| Autor: |
Silva PC; CBMA - Center of Molecular and Environmental Biology, University of Minho, Campus de Gualtar, 4710-057, Braga, Portugal. pcfernandesdasilva@gmail.com., Ceja-Navarro JA; Biological Systems and Engineering, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.; Institute for Biodiversity Science and Sustainability, California Academy of Sciences, San Francisco, CA, USA., Azevedo F; CBMA - Center of Molecular and Environmental Biology, University of Minho, Campus de Gualtar, 4710-057, Braga, Portugal., Karaoz U; Earth and Environmental Sciences, Lawrence Berkeley National Laboratory, Berkeley, CA, USA., Brodie EL; Earth and Environmental Sciences, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. ELBrodie@lbl.gov.; Department of Environmental Science, Policy and Management, University of California, Berkeley, CA, USA. ELBrodie@lbl.gov., Johansson B; CBMA - Center of Molecular and Environmental Biology, University of Minho, Campus de Gualtar, 4710-057, Braga, Portugal. bjorn_johansson@bio.uminho.pt. |
| Abstrakt: |
Carbohydrate rich substrates such as lignocellulosic hydrolysates remain one of the primary sources of potentially renewable fuel and bulk chemicals. The pentose sugar D-xylose is often present in significant amounts along with hexoses. Saccharomyces cerevisiae can acquire the ability to metabolize D-xylose through expression of heterologous D-xylose isomerase (XI). This enzyme is notoriously difficult to express in S. cerevisiae and only fourteen XIs have been reported to be active so far. We cloned a new D-xylose isomerase derived from microorganisms in the gut of the wood-feeding beetle Odontotaenius disjunctus. Although somewhat homologous to the XI from Piromyces sp. E2, the new gene was identified as bacterial in origin and the host as a Parabacteroides sp. Expression of the new XI in S. cerevisiae resulted in faster aerobic growth than the XI from Piromyces on D-xylose media. The D-xylose isomerization rate conferred by the new XI was also 72% higher, while absolute xylitol production was identical in both strains. Interestingly, increasing concentrations of xylitol (up to 8 g L -1 ) appeared not to inhibit D-xylose consumption. The newly described XI displayed 2.6 times higher specific activity, 37% lower K M for D-xylose, and exhibited higher activity over a broader temperature range, retaining 51% of maximal activity at 30 °C compared with only 29% activity for the Piromyces XI. |
