Optimization of industrial microorganisms: recent advances in synthetic dynamic regulators

Whole-genome analysis suggesting probiotic potential and safety properties of Pediococcus pentosaceus DSPZPP1, a promising LAB strain isolated from traditional fermented sausages of the Basilicata region (Southern Italy)

Introduction

Many lactic acid bacteria (LAB) strains are currently gaining attention in the food industry and various biological applications because of their harmless and functional properties. Given the growing consumer demand for safe food, further research into potential probiotic bacteria is beneficial. Therefore, we aimed to characterize Pediococcus pentosaceus DSPZPP1, a LAB strain isolated from traditional fermented sausages from the Basilicata region of Southern Italy.

Methods

In this study, we analyzed the whole genome of the P. pentosaceus DSPZPP1 strain and performed in silico characterization to evaluate its applicability for probiotics and use in the food industry.

Results and Discussion

The whole-genome assembly and functional annotations revealed many interesting characteristics of the DSPZPP1 strain. Sequencing raw reads were assembled into a draft genome of size 1,891,398 bp, with a G + C content of 37.3%. Functional annotation identified 1930 protein-encoding genes and 58 RNAs including tRNA, tmRNA, and 16S, 23S, and 5S rRNAs. The analysis shows the presence of genes that encode water-soluble B-group vitamins such as biotin, folate, coenzyme A, and riboflavin. Furthermore, the analysis revealed that the DSPZPP1 strain can synthesize class II bacteriocin, penocin A, adding importance to the food industry for bio-enriched food. The DSPZPP1 genome does not show the presence of plasmids, and no genes associated with antimicrobial resistance and virulence were found. In addition, two intact bacteriophages were identified. Importantly, the lowest probability value in pathogenicity analysis indicates that this strain is non-pathogenic to humans. 16 s rRNA-based phylogenetic analysis and comparative analysis based on ANI and Tetra reveal that the DSPZPP1 strain shares the closest evolutionary relationship with P. pentosaceus DSM 20336 and other Pediococcus strains. Analysis of carbohydrate active enzymes (CAZymes) identified glycosyl transferases (GT) as a main class of enzymes followed by glycoside hydrolases (GH). Our study shows several interesting characteristics of the isolated DSPZPP1 strain from fermented Italian sausages, suggesting its potential use as a promising probiotic candidate and making it more appropriate for selection as a future additive in biopreservation.

MoBioS: Modular Platform Technology for High-Throughput Construction and Characterization of Tunable Transcriptional Biological Sensors

All living organisms have evolved and fine-tuned specialized mechanisms to precisely monitor a vast array of different types of molecules. These natural mechanisms can be sourced by researchers to build Biological Sensors (BioS) by combining them with an easily measurable output, such as fluorescence. Because they are genetically encoded, BioS are cheap, fast, sustainable, portable, self-generating and highly sensitive and specific. Therefore, BioS hold the potential to become key enabling tools that stimulate innovation and scientific exploration in various disciplines. However, the main bottleneck in unlocking the full potential of BioS is the fact that there is no standardized, efficient and tunable platform available for the high-throughput construction and characterization of biosensors. Therefore, a modular, Golden Gate-based construction platform, called MoBioS, is introduced in this article. It allows for the fast and easy creation of transcription factor-based biosensor plasmids. As a proof of concept, its potential is demonstrated by creating eight different, functional and standardized biosensors that detect eight diverse molecules of industrial interest. In addition, the platform contains novel built-in features to facilitate fast and efficient biosensor engineering and response curve tuning.

