Integrated bioprocess for the stereospecific production of linalool oxides from linalool with Corynespora cassiicola DSM 62475

Natural Compounds in the Battle against Microorganisms-Linalool

The purpose of this article is to present recent studies on the antimicrobial properties of linalool, the mechanism of action on cells and detoxification processes. The current trend of employing compounds present in essential oils to support antibiotic therapy is becoming increasingly popular. Naturally occurring monoterpene constituents of essential oils are undergoing detailed studies to understand their detailed effects on the human body, both independently and in doses correlated with currently used pharmaceuticals. One such compound is linalool, which is commonly found in many herbs and is used to flavor black tea. This compound is an excellent fragrance additive for cosmetics, enhancing the preservative effect of the formulations used in them or acting as an anti-inflammatory on mild skin lesions. Previous studies have shown that it is extremely important due to its broad spectrum of biological activities, i.e., antioxidant, anti-inflammatory, anticancer, cardioprotective and antimicrobial. Among opportunistic hospital strains, it is most active against Gram-negative bacteria. The mechanism of action of linalool against microorganisms is still under intensive investigation. One of the key aspects of linalool research is biotransformation, through which its susceptibility to detoxification processes is determined.

An update on the progress of microbial biotransformation of commercial monoterpenes

Monoterpenes, a class of isoprenoid compounds, are extensively used in flavor, fragrance, perfumery, and cosmetics. They display many astonishing bioactive properties of biological and pharmacological significance. All monoterpenes are derived from universal precursor geranyl diphosphate. The demand for new monoterpenoids has been increasing in flavor, fragrances, perfumery, and pharmaceuticals. Chemical methods, which are harmful for human and the environment, synthesize most of these products. Over the years, researchers have developed alternative methods for the production of newer monoterpenoids. Microbial biotransformation is one of them, which relied on microbes and their enzymes. It has produced many new desirable commercially important monoterpenoids. A growing number of reports reflect an ever-expanding scope of microbial biotransformation in food and aroma industries. Simultaneously, our knowledge of the enzymology of monoterpene biosynthetic pathways has been increasing, which facilitated the biotransformation of monoterpenes. In this article, we have covered the progress made on microbial biotransformation of commercial monoterpenes with a brief introduction to their biosynthesis. We have collected several reports from authentic web sources, including Google Scholar, Pubmed, Web of Science, and Scopus published in the past few years to extract information on the topic.

Metabolic engineering and synthetic biology for isoprenoid production in Escherichia coli and Saccharomyces cerevisiae

Isoprenoids, often called terpenoids, are the most abundant and highly diverse family of natural organic compounds. In plants, they play a distinct role in the form of photosynthetic pigments, hormones, electron carrier, structural components of membrane, and defence. Many isoprenoids have useful applications in the pharmaceutical, nutraceutical, and chemical industries. They are synthesized by various isoprenoid synthase enzymes by several consecutive steps. Recent advancement in metabolic engineering and synthetic biology has enabled the production of these isoprenoids in the heterologous host systems like Escherichia coli and Saccharomyces cerevisiae. Both heterologous systems have been engineered for large-scale production of value-added isoprenoids. This review article will provide the detailed description of various approaches used for engineering of methyl-D-erythritol-4-phosphate (MEP) and mevalonate (MVA) pathway for synthesizing isoprene units (C₅) and ultimate production of diverse isoprenoids. The review particularly highlighted the efforts taken for the production of C₅-C₂₀ isoprenoids by metabolic engineering techniques in E. coli and S. cerevisiae over a decade. The challenges and strategies are also discussed in detail for scale-up and engineering of isoprenoids in the heterologous host systems.Key points• Isoprenoids are beneficial and valuable natural products.• E. coli and S. cerevisiae are the promising host for isoprenoid biosynthesis.• Emerging techniques in synthetic biology enabled the improved production.• Need to expand the catalogue and scale-up of un-engineered isoprenoids. Metabolic engineering and synthetic biology for isoprenoid production in Escherichia coli and Saccharomyces cerevisiae.

Whole-Cell Production of Patchouli Oil Sesquiterpenes in Escherichia coli: Metabolic Engineering and Fermentation Optimization in Solid-Liquid Phase Partitioning Cultivation

Patchouli oil is a major ingredient in perfumery, granting a dark-woody scent due to its main constituent (-)-patchoulol. The growing demand for patchouli oil has raised interest in the development of a biotechnological process to assure a reliable supply. Herein, we report the production of patchouli oil sesquiterpenes by metabolically engineered Escherichia coli strains, using solid-liquid phase partitioning cultivation. The (-)-patchoulol production was possible using the endogenous methylerythritol phosphate pathway and overexpressing a (-)-patchoulol synthase isoform from Pogostemon cablin but at low titers. To improve the (-)-patchoulol production, the exogenous mevalonate pathway was overexpressed in the multi-plasmid PTS + Mev strain, which increased the (-)-patchoulol titer 5-fold. Fermentation was improved further by evaluating several defined media, and optimizing the pH and temperature of culture broth, enhancing the (-)-patchoulol titer 3-fold. To augment the (-)-patchoulol recovery from fermentation, the solid-liquid phase partitioning cultivation was analyzed by screening polymeric adsorbers, where the Diaion HP20 adsorber demonstrated the highest (-)-patchoulol recovery from all tests. Fermentation was scaled-up to fed-batch bioreactors, reaching a (-)-patchoulol titer of 40.2 mg L-1 and productivity of 20.1 mg L-1 d-1. The terpene profile and aroma produced from the PTS + Mev strain were similar to the patchouli oil, comprising (-)-patchoulol as the main product, and α-bulnesene, trans-β-caryophyllene, β-patchoulene, and guaia-5,11-diene as side products. This investigation represents the first study of (-)-patchoulol production in E. coli by solid-liquid phase partitioning cultivation, which provides new insights for the development of sustainable bioprocesses for the microbial production of fragrant terpenes.

