Identification and functional expression of a new xylose isomerase from the goat rumen microbiome in Saccharomyces cerevisiae

The current climate crisis demands replacement of fossil energy sources with sustainable alternatives. In this scenario, second-generation bioethanol, a product of lignocellulosic biomass fermentation, represents a more sustainable alternative. However, Saccharomyces cerevisiae cannot metabolize pentoses, such as xylose, present as a major component of lignocellulosic biomass. Xylose isomerase (XI) is an enzyme that allows xylose consumption by yeasts, because it converts xylose into xylulose, which is further converted to ethanol by the pentose-phosphate pathway. Only a few XI were successfully expressed in S. cerevisiae strains. This work presents a new bacterial XI, named GR-XI 1, obtained from a Brazilian goat rumen metagenomic library. Phylogenetic analysis confirmed the bacterial origin of the gene, which is related to Firmicutes XIs. After codon optimization, this enzyme, renamed XySC1, was functionally expressed in S. cerevisiae, allowing growth in media with xylose as sole carbon source. Overexpression of XySC1 in S. cerevisiae allowed the recombinant strain to efficiently consume and metabolize xylose under aerobic conditions.     

The systematic position of Lauroiinae Skrjabin and Schikhobalova, 1951 (Nemata: Heterakoidea: Aspidoderidae), as revealed by the analysis of traits used in its diagnosis

During our work on biodiversity of parasites of mammals of the Neotropics we collected numerous nematodes assignable to species of the family Aspidoderidae (Nemata: Heterakoidea). These nematodes occur as parasites of the cecum and large intestine of marsupials, rodents and xenarthrans (armadillos) only in the New World. As aspidoderid nematodes have been little studied beyond their alpha taxonomy, it is the purpose of the present paper to apply phylogenetic systematic methods to more completely understand the evolutionary relationships of the included species. Members of the aspidoderid subfamily Lauroiinae have had very little work applied to their systematic relationships and no systematic revisions exist that include all recognized species. Diagnostic characters that define species in this subfamily include plate-like cuticular structures on the anterior end. Herein we define a suite of 52 characters derived from studies of specimens using both light and electron microscopy. Our phylogenetic systematic analysis included the eight known species in the Lauroiinae, seven of the Aspidoderinae and four outgroup taxa. The results indicate that the Lauroiinae is paraphyletic, that the cephalic plates on the anterior end are not synapomorphies for the Lauroiinae, and that structures forming the cordon are present in all species of the family. We propose elimination of the subfamily designations in the family Aspidoderidae and we show the utility of using additional characters in the diagnosis of the family and the genera within this family. The resulting hypothesis should serve as the foundation to understand the historical associations of the nematodes with the mammals they infect.
© The Willi Hennig Society 2008.