Dynamic flux regulation for high-titer anthranilate production by plasmid-free, conditionally-auxotrophic strains of Pseudomonas putida

Anthranilate, an intermediate of the shikimate pathway, is a high-value aromatic compound widely used as a precursor in the production of dyes, fragrances, plastics and pharmaceuticals. Traditional strategies adopted for microbial anthranilate production rely on the implementation of auxotrophic strains-which requires aromatic amino acids or complex additives to be supplemented in the culture medium, negatively impacting production costs. In this work, we engineered the soil bacterium Pseudomonas putida for high-titer, glucose-dependent anthranilate production by repurposing elements of the Esa quorum sensing (QS) system of Pantoea stewartii. The P_esaS promoter mediated a self-regulated transcriptional response that effectively knocked-down the expression of the trpDC genes. Next, we harnessed the synthetic QS elements to engineer a growth-to-anthranilate production switch. The resulting plasmid-free P. putida strain produced the target compound at 3.8 ± 0.3 mM in shaken-flask cultures after 72 h-a titer >2-fold higher than anthranilate levels reported thus far. Our results highlight the value of dynamic flux regulation for the production of intermediate metabolites within highly-regulated routes (such as the shikimate pathway), thereby circumventing the need of expensive additives.

Pediococcus pentosaceus, a future additive or probiotic candidate

Background

Pediococcus pentosaceus, a promising strain of lactic acid bacteria (LAB), is gradually attracting attention, leading to a rapid increase in experimental research. Due to increased demand for practical applications of microbes, the functional and harmless P. pentosaceus might be a worthwhile LAB strain for both the food industry and biological applications.

Results

As an additive, P. pentosaceus improves the taste and nutrition of food, as well as the storage of animal products. Moreover, the antimicrobial abilities of Pediococcus strains are being highlighted. Evidence suggests that bacteriocins or bacteriocin-like substances (BLISs) produced by P. pentosaceus play effective antibacterial roles in the microbial ecosystem. In addition, various strains of P. pentosaceus have been highlighted for probiotic use due to their anti-inflammation, anticancer, antioxidant, detoxification, and lipid-lowering abilities.

Conclusions

Therefore, it is necessary to continue studying P. pentosaceus for further use. Thorough study of several P. pentosaceus strains should clarify the benefits and drawbacks in the future.

Automated engineering of synthetic metabolic pathways for efficient biomanufacturing

Metabolic engineering involves the engineering and optimization of processes from single-cell to fermentation in order to increase production of valuable chemicals for health, food, energy, materials and others. A systems approach to metabolic engineering has gained traction in recent years thanks to advances in strain engineering, leading to an accelerated scaling from rapid prototyping to industrial production. Metabolic engineering is nowadays on track towards a truly manufacturing technology, with reduced times from conception to production enabled by automated protocols for DNA assembly of metabolic pathways in engineered producer strains. In this review, we discuss how the success of the metabolic engineering pipeline often relies on retrobiosynthetic protocols able to identify promising production routes and dynamic regulation strategies through automated biodesign algorithms, which are subsequently assembled as embedded integrated genetic circuits in the host strain. Those approaches are orchestrated by an experimental design strategy that provides optimal scheduling planning of the DNA assembly, rapid prototyping and, ultimately, brings forward an accelerated Design-Build-Test-Learn cycle and the overall optimization of the biomanufacturing process. Achieving such a vision will address the increasingly compelling demand in our society for delivering valuable biomolecules in an affordable, inclusive and sustainable bioeconomy.

Molecular parts and genetic circuits for metabolic engineering of microorganisms

Microbial conversion of biomass into value-added biochemicals is a highly sustainable process compared to petroleum-based production. In this regard, microorganisms have been engineered via simple overexpression or deletion of metabolic genes to facilitate the production. However, the producer microorganisms require complex regulatory circuits to maximize productivity and performance. To address this issue, diverse genetic circuits have been developed that allow cells to minimize their metabolic burden, overcome metabolic imbalances and respond to a dynamically changing environment. In this review, we briefly explain the basic strategy for constructing genetic circuits by assembling molecular parts such as input, operation and output modules. Next, we describe recent applications of the circuits in the metabolic engineering of microorganisms to improve biochemical production. Beyond those achievements, genetic circuits will facilitate more innovative approaches to future strain development through mining and engineering new genetic elements and improving the complexity of genetic circuit design.

