A unique pattern of toxic synthesis in pentitol catabolism: Implications for evolution

Scangos, G A; Reiner, Albey M.

doi:10.1007/bf01732338

Cited by 9 publications

(11 citation statements)

References 20 publications

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“…Similar effects have been described for E. coli C (Scangos and Reiner 1979) and for lactobacilli growing in the presence of two different alditols (London 1990). The target for xylitol phosphate inhibition has not yet been detected.…”

Section: Discussionsupporting

confidence: 53%

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Pentose metabolism in Zymomonas mobilis wild-type and recombinant strains

Feldmann

Sahm

Sprenger

1992

Appl Microbiol Biotechnol

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The enzyme activities of the pentose phosphate pathway in the ethanologenic, Gram-negative bacterium Zymomonas mobilis were studied in order to construct a xylose catabolic pathway. I n cell-free extracts of wild-type Z. mobilis CP4, activities of the enzymes transketolase (TKT) [2 munits (U)/mg], phosphoribose epimerase (640mU/mg), phosphoribose isomerase (1600mU/mg) and 6-phosphogluconate dehydrogenase (2 mU/mg) were determined. However, no transaldolase activity could be detected. Recombinant strains of Z. mobilis were constructed that carried the xylAB genes of the xylose catabolic pathway from Klebsiella pneumoniae. Expression of xylose isomerase (XI, 150 mU/mg) and xylulokinase (XK) (1300 mU/mg) were found in recombinant strains but no growth on pentose as sole carbon source occurred. The xyl-recombinant cells were moreover growth-inhibited in the presence of xylose and were found to accumulate xylitol phosphate due to the subsequent action Of a novel enzyme, an NADPH-dependent aldose reductase, and a side reaction of XK on xylitol. From the xylAB recombinant strains, mutants were isolated that were less inhibited and formed less xylitol phosphate when grown in the presence of xylose. The tkt gene of E. coli was cloned on the xylAB plasmid and introduced into Z. mobilis strains. This led to higher TKT activities (150 mU/mg) and, in cooperation with the enzymes XI and XK, mediated a conversion of small amounts of xylose to CO2 and ethanol. However, no growth on xylose as sole carbon source was detected, instead sedoheptulose 7-P accumulated intracellularly.

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Section: Discussionsupporting

confidence: 53%

“…This accumulation correlated with growth inhibition. Similar inhibiting effects of non-metabolizable polyol phosphates have been described before, in the case of lactobacilli (London 1990) and in E. coli C strains with defects in polyol metabolism (Scangos and Reiner 1979).…”

Section: Expression Of Xylose Catabolic Genes In Z Mobilissupporting

confidence: 54%

Pentose metabolism in Zymomonas mobilis wild-type and recombinant strains

Feldmann

Sahm

Sprenger

1992

Appl Microbiol Biotechnol

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“…At a metabolite level, it was observed that A3 produced much less xylitol during xylose fermentation. As previously suggested by other researchers (Feldmann et al, 1992;Jeon et al, 2005;Kim et al, 2000;Scangos and Reiner, 1979), xylitol formation and its toxicity may be an important factor. This was investigated as a potential reason for the improvement in A3.…”

