Carotenoid biosynthesis and overproduction in Corynebacterium glutamicum

Petra Peters-Wendisch,Sabine A E Heider,Volker F Wendisch

doi:10.1186/1471-2180-12-198

Abstract

BackgroundCorynebacterium glutamicum contains the glycosylated C50 carotenoid decaprenoxanthin as yellow pigment. Starting from isopentenyl pyrophosphate, which is generated in the non-mevalonate pathway, decaprenoxanthin is synthesized via the intermediates farnesyl pyrophosphate, geranylgeranyl pyrophosphate, lycopene and flavuxanthin.ResultsHere, we showed that the genes of the carotenoid gene cluster crtE-cg0722-crtBIYeYfEb are co-transcribed and characterized defined gene deletion mutants. Gene deletion analysis revealed that crtI, crtEb, and crtYeYf, respectively, code for the only phytoene desaturase, lycopene elongase, and carotenoid C45/C50 ɛ-cyclase, respectively. However, the genome of C. glutamicum also encodes a second carotenoid gene cluster comprising crtB2I2-1/2 shown to be co-transcribed, as well. Ectopic expression of crtB2 could compensate for the lack of phytoene synthase CrtB in C. glutamicum ΔcrtB, thus, C. glutamicum possesses two functional phytoene synthases, namely CrtB and CrtB2. Genetic evidence for a crtI2-1/2 encoded phytoene desaturase could not be obtained since plasmid-borne expression of crtI2-1/2 did not compensate for the lack of phytoene desaturase CrtI in C. glutamicum ΔcrtI. The potential of C. glutamicum to overproduce carotenoids was estimated with lycopene as example. Deletion of the gene crtEb prevented conversion of lycopene to decaprenoxanthin and entailed accumulation of lycopene to 0.03 ± 0.01 mg/g cell dry weight (CDW). When the genes crtE, crtB and crtI for conversion of geranylgeranyl pyrophosphate to lycopene were overexpressed in C. glutamicum ΔcrtEb intensely red-pigmented cells and an 80 fold increased lycopene content of 2.4 ± 0.3 mg/g CDW were obtained.ConclusionC. glutamicum possesses a certain degree of redundancy in the biosynthesis of the C50 carotenoid decaprenoxanthin as it possesses two functional phytoene synthase genes. Already metabolic engineering of only the terminal reactions leading to lycopene resulted in considerable lycopene production indicating that C. glutamicum may serve as a potential host for carotenoid production.

Highlights

Corynebacterium glutamicum contains the glycosylated C50 carotenoid decaprenoxanthin as yellow pigment
Bioinformatical analysis of the carotenogenic genes The genome of C. glutamicum ATCC 13032 encodes genes showing homology to carotenoid biosynthesis genes in two gene clusters that are separated by almost 2 Mbp
The second cluster consists of a gene putatively encoding phytoene synthase and two genes with similarity to an N-terminal fragment and a C-terminal fragment of phytoene desaturase/dehydrogenase (Figure 1)

Summary

Introduction

Corynebacterium glutamicum contains the glycosylated C50 carotenoid decaprenoxanthin as yellow pigment. Carotenoids are yellow to red colored pigments originating from the terpenoid biosynthetic pathway. They are very abundant in plants and microorganisms, where they can have diverse functions such as photo protection or light harvesting molecules or as membrane stabilizers [1,2]. There are two independent pathways leading to IPP: the mevalonic acid (MVA) pathway and the methylerythritol phosphate (MEP) pathway. Most bacteria as well as plant plastides synthesize IPP through the MEP pathway [1,12,13]. The MVA pathway requires acetyl-CoA as the primary educt, whereas the MEP pathway starts by condensation of pyruvate and glyceraldehyde 3-phosphate (GAP) [14,15]

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