Enterobacter oligotrophica sp. nov., a novel oligotroph isolated from leaf soil

A novel oligotrophic bacterium, designated strain CCA6, was isolated from leaf soil collected in Japan. Cells of the strain were found to be a Gram‐negative, non‐sporulating, motile, rod‐shaped bacterium. Strain CCA6 grew at 10–45°C (optimum 20°C) and pH 4.5–10.0 (optimum pH 5.0). The strain was capable of growth in poor‐nutrient (oligotrophic) medium, and growth was unaffected by high‐nutrient medium. The major fatty acid and predominant quinone system were C_16:0 and ubiquinone‐8. Phylogenetic analysis based on 16S rRNA gene sequences indicated strain CCA6 presented as a member of the family Enterobacteriaceae. Multilocus sequence analysis (MLSA) based on fragments of the atpD, gyrB, infB, and rpoB gene sequences was performed to further identify strain CCA6. The MLSA showed clear branching of strain CCA6 with respect to Enterobacter type strains. The complete genome of strain CCA6 consisted of 4,476,585 bp with a G+C content of 54.3% and comprising 4,372 predicted coding sequences. The genome average nucleotide identity values between strain CCA6 and the closest related Enterobacter type strain were <88.02%. Based on its phenotypic, chemotaxonomic and phylogenetic features, strain CCA6 (=HUT 8142^T =KCTC 62525^T) can be considered as a novel species within the genus Enterobacter with the proposed name Enterobacter oligotrophica.

Dynamic control of endogenous metabolism with combinatorial logic circuits

Controlling gene expression during a bioprocess enables real-time metabolic control, coordinated cellular responses, and staging order-of-operations. Achieving this with small molecule inducers is impractical at scale and dynamic circuits are difficult to design. Here, we show that the same set of sensors can be integrated by different combinatorial logic circuits to vary when genes are turned on and off during growth. Three Escherichia coli sensors that respond to the consumption of feedstock (glucose), dissolved oxygen, and by-product accumulation (acetate) are constructed and optimized. By integrating these sensors, logic circuits implement temporal control over an 18-h period. The circuit outputs are used to regulate endogenous enzymes at the transcriptional and post-translational level using CRISPRi and targeted proteolysis, respectively. As a demonstration, two circuits are designed to control acetate production by matching their dynamics to when endogenous genes are expressed (pta or poxB) and respond by turning off the corresponding gene. This work demonstrates how simple circuits can be implemented to enable customizable dynamic gene regulation.

Separation and purification of α-ketoglutarate and pyruvate from the fermentation broth of Yarrowia lipolytica

A strategy to achieve the efficient co-production of α-ketoglutarate (KGA) and pyruvate (PYR) via Yarrowia lipolytica fermentation was established in our previous work. The next big challenge is to achieve an efficient separation of the two keto acids. A strategy for simultaneously separating and purifying KGA and PYR based on their different boiling points was established, leading to the efficient separation and purification of the two keto acids from the fermentation broth of Y. lipolytica. The purity and yield of KGA/PYR reached 99.3/99.5 and 79.8/80.6%, respectively. Application of the separation method on industrial scale could further decrease the cost of the production of the two keto acids by biotechnological routes.

Synthetic auxotrophs for stable and tunable maintenance of plasmid copy number

Although plasmid-based expression systems have advantages in multi-copy expression of genes, heterogeneity of plasmid copy number (PCN) in individual cells is inevitable even with the addition of antibiotics. Here, we developed a synthetic auxotrophic system for stable and tunable maintenance of the PCN in Escherichia coli without addition of antibiotics. This auxotroph expresses infA, one of the essential genes encoding a translation initiation factor, on a plasmid instead of on the chromosome. With this system, the gene expression was stably maintained for 40 generations with minimized cell-to-cell variation under antibiotic-free conditions. Moreover, varying the expression level of infA enabled us to rationally tune the PCN by more than 5.6-fold. This antibiotic-free PCN control system significantly improved the production of itaconic acid and lycopene compared to the conventional system based on antibiotics (2-fold). Collectively, the developed strategy could be a platform for the production of value-added products in antibiotic-free cultivation.