Section: Reduced Xylitol Production and Increased Xylitol Tolerance Imentioning

confidence: 65%

Adaptation yields a highly efficient xylose‐fermenting Zymomonas mobilis strain

Agrawal

Mao

Chen

2010

Biotech & Bioengineering

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Zymomonas mobilis is a superb ethanol producer with productivity exceeding yeast strains by several fold. Although metabolic engineering was successfully applied to expand its substrate range to include xylose, xylose fermentation lagged far behind glucose. In addition, xylose fermentation was often incomplete when its initial concentration was higher than 5%. Improvement of xylose fermentation is therefore necessary. In this work, we applied adaptation to improve xylose fermentation in metabolically engineered strains. As a result of adaptation over 80 days and 30 serial transfers in a medium containing high concentration of xylose, a strain, referred as A3, with markedly improved xylose metabolism was obtained. The strain was able to grow on 10% (w/v) xylose and rapidly ferment xylose to ethanol within 2 days and retained high ethanol yield. Similarly, in mixed glucose-xylose fermentation, a total of 9% (w/v) ethanol was obtained from two doses of 5% glucose and 5% xylose (or a total of 10% glucose and 10% xylose). Further investigation reveals evidence for an altered xylitol metabolism in A3 with reduced xylitol formation. Additionally xylitol tolerance in A3 was increased. Furthermore, xylose isomerase activity was increased by several times in A3, allowing cells to channel more xylose to ethanol than to xylitol. Taken together, these results strongly suggest that altered xylitol metabolism is key to improved xylose metabolism in adapted A3 strain. This work further demonstrates that adaptation and metabolic engineering can be used synergistically for strain improvement.

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“…Thus, based on biochemical studies, both catabolic pathways are highly similar in Klebsiella ( Fig. 1) and in E. coZi C (Reiner, 1975), and based on genetic studies the operons are very similar in both organisms and are located at a similar place in the chromosome (Scangos & Reiner, 1979). We cloned the at1 and rtl genes from E. coli C and were able to show that they map in both organisms at an identical location, that is between the attP2I site and the d h n A gene (Fig.…”

Section: Discussionmentioning

confidence: 91%

“…Among the many pentoses, pentitols and hexitols, only ~-xylulose [ K M a P P 0.8 m M ; Vmax 150 pmol min-' (mg protein)-'] is a substrate for DalK (Hartley, 1984b). It has been claimed that XylB accepts D-arabinitol and produces Darabinitol 5-phosphate (Scangos & Reiner, 1979). The three kinases belong to the prokaryotic D-xylulokinase group of the hexokinase family as defined by Bork et al (1993) (Hartley, 1984b).…”

Section: Dalr and Rbtr Encoding Repressors Dalr And Rbtrmentioning

confidence: 99%

Genes for D-arabinitol and ribitol catabolism from Klebsiella pneumoniae

et al. 1998

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The enzymes for catabolism of the pentitols D-arabinitol (Dal) and ribitol (Rbt) and the corresponding genes from Klebsiella pneurnoniae (dal and rbt) and Escherichia coli (at/ and rtl) have been used intensively in experimental evolutionary studies. Four dal and four rbt genes from the chromosome of K. pneurnoniae 1033-5P14 were cloned and sequenced. These genes are clustered in two adjacent but divergently transcribed operons and separated by two convergently transcribed repressor genes, dalR and rbtR. Each operon encodes an NAD-dependent pentose dehydrogenase (dalD and rbtl)), an ATP-dependent pentulose kinase (dalK and rbtK) and a pentose-specif ic ion symporter (dalT and rbtl). Although the biochemical reactions which they catalyse are highly similar, the enzymes showed interesting deviations. Thus, DalR (313 aa) and RbtR (270 aa) belong to different repressor families, and DalD (455 aa) and RbtD (248 aa), which are active as a monomer or as tetramers, respectively, belong to different dehydrogenase families. Of the two kinases (19.3% identity), DalK (487 aa) belongs to the subfamily of short 0-xylulokinases and RbtK (D-ribulokinase; 535 aa) to the subfamily of long kinases. The repressor, dehydrogenase and kinase genes did not show extensive similarity beyond local motifs. This contrasts with the ion symporters (86.6 Yo identity) and their genes (8207% identity). Due to their unusually high similarity, parts of dalT and rbtT have previously been claimed erroneously to correspond to 'inverted repeats' and possible remnants of a 'metabolic transposon' comprising the dal and rbt genes. Other characteristic structures, e.g. a secondary attl site and chi-like sites, as well as the conservation of this gene group in E. coli C are also discussed.

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A unique pattern of toxic synthesis in pentitol catabolism: Implications for evolution

Cited by 9 publications

References 20 publications

Pentose metabolism in Zymomonas mobilis wild-type and recombinant strains

Pentose metabolism in Zymomonas mobilis wild-type and recombinant strains

Adaptation yields a highly efficient xylose‐fermenting Zymomonas mobilis strain

Genes for D-arabinitol and ribitol catabolism from Klebsiella pneumoniae

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