Coupling Yeast Golden Gate and VEGAS for Efficient Assembly of the Violacein Pathway in Saccharomyces cerevisiae

High-Titer Production of the Fungal Anhydrotetracycline, TAN-1612, in Engineered Yeasts

Antibiotic resistance is a growing global health threat, demanding urgent responses. Tetracyclines, a widely used antibiotic class, are increasingly succumbing to antibiotic resistance; generating novel analogues is therefore a top priority for public health. Fungal tetracyclines provide structural and enzymatic diversity for novel tetracycline analogue production in tractable heterologous hosts, like yeasts, to combat antibiotic-resistant pathogens. Here, we successfully engineered Saccharomyces cerevisiae (baker's yeast) and Saccharomyces boulardii (probiotic yeast) to produce the nonantibiotic fungal anhydrotetracycline, TAN-1612, in synthetic defined media─necessary for clean purifications─through heterologously expressing TAN-1612 genes mined from the fungus, Aspergillus niger ATCC 1015. This was accomplished via (i) a promoter library-based combinatorial pathway optimization of the biosynthetic TAN-1612 genes coexpressed with a putative TAN-1612 efflux pump, reducing TAN-1612 toxicity in yeasts while simultaneously increasing supernatant titers and (ii) the development of a medium-throughput UV-visible spectrophotometric assay that facilitates TAN-1612 combinatorial library screening. Through this multipronged approach, we optimized TAN-1612 production, yielding an over 450-fold increase compared to previously reported S. cerevisiae yields. TAN-1612 is an important tetracycline analogue precursor, and we thus present the first step toward generating novel tetracycline analogue therapeutics to combat current and emerging antibiotic resistance. We also report the first heterologous production of a fungal polyketide, like TAN-1612, in the probiotic S. boulardii. This highlights that engineered S. boulardii can biosynthesize complex natural products like tetracyclines, setting the stage to equip probiotic yeasts with synthetic therapeutic functionalities to generate living therapeutics or biocontrol agents for clinical and agricultural applications.

Recent Advances in Synthetic, Industrial and Biological Applications of Violacein and Its Heterologous Production

Violacein, a purple pigment first isolated from a gram-negative coccobacillus Chromobacterium violaceum, has gained extensive research interest in recent years due to its huge potential in the pharmaceutic area and industry. In this review, we summarize the latest research advances concerning this pigment, which include (1) fundamental studies of its biosynthetic pathway, (2) production of violacein by native producers, apart from C. violaceum, (3) metabolic engineering for improved production in heterologous hosts such as Escherichia coli, Citrobacter freundii, Corynebacterium glutamicum, and Yarrowia lipolytica, (4) biological/pharmaceutical and industrial properties, (5) and applications in synthetic biology. Due to the intrinsic properties of violacein and the intermediates during its biosynthesis, the prospective research has huge potential to move this pigment into real clinical and industrial applications.

Yeast synthetic biology advances biofuel production

Increasing concerns of environmental impacts and global warming calls for urgent need to switch from use of fossil fuels to renewable technologies. Biofuels represent attractive alternatives of fossil fuels and have gained continuous attentions. Through the use of synthetic biology it has become possible to engineer microbial cell factories for efficient biofuel production in a more precise and efficient manner. Here, we review advances on yeast-based biofuel production. Following an overview of synthetic biology impacts on biofuel production, we review recent advancements on the design, build, test, learn steps of yeast-based biofuel production, and end with discussion of challenges associated with use of synthetic biology for developing novel processes for biofuel production.

Multi-target drug with potential applications: violacein in the spotlight

The aim of the current review is to address updated research on a natural pigment called violacein, with emphasis on its production, biological activity and applications. New information about violacein's action mechanisms as antitumor agent and about its synergistic action in drug delivery systems has brought new alternatives for anticancer therapy. Thus, violacein is introduced as reliable drug capable of overcoming at least three cancer hallmarks, namely: proliferative signaling, cell death resistance and metastasis. In addition, antimicrobial effects on several microorganisms affecting humans and other animals turn violacein into an attractive drug to combat resistant pathogens. Emphasis is given to effects of violacein combined with different agents, such as antibiotics, anticancer agents and nanoparticles. Although violacein is well-known for many decades, it remains an attractive compound. Thus, research groups have been making continuous effort to help improving its production in recent years, which can surely enable its pharmaceutical and chemical application as multi-task compound, even in the cosmetics and food industries.

Biotechnological Activities and Applications of Bacterial Pigments Violacein and Prodigiosin

In this review, we discuss violacein and prodigiosin, two chromogenic bacterial secondary metabolites that have diverse biological activities. Although both compounds were "discovered" more than seven decades ago, interest into their biological applications has grown in the last two decades, particularly driven by their antimicrobial and anticancer properties. These topics will be discussed in the first half of this review. The latter half delves into the current efforts of groups to produce these two compounds. This includes in both their native bacterial hosts and heterogeneously in other bacterial hosts, including discussing some of the caveats related to the yields reported in the literature, and some of the synthetic biology techniques employed in this pursuit.

Combinatorial metabolic pathway assembly approaches and toolkits for modular assembly

Synthetic Biology is a rapidly growing interdisciplinary field that is primarily built upon foundational advances in molecular biology combined with engineering design principles such as modularity and interoperability. The field considers living systems as programmable at the genetic level and has been defined by the development of new platform technologies and methodological advances. A key concept driving the field is the Design-Build-Test-Learn cycle which provides a systematic framework for building new biological systems. One major application area for synthetic biology is biosynthetic pathway engineering that requires the modular assembly of different genetic regulatory elements and biosynthetic enzymes. In this review we provide an overview of modular DNA assembly and describe and compare the plethora of in vitro and in vivo assembly methods for combinatorial pathway engineering. Considerations for part design and methods for enzyme balancing are also presented, and we briefly discuss alternatives to intracellular pathway assembly including microbial consortia and cell-free systems for biosynthesis. Finally, we describe computational tools and automation for pathway design and assembly and argue that a deeper understanding of the many different variables of genetic design, pathway regulation and cellular metabolism will allow more predictive pathway design and engineering.

Antiplasmodial and trypanocidal activity of violacein and deoxyviolacein produced from synthetic operons

BACKGROUND

Violacein is a deep violet compound that is produced by a number of bacterial species. It is synthesized from tryptophan by a pathway that involves the sequential action of 5 different enzymes (encoded by genes vioA to vioE). Violacein has antibacterial, antiparasitic, and antiviral activities, and also has the potential of inducing apoptosis in certain cancer cells.

RESULTS

Here, we describe the construction of a series of plasmids harboring the complete or partial violacein biosynthesis operon and their use to enable production of violacein and deoxyviolacein in E.coli. We performed in vitro assays to determine the biological activity of these compounds against Plasmodium, Trypanosoma, and mammalian cells. We found that, while deoxyviolacein has a lower activity against parasites than violacein, its toxicity to mammalian cells is insignificant compared to that of violacein.

CONCLUSIONS

We constructed E. coli strains capable of producing biologically active violacein and related compounds, and propose that deoxyviolacein might be a useful starting compound for the development of antiparasite drugs.