Project description:Acididesulfobacillus acetoxydans is an acidophilic sulfate reducer that can dissimilatory reduce nitrate to ammonia (DNRA). However, no known nitrite reductase is encoded. This study was performed to investigate how A. acetoxydans reduces nitrate to nitrite and elucidated a novel DNRA mechanism and potential nitrosative stress resistance mechanisms in acidophiles.
Project description:In this work, we evaluated the genetic stabilization process, of the intra- (Saccharomyces cerevisiae) and interspecific (S. cerevisiae x Saccharomyces kudriavzevii) hybrids obtained by different non-GMO techniques, under fermentative conditions. Large-scale transitions in genome size, detected by measuring total DNA content, and genome reorganizations in both nuclear and mitochondrial DNA, evidenced by changes in molecular markers, were observed during the experiments. Interspecific hybrids seem to need fewer generations to reach genetic stability than intraspecific hybrids. The largest number of molecular patterns among the derived stable colonies was observed for intraspecific hybrids, particularly for those obtained by rare-mating in which the total amount of initial DNA was larger. Finally, a representative intraspecific stable hybrid underwent a normal industrial process to obtain active dry yeast production as an important point at which inducing changes in genome composition was possible. No changes in hybrid genetic composition after this procedure were confirmed by comparative genome hybridization. According to our results, fermentation steps 2 and 5 –comprising between 30 and 50 generations- suffice to obtain genetically stable interspecific and intraspecific hybrids, respectively. This work aimed to develop and validate a fast genetic stabilization method for newly generated Saccharomyces hybrids under selective enological conditions. A comparison of the whole stabilization process in intra- and interspecific hybrids showing different ploidy levels, as a result of using different hybridization methodologies, was also made.
Project description:Genome rearrangements are associated with eukaryotic evolutionary processes ranging from tumorigenesis to speciation. Such rearrangements are especially common following the shock of interspecific hybridization, and some of these could be expected to have strong selective value. To test this expectation we created de novo interspecific yeast hybrids between two diverged but largely syntenic species, Saccharomyces cerevisiae and S. uvarum, then experimentally evolved them under continuous ammonium limitation. We discovered that a characteristic interspecific genome rearrangement arose multiple times in independently evolved populations. We uncovered nine different breakpoints, all occurring in a ~1 kb region of chromosome 14, and all producing an “interspecific fusion junction” within the MEP2 gene coding sequence, such that the 5’ portion derives from S. cerevisiae and the 3’ portion derives from S. uvarum. In most cases the rearrangements altered both chromosomes, resulting in what can be considered to be an introgression of a several-kb region of S. uvarum into an otherwise intact S. cerevisiae chromosome 14, while the S. uvarum chromosome 14 experienced an interspecific reciprocal translocation at the same breakpoint within MEP2, yielding a chimaeric chromosome. The net result is the presence in the cell of two MEP2 fusion genes having identical breakpoints. Given that MEP2 encodes for a high-affinity ammonium permease, that MEP2 fusion genes arise repeatedly under ammonium-limitation, and that three independent evolved isolates carrying MEP2 fusion genes are each more fit than their common ancestor, the novel MEP2 fusion genes are very likely adaptive under ammonium limitation. Our results suggest that when homoploid hybrids form, the admixture of two genomes enables swift and otherwise unlikely evolutionary innovations. Furthermore, the architecture of the MEP2 rearrangement suggests a model for rapid introgression, a phenomenon seen in numerous eukaryotic phyla, that does not invoke repeated backcrossing to one of the parental species. Nomenclature: GSY86 TimeZeroInoculum = ancestral interspecific hybrid used to inoculate ammonium-limited chemostats into 3 replicate vessels A, B, C. 150gen = various single-clone isolates from 150 generations of evolutions from vessels A, B or C. 200gen = various isolates from 200 generations of evolutions from vessels A, B or C.