Fermentative production of 1-propanol from sugars using wild-type and recombinant Shimwellia blattae

Large-scale preparation of yeast strains expressing condensates derived from a glycolytic enzyme via controlled dissolved oxygen levels under hypoxia

Under hypoxia, Saccharomyces cerevisiae forms cytoplasmic condensates composed of proteins, including glycolytic enzymes, that are thought to regulate cellular metabolism. However, the hypoxic conditions required for condensate formation remain unclear. In this study, we developed a 300-mL-scale culture method to produce condensate-forming cells by precisely controlling the dissolved oxygen (DO) level in the media. Using enolase as a model, a foci formation rate of more than 50% was achieved at ∼0.1% DO, and the results showed that the DO level affected the foci formation rate. The foci formation rates of the previously reported foci-deficient strains and strains with single amino acid substitutions in the endogenous enolase were examined, and the effect of these amino acid substitutions on glucose consumption and ethanol and glycerol production under hypoxia was evaluated. The results of this study contribute to the investigation of the mechanisms that regulate biomacromolecular condensates under hypoxia.

Foci-forming regions of pyruvate kinase and enolase at the molecular surface incorporate proteins into yeast cytoplasmic metabolic enzymes transiently assembling (META) bodies

Spatial reorganization of metabolic enzymes to form the "metabolic enzymes transiently assembling (META) body" is increasingly recognized as a mechanism contributing to regulation of cellular metabolism in response to environmental changes. A number of META body-forming enzymes, including enolase (Eno2p) and phosphofructokinase, have been shown to contain condensate-forming regions. However, whether all META body-forming enzymes have condensate-forming regions or whether enzymes have multiple condensate-forming regions remains unknown. The condensate-forming regions of META body-forming enzymes have potential utility in the creation of artificial intracellular enzyme assemblies. In the present study, the whole sequence of yeast pyruvate kinase (Cdc19p) was searched for condensate-forming regions. Four peptide fragments comprising 27-42 amino acids were found to form condensates. Together with the fragment previously identified from Eno2p, these peptide regions were collectively termed "META body-forming sequences (METAfos)." METAfos-tagged yeast alcohol dehydrogenase (Adh1p) was found to co-localize with META bodies formed by endogenous Cdc19p under hypoxic conditions. The effect of Adh1p co-localization with META bodies on cell metabolism was further evaluated. Expression of Adh1p fused with a METAfos-tag increased production of ethanol compared to acetic acid, indicating that spatial reorganization of metabolic enzymes affects cell metabolism. These results contribute to understanding of the mechanisms and biological roles of META body formation.

Modulating redox metabolism to improve isobutanol production in Shimwellia blattae

BACKGROUND

Isobutanol is a candidate to replace gasoline from fossil resources. This higher alcohol can be produced from sugars using genetically modified microorganisms. Shimwellia blattae (p424IbPSO) is a robust strain resistant to high concentration of isobutanol that can achieve a high production rate of this alcohol. Nevertheless, this strain, like most strains developed for isobutanol production, has some limitations in its metabolic pathway. Isobutanol production under anaerobic conditions leads to a depletion of NADPH, which is necessary for two enzymes in the metabolic pathway. In this work, two independent approaches have been studied to mitigate the co-substrates imbalance: (i) using a NADH-dependent alcohol dehydrogenase to reduce the NADPH dependence of the pathway and (ii) using a transhydrogenase to increase NADPH level.

RESULTS

The addition of the NADH-dependent alcohol dehydrogenase from Lactococcus lactis (AdhA) to S. blattae (p424IbPSO) resulted in a 19.3% higher isobutanol production. The recombinant strain S. blattae (p424IbPSO, pIZpntAB) harboring the PntAB transhydrogenase produced 39.0% more isobutanol than the original strain, reaching 5.98 g L^-1 of isobutanol. In both strains, we observed a significant decrease in the yields of by-products such as lactic acid or ethanol.

CONCLUSIONS

The isobutanol biosynthesis pathway in S. blattae (p424IbPSO) uses the endogenous NADPH-dependent alcohol dehydrogenase YqhD to complete the pathway. The addition of NADH-dependent AdhA leads to a reduction in the consumption of NADPH that is a bottleneck of the pathway. The higher consumption of NADH by AdhA reduces the availability of NADH required for the transformation of pyruvate into lactic acid and ethanol. On the other hand, the expression of PntAB from E. coli increases the availability of NADPH for IlvC and YqhD and at the same time reduces the availability of NADH and thus, the production of lactic acid and ethanol. In this work it is shown how the expression of AdhA and PntAB enzymes in Shimwellia blattae increases yield from 11.9% to 14.4% and 16.4%, respectively.

Genomic Analysis of Microbulbifer sp. Strain A4B-17 and the Characterization of Its Metabolic Pathways for 4-Hydroxybenzoic Acid Synthesis

The marine bacterium Microbulbifer sp. A4B-17 produces secondary metabolites such as 4-hydroxybenzoic acid (4HBA) and esters of 4HBA (parabens). 4HBA is a useful material in the synthesis of the liquid crystal. Parabens are man-made compounds that have been extensively used since the 1920s in the cosmetic, pharmaceutical, and food industries for their effective antimicrobial activity. In this study, we completed the sequencing and annotation of the A4B-17 strain genome and found all genes for glucose utilization and 4HBA biosynthesis. Strain A4B-17 uses the Embden-Meyerhof-Parnas (EMP), hexose monophosphate (HMP), and Entner-Doudoroff (ED) pathways to utilize glucose. Other sugars such as fructose, sucrose, xylose, arabinose, galactose, mannitol, and glycerol supported cell growth and 4HBA synthesis. Reverse transcriptional analysis confirmed that the key genes involved in the glucose metabolism were functional. Paraben concentrations were proportionally increased by adding alcohols to the culture medium, indicating that strain A4B-17 synthesizes the 4HBA and the alcohols separately and an esterification reaction between them is responsible for the paraben synthesis. A gene that codes for a carboxylesterase was proposed to catalyze this reaction. The temperature and NaCl concentration for optimal growth were determined to be 35°C and 22.8 g/L.

Biosynthesis of hydrocarbons and volatile organic compounds by fungi: bioengineering potential

Recent advances in the biological production of fuels have relied on the optimization of pathways involving genes from diverse organisms. Several recent articles have highlighted the potential to expand the pool of useful genes by looking to filamentous fungi. This review highlights the enzymes and organisms used for the production of a variety of fuel types and commodity chemicals with a focus on the usefulness and promise of those from filamentous fungi.