Biosynthesis of adipic acid via microaerobic hydrogenation of cis,cis-muconic acid by oxygen-sensitive enoate reductase.

Adipic acid (AA) is an important dicarboxylic acid used for the manufacture of nylon and polyurethane plastics. In this study, a novel adipic acid biosynthetic pathway was designed by extending the cis,cis-muconic acid (MA) biosynthesis through biohydrogenation. Enoate reductase from Clostridium acetobutylicum (CaER), an oxygen-sensitive reductase, was demonstrated to have in vivo enzyme activity of converting cis,cis-muconic acid to adipic acid under microaerobic condition. Engineered Escherichia coli strains were constructed to express the whole pathway and accumulated 5.8 ±â€¯0.9 mg/L adipic acid from simple carbon sources. Considering the different oxygen demands between cis,cis-muconic acid biosynthesis and its degradation, a co-culture system was constructed. To improve production, T7 promoter instead of lac promoter was used for higher level expression of the key enzyme CaER and the titer of adipic acid increased to 18.3 ±â€¯0.6 mg/L. To decrease the oxygen supply to downstream strains expressing CaER, Vitreoscilla hemoglobin (VHb) was introduced to upstream strains for its ability on oxygen obtaining. This attempt further improved the production of this novel pathway and 27.6 ±â€¯1.3 mg/L adipic acid was accumulated under microaerobic condition.

Peroxynitrite scavenging by Campylobacter jejuni truncated hemoglobin P.

Truncated hemoglobins (trHb) are present in protozoa, cyanobacteria, nemertean, bacteria, algae, and plants. They are characterized by the 2-on-2 topology and are ordered in four phylogenetic groups (I or N, II or O, III or P, and IV or Q). Several functions have been attributed to trHbs including the inactivation of reactive nitrogen and oxygen species, permitting the survival of microorganisms in the host. Here, the kinetics of peroxynitrite scavenging by ferric Campylobacter jejuni truncated hemoglobin P [i.e., Cj-trHbP(III)] in the absence and presence of CO2, between pH 6.3 and 7.9, and 25.0 °C, is reported. Mixing the Cj-trHbP(III) solution with peroxynitrite solution brings about absorption spectral changes at 302 nm reflecting the disappearance of this endogenous toxicant and cytotoxic effector against pathogens. CO2 affects only the rate of spontaneous decay of peroxynitrite without affecting the scavenging activity of Cj-trHbP(III). Moreover, the Cj-trHbP(III)-mediated isomerization of peroxynitrite is facilitated at low pH, indicating that peroxynitrous acid is the reactive species. The high reactivity of Cj-trHbP(III) towards peroxynitrite has been ascribed to the peroxidase-like geometry of the metal center. To investigate the protective role of Cj-trHbP(III) against peroxynitrite-mediated nitration, the relative yield of nitro-L-tyrosine formed by the reaction of peroxynitrite with free L-tyrosine was determined. According to fast kinetics of peroxynitrite isomerization by Cj-trHbP(III), this 2-on-2 globin impairs L-tyrosine nitrosylation. Present data suggest that Cj-trHbP could help the survival of C. jejuni.