The subgenomes show asymmetric expression of alleles in hybrid lineages of Megalobrama amblycephala × Culter alburnus.

Hybridization drives rapid speciation by shaping novel genotypic and phenotypic profiles. Genomic incompatibility and transcriptome shock have been observed in hybrids, although this is rarer in animals than in plants. Using the newly sequenced genomes of the blunt snout bream (Megalobrama amblycephala [BSB]) and the topmouth culter (Culter alburnus [TC]), we focused on the sequence variation and gene expression changes in the reciprocal intergeneric hybrid lineages (F1-F3) of BSB × TC. A genome-wide transcriptional analysis identified 145-974 expressed recombinant genes in the successive generations of hybrid fish, suggesting the rapid emergence of allelic variation following hybridization. Some gradual changes of gene expression with additive and dominance effects and various cis and trans regulations were observed from F1 to F3 in the two hybrid lineages. These asymmetric patterns of gene expression represent the alternative strategies for counteracting deleterious effects of the subgenomes and improving adaptability of novel hybrids. Furthermore, we identified positive selection and additive expression patterns in transforming growth factor, beta 1b (tgfb1b), which may account for the morphological variations of the pharyngeal jaw in the two hybrid lineages. Our current findings provide insights into the evolution of vertebrate genomes immediately following hybridization.

[Engineering of a D-xylose metabolic pathway in eutropha W50].

OBJECTIVE: This study aimed to broaden the substrate spectrum of Ralstonia eutropha W50 to use D-xylose, which can produce poly-beta-hydroxybutyrates (PHB) at a high level. METHODS: The D-xylose transporter gene xylE from Escherichia coli K-12 W3110 was cloned by PCR technique and integrated into the R. eutropha W50 chromosome. The recombinant strain W50-E was obtained. The D-xylose catabolic genes xylAB from E. coli K-12 W3110 and the promotor of PHA synthase gene phaC1 from R. eutropha H16 were cloned into pBBR1MCS to construct a recombinant plasmid. The plasmid was transformed into R. eutropha W50 and W50-E to generate the recombinant strains W50-AB and W50-EAB respectively. The characteristics of D-xylose utilization by W50-AB and W50-EAB were investigated. RESULTS: The expression of xylA and xylB genes in R. eutropha W50 was confirmed by enzyme assay. The recombinant strain W50-AB could grow on 0.1 mol/L D-xylose with the maximum specific growth rate of 0.025 h(-1), but no growth and D-xylose consumption were observed when cultivated on 0.01 mol/L D-xylose. The recombinant strain W50-EAB exhibited a faster growth than W50-AB on 0.1 mol/L D-xylose, with the maximum specific growth rate of 0.035 h(-1). Furthermore, it exhibited a slow but defined growth and D-xylose consumption on 0.01 mol/L D-xylose. The PHB content assay showed that both recombinant strains accumulated a small amount of PHB, with a proportion of 15.07 +/- 1.01% and 15.07 +/- 1.64% on the basis of dry cell weight respectively, by using D-xylose (0.1 mol/L) as substrate. And their final D-xylose-PHB conversion rates were 0.0920 g x g(-1) and 0.0838 g x g(-1) respectively, which were much lower than their glucose-PHB conversion rates( > 0.22 g x g(-1)). However, the recombinant strains W50-AB and W50-EAB exhibited better fermentation performance and more PHB accumulation when using glucose(0.01 mol/L) and D-xylose (0.09 mol/L) mixed sugars as fermentative substrate. CONCLUSION: The recombinant strain W50-AB can metabolize D-xylose by the expression of xylAB genes, and the further expression of xylE gene is able to improve its D-xylose consumption rate. Meanwhile, the two recombinant strains can accumulate a small amount of PHB by using D-xylose as the sole carbon source.

Engineering of Ralstonia eutropha for the production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) from glucose.

Production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with Ralstonia eutropha relies on the addition of propionate during fermentation, and propionate consumption is one of the major factors affecting the cost of PHBV production. In this study, 7 strains were obtained by genetic manipulating the methylcitric acid cycle and the methylmalonyl-CoA pathway in R. eutropha. Disruption of prpC1 and prpC2 genes did not affect cell growth and PHBV accumulation. All 7 strains were able to accumulation high amounts of PHBVs with 3HV fractions of 0.41-29.1 mol% during cultivation in flasks. Fermentation in 7.5-L fermenter showed that genetically engineered Rem-8 was able to yield biomass of 132.8 CDWg/L, of which 68.6% were PHBV with 3HV fraction of 26.0 mol% in the biopolymer, indicating promising potentials of commercialization in the future.

Draft Genome Sequences of Two Clinical Isolates of Streptococcus mutans.

We report the draft genome sequences of PKUSS-HG01 and PKUSS-LG01, two clinical isolates of Streptococcus mutans from human dental plaque. The genomics information will facilitate the study of the mechanisms of pathogenicity and evolution of S. mutans.