Cyanide as a Primordial Reductant enables a Protometabolic Reductive Glyoxylate Pathway

Investigation of prebiotic chemical pathways leading to protometabolic forerunners of metabolism has been largely based on bio-inspired (iron-mediated) reductive conversion of carbon dioxide and of carboxylic acid substrates.1,2 While attractive from a parsimony point of view, this approach has been challenging with debatable outcomes.3,4 Herein, we show that cyanide reacts with citric acid cycle (TCA) intermediates and derivatives and acts as a primordial reducing agent mediating abiotic reductive transformations. The hydrolysis of the cyanide adducts followed by decarboxylation enables the efficient reductive-decarboxylative transformation of oxaloacetate to malate and fumarate to succinate while pyruvate and α-ketoglutarate are not reduced. In the presence of glyoxylate,5,6 malonate7 and malononitrile,8 alternative pathways emerge, which after decarboxylation produce metabolic intermediates and related compounds also found in meteorites.9 These results, along with the previous demonstration of the metal-free alpha-keto analog of the reverse-TCA cycle,4,6 suggest that (a) alternative paradigms of cyanide-based protometabolic reactions bypassing the abiotic reductive-carboxylation steps can be prebiotically viable, (b) a novel reductive glyoxylate pathway can be a precursor to the r-TCA cycle and (c) the type of sophisticated carboxylation and reduction chemistries which are part of extant metabolic cycles10,11 are an evolutionary invention mediated by complex metalloproteins11.

Metabolic engineering and transcriptomic analysis of Saccharomyces cerevisiae producing p-coumaric acid from xylose

Background Aromatic amino acids and their derivatives are valuable chemicals and are precursors for different industrially compounds. p-Coumaric acid is the main building block for complex secondary metabolites in commercial demand, such as flavonoids and polyphenols. Industrial scale production of this compound from yeast however remains challenging. Results Using metabolic engineering and a systems biology approach, we developed a Saccharomyces cerevisiae platform strain able to produce 242 mg/L of p-coumaric acid from xylose. The same strain produced only 5.35 mg/L when cultivated with glucose as carbon source. To characterise this platform strain further, transcriptomic analysis was performed, comparing this strain’s growth on xylose and glucose, revealing a strong up-regulation of the glyoxylate pathway alongside increased cell wall biosynthesis and unexpectedly a decrease in aromatic amino acid gene expression when xylose was used as carbon source. Conclusions The resulting S. cerevisiae strain represents a promising platform host for future production of p-coumaric using xylose as a carbon source.

A Universal Stress Protein That Controls Bacterial Stress Survival in Micrococcus luteus

ABSTRACT Bacteria have remarkable mechanisms to survive severe external stresses, and one of the most enigmatic is the nonreplicative persistent (NRP) state. Practically, NRP bacteria are difficult to treat, and so inhibiting the proteins underlying this survival state may render such bacteria more susceptible to external stresses, including antibiotics. Unfortunately, we know little about the proteins and mechanisms conferring survival through the NRP state. Here, we report that a universal stress protein (Usp) is a primary regulator of bacterial survival through the NRP state in Micrococcus luteus NCTC 2665, a biosafety level 1 (BSL1) mycobacterial relative. Usps are widely conserved, and bacteria, including Mycobacterium tuberculosis, Mycobacterium smegmatis, and Escherichia coli, have multiple paralogs with overlapping functions that have obscured their functional roles. A kanamycin resistance cassette inserted into the M. luteus universal stress protein A 616 gene (ΔuspA616::kan M. luteus) ablates the UspA616 protein and drastically impairs M. luteus survival under even short-term starvation (survival, 83% wild type versus 32% ΔuspA616::kan M. luteus) and hypoxia (survival, 96% wild type versus 48% ΔuspA616::kan M. luteus). We observed no detrimental UspA616 knockout phenotype in logarithmic growth. Proteomics demonstrated statistically significant log-phase upregulation of glyoxylate pathway enzymes isocitrate lyase and malate synthase in ΔuspA616::kan M. luteus. We note that these enzymes and the M. tuberculosis UspA616 homolog (Rv2623) are important in M. tuberculosis virulence and chronic infection, suggesting that Usps are important stress proteins across diverse bacterial species. We propose that UspA616 is a metabolic switch that controls survival by regulating the glyoxylate shunt. IMPORTANCE Bacteria tolerate severe external stresses, including antibiotics, through a nonreplicative persistent (NRP) survival state, yet the proteins regulating this survival state are largely unknown. We show a specific universal stress protein (UspA616) controls the NRP state in Micrococcus luteus. Usps are widely conserved across bacteria, but their biological function(s) has remained elusive. UspA616 inactivation renders M. luteus susceptible to stress: bacteria die instead of adapting through the NRP state. UspA616 regulates malate synthase and isocitrate lyase, glyoxylate pathway enzymes important for chronic Mycobacterium tuberculosis infection. These data show that UspA616 regulates NRP stress survival in M. luteus and suggest a function for homologous proteins in other bacteria. Importantly, inhibitors of UspA616 and homologs may render NRP bacteria more susceptible to stresses, including current antibiotics.