[Analysis of RECQL4 gene variant in a child with Rothmund-Thomson syndrome].

OBJECTIVE: To explore the genetic basis for a child with Rothmund-Thomson syndrome (RTS). METHODS: The child has featured poikeloderma, short stature, cataract, sparse hair and skeletal malformation. Peripheral blood samples of the child and her family members were collected and subjected to whole exome sequencing. Candidate variants were verified by Sanger sequencing. RESULTS: The child was found to harbor compound heterozygous variants of the RECQL4 gene, namely c.1048_1049delAG and c.2886-1G>A, among which c.2886-1G>A was unreported previously. According to the ACMG guidelines, the c.1048_1049delAG was predicted to be pathogenic (PVS1+PM3_Strong+PM2), while the c.2886-1G>A was predicted to be likely pathogenic (PVS1+PM2). CONCLUSION: The compound heterozygous variants of the RECQL4 gene probably underlay the pathogenesis of RTS in this patient. Above finding has enriched the mutational spectrum of the RECQL4 gene.

[Limiting metabolic steps in the utilization of D-xylose by recombinant Ralstonia eutropha W50-EAB].

OBJECTIVE: To further improve the efficiency of xylose fermentation by modifying the pentose phosphate pathway (PPP) and the aldehyde reductase gene h16_A3186 in Ralstonia eutropha W50-EAB. METHODS: The transketolase (tktA, cbbT2) and transaldolase (tal) gene were cloned from R. eutropha chromosome by PCR and inserted into expressing vector pBBR1MCS-3. The resulting recombinant plasmids were transformed into W50-EAB to generate W50-KAB, W50-CAB and W50-TAB, respectively. The aldehyde reductase gene h16_A3186 was shortened from 834 bp to 135 bp by in-frame deletion from strain W50-E in which the xylE gene coding for xylose transporter was chromosomally integrated to construct recombinant strain W50'-E. Then the xylAB gene coding for xylose isomerase and xylulokinase from Escherichia coli were expressed in W50'-E to generate recombinant strain W50'-EAB. Recombinant plasmid pWL1-TAL was transformed into W50'-EAB to construct the strain W50'-TAB. The fermentation characteristics of the engineered strains were investigated. RESULTS: The expression of tktA, cbbT2 and tal genes in R. eutropha W50-EAB was confirmed by enzyme assay. The deletion of h16_A3186 gene was confirmed by PCR analysis and enzyme assay. Amplification of transketolase activity in R. eutropha W50-EAB showed negative effect on cell growth and D-xylose consumption. The recombinant strain W50-TAB and W50'-EAB exhibited a faster growth than W50-EAB with the maximum specific growth rate of 0.039 h(-1) and 0.040 h(-1), respectively, when cultivated on 0.1 mol/L D-xylose. And the PHB accumulation of W50-TAB and W50'-EAB reached 16.2 ± 1.01% and 19.8 ± 1.05% on the basis of cell dry weight, respectively. Furthermore, recombinant strain W50'-TAB exhibited better fermentation performance with the maximum specific growth rate of 0.042 h(-1) and PHB content of 27.9 ± 0.47%, respectively. Meanwhile, the recombinant strains W50-TAB, W50'-EAB and W50'-TAB showed higher biomass and more PHB accumulation when using glucose (0.01 mol/L) and D-xylose (0.09 mol/L) mixed sugars as fermentative substrate. CONCLUSION: Overexpression of the tal gene resulted in incressed D-xylose consumption. Deficiency of the aldehyde reductase relieved inhibition to D-xylose metabolism. Combination of the two strategies contributed to a higher efficiency of D-xylose utilisation and more PHB accumulation of the engineered R. eutropha strain.

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.

[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 an L-arabinose metabolic pathway in Ralstonia eutropha W50].

OBJECTIVE: To broaden the substrate spectrum including L-arabinose, Ralstonia eutropha W50, a mutant strain with high yield of poly-beta-hydroxybutyrate (PHB), was metabolically engineered by expressing the genes encoding L-arabinose catabolic enzymes and high-affinity L-arabinose transporter from Escherichia coli. METHODS: The promoter fragment of PHB synthase gene phaC1 (P(pha C1)) from R. eutropha H16 and the araBAD genes from E. coli W3110 were cloned by PCR and inserted into expression vector pBBR1 MCS. The resulting recombinant plasmid was transformed into W50 to generate W50-1. The araFGH gene from E. coli W3110 was introduced into W50-1 by plasmid system or homologous recombination, yielding W50-2 and W50-3 respectively. The fermentation characteristics of the three engineered strains were investigated. RESULTS: The flask fermentation experiments of the engineered strains show that W50-1 carrying the arabinose catabolic genes under the control of P(pha C1) could grow in the fermentation medium containing 0.1 mol/L arabinose as the sole carbon source, but could not utilize low concentration arabinose (0.01 mol/L). However, W50-2 and W50-3 containing the gene of high-affinity arabinose transporter were able to utilize low concentration arabinose. In the fermentation medium containing 0.1 mol/L arabinose, the biomass of W50-3 was 2.5 fold higher than that of W50-1, and the PHB accumulation amount of W50-3 accounted for 38.6% of the cell dry weight. CONCLUSION: R. eutropha W50 was able to metabolize L-arabinose by the expression of araBAD genes, and the simultaneous expression of araFGH genes could further improve its ability of L-arabinose utilization. By using L-arabinose as the sole carbon source, the recombinant strain W50-3 can accumulate a noticeable level of PHB.