prebiotic dairy products. However, the low lactose concentration in milk (∼4.6%, w/w) reduces the GOS yield. In this study, a modified β-galactosidase from Bacillus circulans (mBgaD-D) with enhanced transglycosylation activity at low lactose concentration was developed through directed evolution and saturation mutagenesis. The GOS yield by mBgaD-D increased from 22.8% (wild type) to 30.8% in 50 g/L lactose (phosphate buffer). Pmgut was a strong sorbitol-inducible promoter from Bacillus subtilis. The expression of mBgaD-D in B. subtilis, coupled with the Pmgut promoter, resulted in a 6.4-fold increase (compared to the P43 promoter) in extracellular enzyme activity. Additionally, adding whey powder to boost the initial lactose concentration further improved the GOS yield, which reached 43% under the optimized conditions. Combining mBgaD-D and whey powder enhanced milk sweetness, producing no sugar-added, GOS-enriched yogurt (GOSY). The GOS content in GOSY was 4.1/100 g, providing an appropriate level of sweetness and yielding a yogurt that is elastic as well as firm. GOSY also increased the population of Bifidobacterium spp. during a 24 h in vitro fecal fermentation. Thus, fortifying yogurt with mBgaD-D and whey powder can enhance its technological properties and health benefits.

Heterologous expression and characterization of an unsaturated glucuronyl hydrolase from Alteromonas sp. A321

Strong promoters and stable mRNAs are essential for the overproduction of heterologous proteins in Bacillus subtilis. To improve the strength of natural promoters and ensure robust protein output, promoter and genetic insulator engineering have been used. A series of plasmids containing single and dual promoters and genetic insulators to express alt3796 were engineered, which encoded an unsaturated glucuronyl hydrolase (UGL). As a first step, we screened the host and deleted the signal peptide (SPALT) of alt3796, successfully expressed secreted ALT3796 from B. subtilis WB800. Subsequently, to improve expression, we screened the dual promoter PHag-spoVG from a collection of 22 promoters, which yielded higher enzymatic activity. Finally, using a recombinant strain carrying a plasmid with the PHag-spoVG dual promoter and a genetic insulator, we obtained 40.9 U/mL of activity. Purified recombinant ALT3796 exhibited good stability and specifically degraded ulvan. In conclusion, a system for the heterologous expression of ALT3796 was constructed, and the obtained protein exhibited favorable properties, suggesting its potential for preparing novel ulvan oligosaccharides.

Efficient Production of an Alginate Lyase in Bacillus subtilis with Combined Strategy: Vector and Host Selection, Promoter and Signal Peptide Screening, and Modification of a Translation Initiation Region

Alginate lyases (ALys) whose degrading products, alginate oligosaccharides, exhibit various outstanding biochemical activities have aroused increasing interest of researchers in the marine bioresource field. However, their predominant sourcing from marine bacteria, with limited yields and unclear genetic backgrounds, presents a challenge for industrial production. In this study, ALys (Aly01) from Vibrio natriegens SK 42.001 was expressed in Bacillus subtilis (B. subtilis), a nonpathogenic microorganism recognized as generally safe (GRAS). This accomplishment was realized through a comprehensive strategy involving vector and host selection, promoter and signal peptide screening, and engineering of the ribosome binding site (RBS) and the N-terminal coding sequence (NCS). The optimal combination was identified as the pP43NMK and B. subtilis WB600. Among the 19 reported strong promoters, PnprE exhibited the best performance, showing intracellular enzyme activities of 4.47 U/mL. Despite expectations, dual promoter construction did not yield a significant increase. Further, SPydhT demonstrated the highest extracellular activity (1.33 U/mL), which was further improved by RBS/NCS engineering, reaching 4.58 U/mL. Finally, after fed-batch fermentation, the extracellular activity reached 18.01 U/mL, which was the highest of ALys with a high molecular weight expressed in B. subtilis. These findings are expected to offer valuable insights into the heterologous expression of ALys in B. subtilis.

Bacillus subtilis: current and future modification strategies as a protein secreting factory

Bacillus subtilis is regarded as a promising microbial expression system in bioengineering due to its high stress resistance, nontoxic, low codon preference and grow fast. The strain has a relatively efficient expression system, as it has at least three protein secretion pathways and abundant molecular chaperones, which guarantee its expression ability and compatibility. Currently, many proteins are expressed in Bacillus subtilis, and their application prospects are broad. Although Bacillus subtilis has great advantages compared with other prokaryotes related to protein expression and secretion, it still faces deficiencies, such as low wild-type expression, low product activity, and easy gene loss, which limit its large-scale application. Over the years, many researchers have achieved abundant results in the modification of Bacillus subtilis expression systems, especially the optimization of promoters, expression vectors, signal peptides, transport pathways and molecular chaperones. An optimal vector with a suitable promoter strength and other regulatory elements could increase protein synthesis and secretion, increasing industrial profits. This review highlights the research status of optimization strategies related to the expression system of Bacillus subtilis. Moreover, research progress on its application as a food-grade expression system is also presented, along with some future modification and application directions.

Revisiting microbial exopolysaccharides: a biocompatible and sustainable polymeric material for multifaceted biomedical applications

Microbial exopolysaccharides (EPS) have gained significant attention as versatile biomolecules with multifarious applications across various sectors. This review explores the valorisation of EPS and its potential impact on diverse sectors, including food, pharmaceuticals, cosmetics, and biotechnology. EPS, secreted by microorganisms, possess unique physicochemical properties, such as high molecular weight, water solubility, and biocompatibility, making them attractive for numerous functional roles. Additionally, EPS exhibit significant bioactivity, contributing to their potential use in pharmaceuticals for drug delivery and tissue engineering applications. Moreover, the eco-friendly and sustainable nature of microbial EPS production aligns with the growing demand for environmentally conscious processes. However, challenges still exist in large-scale production, purification, and regulatory approval for commercial use. Advances in bioprocessing and microbial engineering offer promising solutions to overcome these hurdles. Stringent investigations have concluded EPS as novel sources for sustainable applications that are likely to emerge and develop, further reinforcing the significance of these biopolymers in addressing contemporary societal needs and driving innovation in various industrial sectors. Overall, the microbial EPS represents a thriving field with immense potential for meeting diverse industrial demands and advancing sustainable technologies.