Microbial Production of Xylitol From Oil Palm Empty Fruit Bunch Hydrolysate: Effects of Inoculum and PH

Considering its high content of hemicellulose, oil palm empty fruit bunch (EFB) lignocellulosic biomass waste from palm oil processing has the potential to be utilized as the raw material for the production of xylitol, a low calorie, low GI, and anti cariogenic alternative sugar with similar sweetness to sucrose. This research explored the possibility of converting EFB to xylitol via green microbial fermentation, in particular the effects of inoculum and initial pH on the fermentation performance. It was observed that the cell concentration in the inoculum and the initial pH affect cell growth and xylitol production. pH 5 was observed to give the best fermentation performance. Further, the fermentation tended to yield more xylitol at higher initial cell concentration. It was also observed that no growth or fermentation inhibitory compounds were found in the EFB hydrolysate obtained from enzymatic hydrolysis of EFB. Thus it can be used directly as substrate for xylitol fermentation

Microbial production of curcumin

First Online: 01 October 2022Curcumin, a polyphenol produced by turmeric (Curcuma longa), has attracted increased attention due to its potential as a novel cancer-fighting drug. However, to satisfy the required curcumin demand for health-related studies, high purity curcumin preparations are required, which are difficult to obtain and are very expensive. Curcumin and other curcuminoids are usually obtained through plant extraction. However, these polyphenols accumulate in low amounts over long periods in the plant and their extraction process is costly and not environmentally friendly. In addition, curcumin chemical synthesis is complex. All these reasons limit the advances in studies related to the in vitro and in vivo curcumin biological activities. The microbial production of curcumin appears as a solution to overcome the limitations associated with the currently used methods. Curcumin biosynthesis begins with the conversion of the aromatic amino acids, phenylalanine and tyrosine, into phenylpropanoids, the curcuminoid precursors. The phenylpropanoids are then activated through condensation with a CoA molecule. Afterwards, curcuminoids are synthesized by the action of type III polyketide synthases (PKS) that combine two activated phenylpropanoids and a malonyl-CoA molecule. To engineer microbes to produce curcumin, the curcuminoid biosynthetic genes must be introduced as microorganisms lack the enzymatic reactions responsible to synthesize curcuminoids. In this chapter, the advances regarding the microbial production of curcumin are exposed. The heterologous production of curcumin has been mainly achieved in the bacteria Escherichia coli. However, other microorganisms have already been explored. Besides the introduction of curcumin biosynthetic genes, the optimization of the microbial chassis must also be considered to maximize the production yields. The strategies employed for this purpose are also herein presented. The maximum titer of curcumin produced by a genetically engineered E. coli was 563.4 mg/L with a substrate conversion yield of 100% from supplemented ferulic acid. Moreover, the de novo production of curcumin was accomplished in E. coli reaching 3.8 mg/L of curcumin. Overall, the recent developments on curcumin heterologous production are very encouraging.This study was supported by the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UIDB/BIO/04469/2020 unit, and by LABBELS – Associate Laboratory in Biotechnology, Bioengineering and Microelectromechnaical Systems, LA/P/0029/2020. J.R. is recipient of a doctoral fellowship (SFRH/BD/138325/2018) supported by a doctoral advanced training funded by FCT.info:eu-repo/semantics/publishedVersio

Microbial production of caffeic acid

First Online: 04 October 2022Caffeic acid is a hydroxycinnamic acid mostly produced in plants although its microbial production has also been reported. This compound presents several biological activities and potential therapeutic properties. Additionally, it can be a precursor or intermediary of various relevant compounds. Current production methods include the inefficient, expensive, and not environmentally friendly extraction from plants that accumulate this compound in very low amounts. Therefore, highly efficient and environmentally friendly methods are needed. Microbial biosynthesis can potentially produce it in a purer, faster, and greener way. Since the establishment of caffeic acid heterologous production in Streptomyces fradiae, several studies have been published regarding its production in Escherichia coli and Saccharomyces cerevisiae. These studies include the production from supplemented tyrosine or p-coumaric acid but also glucose using tyrosine-overproducing strains. Presently, there are three different pathways to produce caffeic acid that have in common the first step that is catalyzed by a microbial tyrosine ammonia lyase that converts tyrosine to p-coumaric acid. The second step that synthesizes caffeic acid from p-coumaric acid was identified as the pathway bottleneck and can be performed by 4-coumarate 3-hydroxylase, hydroxyphenylacetate 3-hydroxylase (4HPA3H) complex or a cytochrome P450 CYP199A2 system. Although all these enzymes have been identified in bacteria, and caffeic acid has only recently been produced in S. cerevisiae, the productions in this host have almost reached the maximum productions reported for E. coli (569 mg/L vs. 767 mg/L, respectively). The maximum production was obtained from glucose using the 4HPA3H pathway. These developments on caffeic acid heterologous production are very promising.This study was supported by the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UIDB/BIO/04469/2020 unit, and by LABBELS – Associate Laboratory in Biotechnology, Bioengineering and Microelectromechnaical Systems, LA/P/0029/2020.info:eu-repo/semantics/publishedVersio

Microbial production of advanced biofuels

Concerns over climate change have necessitated a rethinking of our transportation infrastructure. One possible alternative to carbon-polluting fossil fuels are biofuels produced from a renewable carbon source using engineered microorganisms. Two biofuels, ethanol and biodiesel, have been made inroads to displacing petroleum-based fuels, but their penetration has been limited by the amounts that can be used in conventional engines and by cost. Advanced biofuels that mimic petroleum-based fuels are not limited by the amounts that can be used in existing transportation infrastructure, but have had limited penetration due to costs. In this review, we will discuss the advances in engineering microbial metabolism to produce advanced biofuels and prospects for reducing their costs