Gopal Prasad Ghimire

Improved Squalene Production via Modulation of the Methylerythritol 4-Phosphate Pathway and Heterologous Expression of Genes from Streptomyces peucetius ATCC 27952 in Escherichia coli

ABSTRACT Putative hopanoid genes from Streptomyces peucetius were introduced into Escherichia coli to improve the production of squalene, an industrially important compound. High expression of hopA and hopB (encoding squalene/phytoene synthases) together with hopD (encoding farnesyl diphosphate synthase) yielded 4.1 mg/liter of squalene. This level was elevated to 11.8 mg/liter when there was also increased expression of dxs and idi, E. coli genes encoding 1-deoxy-d-xylulose 5-phosphate synthase and isopentenyl diphosphate isomerase.

Advances in Biochemistry and Microbial Production of Squalene and Its Derivatives.

Squalene is a linear triterpene formed via the MVA or MEP biosynthetic pathway and is widely distributed in bacteria, fungi, algae, plants, and animals. Metabolically, squalene is used not only as a precursor in the synthesis of complex secondary metabolites such as sterols, hormones, and vitamins, but also as a carbon source in aerobic and anaerobic fermentation in microorganisms. Owing to the increasing roles of squalene as an antioxidant, anticancer, and anti-inflammatory agent, the demand for this chemical is highly urgent. As a result, with the exception of traditional methods of the isolation of squalene from animals (shark liver oil) and plants, biotechnological methods using microorganisms as producers have afforded increased yield and productivity, but a reduction in progress. In this paper, we first review the biosynthetic routes of squalene and its typical derivatives, particularly the squalene synthase route. Second, typical biotechnological methods for the enhanced production of squalene using microbial cell factories are summarized and classified. Finally, the outline and discussion of the novel trend in the production of squalene with several updated events to 2015 are presented.

Enzymatic glycosylation of the topical antibiotic mupirocin

Mupirocin is a commercially available antibiotic that acts on bacterial isoleucyl-tRNA synthetase, thereby inhibiting protein synthesis and preventing bacterial infection. An in vitro glycosylation approach was applied to synthesize glycoside derivatives of mupirocin using different NDP-sugars and glycosyltransferase from Bacillus licheniformis. Ultra pressure liquid chromatography-photo diode array analyses of the reaction mixtures revealed the generation of product peak(s). The results were further supported by high-resolution quadruple time of flight electrospray ionization mass spectrometry analyses. The product purified from the reaction mixture with UDP-D-glucose was subjected to NMR analysis, and the structure was determined to be mupirocin 6-O-β-D-glucoside. Other glycoside analogs of mupirocin were determined based on high-resolution mass analyses. Antibacterial activity assays against Staphylococcus aureus demonstrated complete loss of antibacterial activity after glucosylation of mupirocin at the 6-hydroxyl position.

Metabolic engineering of E. coli for the production of isoflavonoid‐7‐O‐methoxides and their biological activities

Isoflavonoid representatives such as genistein and daidzein are highly potent anticancer, antibacterial, and antioxidant agents. It have been demonstrated that methylation of flavonoids enhanced the transporting ability, which lead to facilitated absorption and greatly increased bioavailability. In this paper, genetically engineered Escherichia coli was reconstructed by harboring E. coli K12‐derived metK encoding S‐adenosine‐l‐methionine (SAM) synthase (accession number: K02129) for enhancement of SAM as a precursor and Streptomyces avermitilis originated SaOMT2 (O‐methyltransferase, accession number: NP_823558) for methylation of daidzein and genistein as preferred substrates. The formation of desired products via biotransformation including 4′‐O‐methyl‐genistein and 4′‐O‐methyl‐daidzein was confirmed individually by using chromatographical methods such as high‐performance liquid chromatography, liquid chromatography/time‐of‐flight/mass spectrometry (LC‐TOF‐MS), and nuclear magnetic resonance (NMR), and NMR (1H and 13C). Furthermore, substrates concentration, incubation time, and media parameters were optimized using flask culture. Finally, the most fit conditions were applied for fed‐batch fermentation with scale‐up to 3 L (working volume) to obtain the maximum yield of the products including 164.25 µM (46.81 mg/L) and 382.50 µM (102.88 mg/L) for 4′‐O‐methyl genistein and 4′‐O‐methyl daidzein, respectively. In particular, potent inhibitory activities of those isoflavonoid methoxides against the growth of cancer line (B16F10, AGS, and HepG2) and human umbilical vein endothelial cells were investigated and demonstrated. Taken together, this research work described the production of isoflavonoid‐4′‐O‐methoxides by E. coli engineering, improvement of production, characterization of produced compounds, and preliminary in vitro biological activities of the flavonoids being manufactured.

Genetic evidence for the involvement of glycosyltransferase PdmQ and PdmS in biosynthesis of pradimicin from Actinomadura hibisca

Pradimicins are potent antifungal antibiotics with effective inhibitory effects against HIV-1. Pradimicin A consists of an unusual dihydrobenzo[α]naphthacenequinone aglycone substituted with a combination of D-alanine and two sugar moieties. Detailed genetic studies revealed most steps in pradimicin A biosynthesis, but the glycosylation mechanism remained inconclusive. The biosynthetic gene cluster of pradimicin A contains two putative glycosyltransferases, pdmQ and pdmS. However, the exact involvement of each gene in biosynthesis and the particular steps required for precise structural modification was unknown. In this study, the exact role of each gene was evaluated by insertional inactivation and complementation studies. Analysis of the metabolite from both of the disruption mutants revealed abolishment of pradimicin A and complementation resulted in the recovery of production. After deletion of pdmQ, pradimicin B was found to accumulate, whereas deletion of pdmS resulted in the accumulation of aglycone of pradimicin. Together, these results suggest that pdmS is responsible for the attachment of thomosamine to form pradimicin B which in turn is glycosylated by pdmQ to form pradimicin A. These results allowed us to deduce the exact order of terminal tailoring by glycosylation and provided insight into the mechanism of pradimicin A biosynthesis.