Isolation and characterization of violacein from an Antarctic Iodobacter: a non-pathogenic psychrotolerant microorganism

Study on extraction and characterization of new antibiotics violacein from engineered Escherichia coli VioABCDE-SD

To better understand the characteristic properties of violacein biosynthesized by engineered Escherichia coli VioABCDE-SD, a convenient and simplified method was designed to extract violacein and its stability, antimicrobial activity, and antioxidant capacity were analyzed. Different from the traditional extraction methods, our new method is easier and less time consuming and can directly obtain violacein dry powder product with a higher extraction rate. Low temperature, dark condition, neutral pH, reducing agents, Ba2+ , Mn2+ , Ni2+ , Co2+ , and some food additives of sucrose, xylose, and glucose were conducive to maintaining its stability. The violacein also exhibited surprisingly high bacteriostatic action against Gram-positive Bacillus subtilis, Deinococcus radiodurans R1, and Staphylococcus aureus and Gram-negative Pseudomonas aeruginosa, but no effect on E. coli. The violacein of VioABCDE-SD exhibited strong antioxidant activity, with the scavenging rate of 1,1-diphenyl-2-picrylhydrazyl free radicals reaching 60.33%, the scavenging efficiency of hydroxyl radical scavenging reaching 56.34%, and the total antioxidant capacity reaching 0.63 U/mL. Violacein from VioABCDE-SD can be synthesized directionally with better stability, antibacterial, and antioxidant properties compared with that from the original strain Janthinobacterium sp. B9-8. Therefore, our study indicated that violacein from engineered E. coli VioABCDE-SD was a kind of new antibiotic with potential biological activities, which may have potential utility in multiple areas such as pharmacological, cosmetics, and healthy food industries.

Crystal structure of prodigiosin binding protein PgbP, a GNAT family protein, in Serratia marcescens FS14

Acetylation is a conserved modification catalyzed by acetyltransferases that play prominent roles in a large number of biological processes. Members of the general control non-repressible 5 (GCN5)-N-acetyltransferase (GNAT) protein superfamily are widespread in all kingdoms of life and are characterized by highly conserved catalytic fold, and can acetylate a wide range of substrates. Although the structures and functions of numerous eukaryotic GNATs have been identified thus far, many GNATs in microorganisms remain structurally and functionally undescribed. Here, we determined the crystal structure of the putative GCN5-N-acetyltransferase PgbP in complex with CoA in Serratia marcescens FS14. Structural analysis revealed that the PgbP dimer has two cavities, each of which binds a CoA molecule via conserved motifs of the GNAT family. In addition, the biochemical studies showed that PgbP is a prodigiosin-binding protein with high thermal stability. To our knowledge, this is the first view of GNAT binding to secondary metabolites and it is also the first report of prodigiosin binding protein. Molecular docking and mutation experiments indicated that prodigiosin binds to the substrate binding site of PgbP. The structure-function analyses presented here broaden our understanding of the multifunctionality of GNAT family members and may infer the mechanism of the multiple biological activities of prodigiosin.

Multiple Adaptive Strategies of Himalayan Iodobacter sp. PCH194 to High-Altitude Stresses

Bacterial adaption to the multiple stressed environments of high-altitude niches in the Himalayas is intriguing and is of considerable interest to biotechnologists. Previously, we studied the culturable and unculturable metagenome microbial diversity from glacial and kettle lakes in the Western Himalayas. In this study, we explored the adaptive strategies of a unique Himalayan eurypsychrophile Iodobacter sp. PCH194, which can synthesize polyhydroxybutyrate (PHB) and violacein pigment. Whole-genome sequencing and analysis of Iodobacter sp. PCH194 (4.58 Mb chromosome and three plasmids) revealed genetic traits associated with adaptive strategies for cold/freeze, nutritional fluctuation, defense against UV, acidic pH, and the kettle lake's competitive environment. Differential proteome analysis suggested the adaptive role of chaperones, ribonucleases, secretion systems, and antifreeze proteins under cold stress. Antifreeze activity inhibiting the ice recrystallization at −9°C demonstrated the bacterium's survival at subzero temperature. The bacterium stores carbon in the form of PHB under stress conditions responding to nutritional fluctuations. However, violacein pigment protects the cells from UV radiation. Concisely, genomic, proteomic, and physiological studies revealed the multiple adaptive strategies of Himalayan Iodobacter to survive the high-altitude stresses.

Next-Generation Genetic and Fermentation Technologies for Safe and Sustainable Production of Food Ingredients: Colors and Flavorings

A growing human population is a significant issue in food security owing to the limited land and resources available for agricultural food production. To solve these problems, sustainable food manufacturing processes and the development of alternative foods and ingredients are needed. Metabolic engineering and synthetic biology can help solve the food security issue and satisfy the demand for alternative food production. Bioproduction of food ingredients by microbial fermentation is a promising method to replace current manufacturing processes, such as extraction from natural materials and chemical synthesis, with more ecofriendly and sustainable operations. This review highlights successful examples of bioproduction for food additives by engineered microorganisms, with an emphasis on colorants and flavors that are extensively used in the food industry. Recent strain engineering developments and fermentation strategies for producing selected food colorants and flavors are introduced with discussions on the current status and future perspectives.