Improved Production and In Situ Recovery of Sesquiterpene (+)-Zizaene from Metabolically-Engineered E. coli

The sesquiterpene (+)-zizaene is the direct precursor of khusimol, the main fragrant compound of the vetiver essential oil from Chrysopogon zizanioides and used in nearly 20% of men's fine perfumery. The biotechnological production of such fragrant sesquiterpenes is a promising alternative towards sustainability; nevertheless, product recovery from fermentation is one of the main constraints. In an effort to improve the (+)-zizaene recovery from a metabolically-engineered Escherichia coli, we developed an integrated bioprocess by coupling fermentation and (+)-zizaene recovery using adsorber extractants. Initially, (+)-zizaene volatilization was confirmed from cultivations with no extractants but application of liquid-liquid phase partitioning cultivation (LLPPC) improved (+)-zizaene recovery nearly 4-fold. Furthermore, solid-liquid phase partitioning cultivation (SLPPC) was evaluated by screening polymeric adsorbers, where Diaion HP20 reached the highest recovery. Bioprocess was scaled up to 2 L bioreactors and in situ recovery configurations integrated to fermentation were evaluated. External recovery configuration was performed with an expanded bed adsorption column and improved (+)-zizaene titers 2.5-fold higher than LLPPC. Moreover, internal recovery configuration (IRC) further enhanced the (+)-zizaene titers 2.2-fold, whereas adsorption velocity was determined as critical parameter for recovery efficiency. Consequently, IRC improved the (+)-zizaene titer 8.4-fold and productivity 3-fold from our last report, achieving a (+)-zizaene titer of 211.13 mg L-1 and productivity of 3.2 mg L-1 h-1. This study provides further knowledge for integration of terpene bioprocesses by in situ product recovery, which could be applied for many terpene studies towards the industrialization of fragrant molecules.

Efficient hydroxylation of 1,8-cineole with monoterpenoid-resistant recombinant Pseudomonas putida GS1

In this work, monoterpenoid hydroxylation with Pseudomonas putida GS1 and KT2440 were investigated as host strains, and the cytochrome P450 monooxygenase CYP176A1 (P450cin) and its native redox partner cindoxin (CinC) from Citrobacter braakii were introduced in P. putida to catalyze the stereoselective hydroxylation of 1,8-cineole to (1R)-6β-hydroxy-1,8-cineole. Growth experiments in the presence of 1,8-cineole confirmed pseudomonads' superior resilience compared to E. coli. Whole-cell P. putida harboring P450cin with and without CinC were capable of hydroxylating 1,8-cineole, whereas coexpression of CinC has been shown to accelerate this bioconversion. Under the same conditions, P. putida GS1 produced more than twice the amount of heterologous P450cin and bioconversion product than P. putida KT2440. A concentration of 1.1 ± 0.1 g/L (1R)-6β-hydroxy-1,8-cineole was obtained within 55 h in shake flasks and 13.3 ± 1.9 g/L in 89 h in a bioreactor, the latter of which corresponds to a yield YP/S of 79 %. To the authors' knowledge, this is the highest product titer for a P450 based whole-cell monoterpene oxyfunctionalization reported so far. These results show that solvent-tolerant P. putida GS1 can be used as a highly efficient recombinant whole-cell biocatalyst for a P450 monooxygenase-based valorization of monoterpenoids.

Bioprocess engineering for microbial synthesis and conversion of isoprenoids

Isoprenoids represent a natural product class essential to living organisms. Moreover, industrially relevant isoprenoid molecules cover a wide range of products such as pharmaceuticals, flavors and fragrances, or even biofuels. Their often complex structure makes chemical synthesis a difficult and expensive task and extraction from natural sources is typically low yielding. This has led to intense research for biotechnological production of isoprenoids by microbial de novo synthesis or biotransformation. Here, metabolic engineering, including synthetic biology approaches, is the key technology to develop efficient production strains in the first place. Bioprocess engineering, particularly in situ product removal (ISPR), is the second essential technology for the development of industrial-scale bioprocesses. A number of elaborate bioreactor and ISPR designs have been published to target the problems of isoprenoid synthesis and conversion, such as toxicity and product inhibition. However, despite the many exciting applications of isoprenoids, research on isoprenoid-specific bioprocesses has mostly been, and still is, limited to small-scale proof-of-concept approaches. This review presents and categorizes different ISPR solutions for biotechnological isoprenoid production and also addresses the main challenges en route towards industrial application.