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Importance of the pentose phosphate pathway for D-glucose catabolism in the obligatory aerobic yeast Rhodotorula gracilis.

ABSTRACT: d-Glucose catabolism of a phosphofructokinase-deficient yeast Rhodotorula gracilis has been studied. By using d-glucose specifically (14)C-labelled at different positions and measuring the distribution of the label in various fractions of cell metabolism, the following results were found. 1. The pentose phosphate pathway, being the main pathway of d-glucose catabolism, simultaneously converts glucose molecules into pentose phosphates oxidatively by using two NADP-linked dehydrogenases and via the non-oxidative transketolase-transaldolase pathway. 2. From the correlation of the (14)CO(2) liberation and the d-glucose consumption and from the fact that the pentose phosphate moiety in nucleic acids is almost equally labelled from d-[1-(14)C]- and d-[6-(14)C]-glucose, it is concluded that of the glucose utilized about 80% undergoes transformation via the non-oxidative pentose phosphate pathway. Only about 20% of glucose is directly decarboxylated to pentose phosphate. 3. For further degradation it is postulated that the pentose phosphates are split into C(2) fragments and glyceraldehyde 3-phosphates. 4. All three loci of oxidative decarboxylation appear to be effective in Rh. gracilis, the oxidative part of the pentose phosphate pathway, the decarboxylation of pyruvate in the later part of the glycolytic pathway as well as the oxidation in the tricarboxylic acid cycle. 5. d-Glucose molecules taken up are only partially oxidized to CO(2): about four-fifths of each glucose molecule metabolized is incorporated into cell constituents. 6. The quantitative interrelations of the fluxes of d-glucose subunits along the catabolic pathways have been estimated and are discussed.

SUBMITTER: Hofer M

PROVIDER: S-EPMC1177086 | biostudies-other | 1971 Aug

REPOSITORIES: biostudies-other

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Project description:Pseudomonas alloputida KT2440 (previously misclassified as P. putida KT2440 based on 16S rRNA gene homology) has emerged as an ideal host strain for plan t biomass valorization. However, P. alloputida KT2440 is unable to natively utilize abundant pentose sugars (e.g., xylose and arabinose) in hydrolysate streams, which may account for up to 25% of lignocellulosic biomass. In the last decades, microbes have been engineered to utilize the pentose sugars. However, most of the engineered strains were either slow-growing or displayed phenotypes that could not be replicated. In this work, we successfully isolated five Pseudomonas species with the native capability to utilize glucose, xylose and p-coumarate as a sole carbon source. These isolates were in two clusters; one set of isolates (M2 and M5) and the second set of isolates (BP6 and BP7) showed 85.6% and 96.2% ANI, respectively, to P. alloputida KT24440. BP8 showed 84.6% ANI to P. putida KT2440 and does not belong to any neighboring type strains indicating a new species. Notably, the isolates showed robust growth solely on xylose and higher growth rates (m, 0.36-0.49 h-1) when compared to only known xylose-utilizing Pseudomonas taiwanenesis VLB120 (m, 0.28 h-1) as a control. Unexpectedly, among five isolates, M2 and M5 grew solely on arabinose as well. Comprehensive analysis of genomics, transcriptomics and proteomics revealed the isolates utilize xylose and arabinose via Weimberg pathway (xylD-xylX-xylA) and oxidative pathway (araD-araX-araA), respectively. Furthermore, a preliminary result demonstrated the production of flaviolin solely on xylose and arabinose in the isolate, showing noteworthy potential to be an alternative host for lignocellulosic feedstocks into valuable products. This is the first report on isolating Pseudomonas strains natively capable of utilizing all of the major carbon sources in lignocellulosic biomass, and leading to higher consumption of available substrates and therefore maximizing the product yield.

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Importance of the pentose phosphate pathway for D-glucose catabolism in the obligatory aerobic yeast Rhodotorula gracilis.

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