Backgroundp-Hydroxycinnamic acid (pHCA) is an aromatic compound that serves as a starting material for the production of many commercially valuable chemicals, such as fragrances and pharmaceuticals, and is also used in the synthesis of thermostable polymers. However, chemical synthesis of pHCA is both costly and harmful to the environment. Although pHCA production using microbes has been widely studied, there remains a need for more cost-effective methods, such as the use of biomass as a carbon source. In this study, we produced pHCA using tyrosine ammonia lyase-expressing Streptomyces lividans. In order to improve pHCA productivity from cellulose, we constructed a tyrosine ammonia lyase- and endoglucanase (EG)-expressing S. lividans transformant and used it to produce pHCA from cellulose.ResultsA Streptomyces lividans transformant was constructed to express tyrosine ammonia lyase derived from Rhodobacter sphaeroides (RsTAL). The transformant produced 786 or 736 mg/L of pHCA after 7 days of cultivation in medium containing 1% glucose or cellobiose as the carbon source, respectively. To enhance pHCA production from phosphoric acid swollen cellulose (PASC), we introduced the gene encoding EG into RsTAL-expressing S. lividans. After 7 days of cultivation, this transformant produced 753, 743, or 500 mg/L of pHCA from 1% glucose, cellobiose, or PASC, respectively.ConclusionsRsTAL-expressing S. lividans can produce pHCA from glucose and cellobiose. Similarly, RsTAL- and EG-expressing S. lividans can produce pHCA from glucose and cellobiose with excess EG activity remaining in the supernatant. This transformant demonstrated improved pHCA production from cellulose. Further enhancements in the cellulose degradation capability of the transformant will be necessary in order to achieve further improvements in pHCA production from cellulose.

The gasification characteristics of five amino acids, i.e., glycine, alanine, valine, leucine, and proline, in supercritical water were compared. A tubular reactor was employed for the gasification reactions in the temperature range of 500 to 650 ℃ with a reaction pressure of 25 MPa and residence time of 86-119 s. The gasification characteristics of glycine, alanine, and leucine were determined to be similar, while the gasification rate of valine was much slower. The activation energies of valine and proline were lower than those of glycine, alanine, and leucine. These behaviors are attributed to the stability of the transition state for carboxyl radical production and secondary radical produced from valine.

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Effect of organic acids on char suppression in supercritical water gasification (SCWG) was investigated. When acetic acid or formic acid was added to the SCWG of guaiacol, char production was suppressed. Acetic acid also effectively suppressed char formation in the SCWG of a Shochu residue. When an optimal amount of acetic acid was added, char production was drastically suppressed, while hydrogen was produced in excess of the added acetic acid. Further addition of acetic acid increased the char production as well as the production of methane and carbon dioxide. We believe that the organic acids function as radical scavengers to suppress char formation that usually occurs via a radical mechanism.

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