ABSTRACT
A new beta-carotene ketolase gene (crtW) was cloned from an environmental isolate Sphingomonas sp. DC18. A robust and reliable color screen was developed for protein engineering to improve its activity on hydroxylated carotenoids for astaxanthin production. Localized random mutagenesis was performed on the crtW gene including the upstream ribosomal binding site (RBS). Six mutations (H96L, R203W, A205V, A208V, F213L and A215T) in the crtW gene were isolated multiple times that showed improved astaxanthin production. These mutations were localized near the conserved histidine motifs, which were proposed for binding iron required for enzymatic activity. Combination of two of the mutations (R203W/F213L) further improved astaxanthin production. One mutation at the RBS (a438t) was shown to have additional effect on improving astaxanthin production. Most of the mutants still retained high activity on beta-carotene, however, the F213L single mutant and the R203W/F213L double mutant that yielded the highest improvement for astaxanthin production showed decreased activity for canthaxanthin production.
Subject(s)
Bacterial Proteins/genetics , Bioreactors , Biosynthetic Pathways , Biotechnology/methods , Oxygenases/genetics , Protein Engineering/methods , Sphingomonas/enzymology , Amino Acid Sequence , Base Sequence , Carotenoids/metabolism , Cloning, Molecular , DNA Primers , Molecular Sequence Data , Mutagenesis, Site-Directed , Mutation/genetics , Sequence Alignment , Sequence Analysis, DNA , Xanthophylls/biosynthesis , Xanthophylls/chemistryABSTRACT
Biosynthesis of C(30) carotenoids is relatively restricted in nature but has been described in Staphylococcus and in methylotrophic bacteria. We report here identification of a novel gene (crtNb) involved in conversion of 4,4'-diapolycopene to 4,4'-diapolycopene aldehyde. An aldehyde dehydrogenase gene (ald) responsible for the subsequent oxidation of 4,4'-diapolycopene aldehyde to 4,4'-diapolycopene acid was also identified in Methylomonas. CrtNb has significant sequence homology with diapophytoene desaturases (CrtN). However, data from knockout of crtNb and expression of crtNb in Escherichia coli indicated that CrtNb is not a desaturase but rather a novel carotenoid oxidase catalyzing oxidation of the terminal methyl group(s) of 4,4'-diaponeurosporene and 4,4'-diapolycopene to the corresponding terminal aldehyde. It has moderate to low activity on neurosporene and lycopene and no activity on beta-carotene or zeta-carotene. Using a combination of C(30) carotenoid synthesis genes from Staphylococcus and Methylomonas, 4,4'-diapolycopene dialdehyde was produced in E. coli as the predominant carotenoid. This C30 dialdehyde is a dark-reddish purple pigment that may have potential uses in foods and cosmetics.
Subject(s)
Aldehydes/metabolism , Carotenoids/biosynthesis , Carotenoids/metabolism , Methylomonas/enzymology , Oxidoreductases/metabolism , Aldehyde Dehydrogenase/metabolism , Bacterial Proteins/genetics , Bacterial Proteins/metabolism , Carotenoids/chemistry , Escherichia coli/enzymology , Escherichia coli/genetics , Industrial Microbiology/methods , Lycopene , Methylomonas/genetics , Molecular Sequence Data , Oxidoreductases/genetics , Sequence Analysis, DNA , Substrate SpecificityABSTRACT
A polyphasic approach based on cultivation and direct recovery of 16S rRNA gene sequences was utilized for microbial characterization of an aquifer contaminated with chlorinated ethenes. This work was conducted in order to support the evaluation of natural attenuation of chlorinated ethenes in groundwater at Area 6 at Dover Air Force Base (Dover, DE). Results from these studies demonstrated the aquifer contained relatively low biomass (e.g. direct microscopic counts of < 10(7) bacteria/g of sediment) comprised of a physiologically diverse group of microorganisms including iron reducers, acetogens, sulfate reducers, denitrifiers, aerobic and anaerobic heterotrophs. Laboratory microcosms prepared with authentic sediment and groundwater provided direct microbiological evidence that the mineralization of vinyl chloride and cis-dichloroethene as well as each step in the complete reductive dechlorination of tetracloroethene to ethene can occur in the Area 6 aquifer. Enrichment cultures capable of the oxidative degradation of cis-1,2-dichloroethene (cis-DCE) and vinyl chloride (VC) were obtained from groundwater across the aquifer demonstrating the possible importance of direct, non-cometabolic oxidation of cis-DCE and VC in natural attenuation. Culture-independent analyses based upon recovery of 16S rRNA gene sequences revealed the presence of anaerobic organisms distributed primarily between two major bacterial divisions: the delta subdivision of the Proteobacteria and low-G + C gram positive. Recovery of sequences affiliated with phylogenetic groups containing known anaerobic-halorespiring organisms such as Desulfitobacterium, Dehalobacter, and certain groups of iron reducers provided qualitative support for a role of reductive dechlorination processes in the aquifer. This molecular data is suggestive of a functional linkage between the microbiology of the site and the apparent natural attenuation process. The presence and distribution of microorganisms were found to be consistent with a microbially driven attenuation of chlorinated ethenes within the aquifer and in accord with a conceptual model of aquifer geochemistry which suggest that both reductive and oxidative mechanisms are involved in heterogeneous, spatially distributed processes across the aquifer.
