Project description:The strains Thermus oshimai JL-2 and Thermus thermophilus JL-18 each have a circular chromosome, 2.07 Mb and 1.9 Mb in size, respectively, and each has two plasmids ranging from 0.27 Mb to 57.2 kb. The megaplasmid of each strain contains a gene cluster for the reduction of nitrate to nitrous oxide, consistent with their incomplete denitrification phenotypes.
Project description:The complete genomes of Thermus oshimai JL-2 and T. thermophilus JL-18 each consist of a circular chromosome, 2.07 Mb and 1.9 Mb, respectively, and two plasmids ranging from 0.27 Mb to 57.2 kb. Comparison of the T. thermophilus JL-18 chromosome with those from other strains of T. thermophilus revealed a high degree of synteny, whereas the megaplasmids from the same strains were highly plastic. The T. oshimai JL-2 chromosome and megaplasmids shared little or no synteny with other sequenced Thermus strains. Phylogenomic analyses using a concatenated set of conserved proteins confirmed the phylogenetic and taxonomic assignments based on 16S rRNA phylogenetics. Both chromosomes encode a complete glycolysis, tricarboxylic acid (TCA) cycle, and pentose phosphate pathway plus glucosidases, glycosidases, proteases, and peptidases, highlighting highly versatile heterotrophic capabilities. Megaplasmids of both strains contained a gene cluster encoding enzymes predicted to catalyze the sequential reduction of nitrate to nitrous oxide; however, the nitrous oxide reductase required for the terminal step in denitrification was absent, consistent with their incomplete denitrification phenotypes. A sox gene cluster was identified in both chromosomes, suggesting a mode of chemolithotrophy. In addition, nrf and psr gene clusters in T. oshmai JL-2 suggest respiratory nitrite ammonification and polysulfide reduction as possible modes of anaerobic respiration.
Project description:A novel gene cluster involved in the degradation of lignin-derived monoaromatics such as p-hydroxybenzoate, vanillate, and ferulate has been identified in the thermophilic nitrate reducer Thermus oshimai JL-2. Based on conserved domain analyses and metabolic pathway mapping, the cluster was classified into upper- and peripheral-pathway operons. The upper-pathway genes, responsible for the degradation of p-hydroxybenzoate and vanillate, are located on a 0.27-Mb plasmid, whereas the peripheral-pathway genes, responsible for the transformation of ferulate, are spread throughout the plasmid and the chromosome. In addition, a lower-pathway operon was also identified in the plasmid that corresponds to the meta-cleavage pathway of catechol. Spectrophotometric and gene induction data suggest that the upper and lower operons are induced by p-hydroxybenzoate, which the strain can degrade completely within 4 days of incubation, whereas the peripheral genes are expressed constitutively. The upper degradation pathway follows a less common route, proceeding via the decarboxylation of protocatechuate to form catechol, and involves a novel thermostable γ-carboxymuconolactone decarboxylase homolog, identified as protocatechuate decarboxylase based on gene deletion experiments. This gene cluster is conserved in only a few members of the Thermales and shows traces of vertical expansion of catabolic pathways in these organisms toward lignoaromatics.IMPORTANCE High-temperature steam treatment of lignocellulosic biomass during the extraction of cellulose and hemicellulose fractions leads to the release of a wide array of lignin-derived aromatics into the natural ecosystem, some of which can have detrimental effects on the environment. Not only will identifying organisms capable of using such aromatics aid in environmental cleanup, but thermostable enzymes, if characterized, can also be used for efficient lignin valorization. However, no thermophilic lignin degraders have been reported thus far. The present study reports T. oshimai JL-2 as a thermophilic bacterium with the potential to use lignin-derived aromatics. The identification of a novel thermostable protocatechuate decarboxylase gene in the strain further adds to its significance, as such an enzyme can be efficiently used in the biosynthesis of cis,cis-muconate, an important intermediate in the commercial production of plastics.