Abstract
The marine bacterium Microbulbifer sp. A4B-17 produces secondary metabolites such as 4-hydroxybenzoic acid (4HBA) and esters of 4HBA (parabens). 4HBA is a useful material in the synthesis of the liquid crystal. Parabens are man-made compounds that have been extensively used since the 1920s in the cosmetic, pharmaceutical, and food industries for their effective antimicrobial activity. In this study, we completed the sequencing and annotation of the A4B-17 strain genome and found all genes for glucose utilization and 4HBA biosynthesis. Strain A4B-17 uses the Embden-Meyerhof-Parnas (EMP), hexose monophosphate (HMP), and Entner-Doudoroff (ED) pathways to utilize glucose. Other sugars such as fructose, sucrose, xylose, arabinose, galactose, mannitol, and glycerol supported cell growth and 4HBA synthesis. Reverse transcriptional analysis confirmed that the key genes involved in the glucose metabolism were functional. Paraben concentrations were proportionally increased by adding alcohols to the culture medium, indicating that strain A4B-17 synthesizes the 4HBA and the alcohols separately and an esterification reaction between them is responsible for the paraben synthesis. A gene that codes for a carboxylesterase was proposed to catalyze this reaction. The temperature and NaCl concentration for optimal growth were determined to be 35°C and 22.8 g/L.
Highlights
4-Hydroxybenzoic acid (4HBA) is a simple aromatic compound that is widely used in the chemical and electrical industries as a material for the production of polymers, as a monomer for the synthesis of liquid crystalline polymers (Gilkey and Caldwell, 1959). 4HBA is currently synthesized from the petroleum product benzene via cumene and phenol intermediates under high pressure and temperature with a series of chemical catalysts
The strain A4B-17 was able to grow at NaCl concentrations from 15 to 30 g/L when ONR7α was used as a base medium that was supplemented with 0.1% yeast extract and 0.5% tryptone, and the optimal growth occurred at 22.8 g/L NaCl
The synthesis of parabens is proposed to occur by the esterification of 4HBA and the relevant alcohols
Summary
4-Hydroxybenzoic acid (4HBA) is a simple aromatic compound that is widely used in the chemical and electrical industries as a material for the production of polymers, as a monomer for the synthesis of liquid crystalline polymers (Gilkey and Caldwell, 1959). 4HBA is currently synthesized from the petroleum product benzene via cumene and phenol intermediates under high pressure and temperature with a series of chemical catalysts. Mayer et al (2001) expressed the Pseudomonas fluorescens HCHL gene in tobacco cells and rerouted the plant phenylpropanoid pathway to synthesize 4HBA. To synthesize 4HBA from the renewable carbon source glucose, Barker and Frost (2001) constructed a recombinant E. coli strain that overexpressed the feedback-insensitive 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAHP) synthase, increased the expression of the shikimate pathway enzymes, and overexpressed the CPL gene (E. coli ubiC). Zhang et al (2015) designed an E. coli–E. coli coculture system that achieved a production of 2.3 g/L 4HBA using a glucose and xylose mixture One of these E. coli strains has the shikimate pathway for the synthesis of 3-dehydroshikimate, and the other has the ability to transport 3-dehydroshikimate and convert it to 4HBA
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