Expected final online publication date for the Annual Review of Food Science and Technology, Volume 13 is March 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

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.

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.

Microbial synthesis of violacein pigment and its potential applications

Violacein is a pigment synthesized by Gram-negative bacteria such as Chromobacterium violaceum. It has garnered significant interest owing to its unique physiological and biological activities along with its synergistic effects with various antibiotics. In addition to C. violaceum, several microorganisms, including: Duganella sp., Pseudoalteromonas sp., Iodobacter sp., and Massilia sp., are known to produce violacein. Along with the identification of violacein-producing strains, the genetic regulation, quorum sensing mechanism, and sequence of the vio-operon involved in the biosynthesis of violacein have been elucidated. From an engineering perspective, the heterologous production of violacein using the genetically engineered Escherichia coli or Citrobacter freundii host has also been attempted. Genetic engineering of host cells involves the heterologous expression of genes involved in the vio operon and the optimization of metabolic pathways and gene regulation. Further, the crystallography of VioD and VioE was revealed, and mass production by enzyme engineering has been accelerated. In this review, we highlight the biologically assisted end-use applications of violacein (such as functional fabric development, nanoparticles, functional polymer composites, and sunscreen ingredients) and violacein activation mechanisms, production strains, and the results of mass production with engineered methods. The prospects for violacein research and engineering applications have also been discussed.

Pigments from Antarctic bacteria and their biotechnological applications

Pigments from microorganisms have triggered great interest in the market, mostly by their "natural" appeal, their favorable production conditions, in addition to the potential new chemical structures or naturally overproducing strains. They have been used in: food, feed, dairy, textile, pharmaceutical, and cosmetic industries. The high rate of pigment production in microorganisms recovered from Antarctica in response to selective pressures such as: high UV radiation, low temperatures, and freezing and thawing cycles makes this a unique biome which means that much of its biological heritage cannot be found elsewhere on the planet. This vast arsenal of pigmented molecules has different functions in bacteria and may exhibit different biotechnological activities, such as: extracellular sunscreens, photoprotective function, antimicrobial activity, biodegradability, etc. However, many challenges for the commercial use of these compounds have yet to be overcome, such as: the low stability of natural pigments in cosmetic formulations, the change in color when subjected to pH variations, the low yield and the high costs in their production. This review surveys the different types of natural pigments found in Antarctic bacteria, classifying them according to their chemical structure. Finally, we give an overview of the main pigments that are used commercially today.

Bioprocess for co-production of polyhydroxybutyrate and violacein using Himalayan bacterium Iodobacter sp. PCH194

The co-production of industrially relevant biopolymers/biomolecules from microbes is of biotechnological importance. Herein, a unique bacterium, Iodobacter sp. PCH 194 from the kettle lake at Sach Pass in western Indian Himalaya was identified. It co-produces biopolymer polyhydroxyalkanoates (PHA) and biomolecule (violacein pigment). Statistical optimization yielded dual products in the medium augmented with glucose (4.0% w/v) and tryptone (0.5% w/v) as carbon and nitrogen sources, respectively. The purified PHA was polyhydroxybutyrate (PHB), and pigment constitutes of violacein (50-60%) and deoxyviolacein (40-50%). A bench-scale bioprocess in 22.0 L fermentor with 20% dissolved O₂ supply produced PHB (11.0 ± 1.0 g/L, 58% of dry cell mass) and violacein pigment (1.5 ± 0.08 g/L). PHB obtained was used for the preparation of bioplastic film. Violacein pigment experimentally validated for anticancerous and antimicrobial activities. In summary, a commercially implied bioprocess developed for the co-production of PHB and violacein pigment using the Himalayan bacterium.

An Overview on Industrial and Medical Applications of Bio-Pigments Synthesized by Marine Bacteria

Marine bacterial species contribute to a significant part of the oceanic population, which substantially produces biologically effectual moieties having various medical and industrial applications. The use of marine-derived bacterial pigments displays a snowballing effect in recent times, being natural, environmentally safe, and health beneficial compounds. Although isolating marine bacteria is a strenuous task, these are still a compelling subject for researchers, due to their promising avenues for numerous applications. Marine-derived bacterial pigments serve as valuable products in the food, pharmaceutical, textile, and cosmetic industries due to their beneficial attributes, including anticancer, antimicrobial, antioxidant, and cytotoxic activities. Biodegradability and higher environmental compatibility further strengthen the use of marine bio-pigments over artificially acquired colored molecules. Besides that, hazardous effects associated with the consumption of synthetic colors further substantiated the use of marine dyes as color additives in industries as well. This review sheds light on marine bacterial sources of pigmented compounds along with their industrial applicability and therapeutic insights based on the data available in the literature. It also encompasses the need for introducing bacterial bio-pigments in global pigment industry, highlighting their future potential, aiming to contribute to the worldwide economy.