The chemical composition of two stars in WLM have been determined from high quality UVES data obtained at the VLT UT2 1 . The model atmospheres analysis shows that they have the same metallicity, [Fe/H] = −0.38 ±0.20 (±0.29) 2 . Reliable magnesium abundances are determined from several lines of two ionization states in both stars resulting in [Mg/Fe] = −0.24 ±0.16 (±0.28). This result suggests that the [α(Mg)/Fe] ratio in WLM may be suppressed relative to solar abundances (also supported by differential abundances relative to similar stars in NGC 6822 and the SMC). The absolute Mg abundance, [Mg/H] = −0.62 is high relative to what is expected from the nebulae though, where two independent spectroscopic analyses of the H II regions in WLM yield [O/H] = −0.89. Intriguingly, the oxygen abundance determined from the O I λ6158 feature in one WLM star is [O/H] = −0.21 ±0.10 (±0.05), corresponding to five times higher than the nebular oxygen abundance. This is the first time that a significant difference between stellar and nebular oxygen abundances has been found, and presently, there is no simple explanation for this difference. The two stars are massive supergiants with distances that clearly place them in WLM. They are young (≤10 Myr) and should have a similar composition to the ISM. Additionally, differential abundances suggest that the O/Fe ratio in the WLM star is consistent with similar stars in NGC6822 and the SMC, galaxies where the average stellar oxygen abundances are in excellent agreement with the nebular results. If the stellar abundances reflect the true composition of WLM, then this galaxy lies well above the metallicity-luminosity relationship for dwarf irregular galaxies. It also suggests that WLM is more chemically evolved than currently interpreted from its color-magnitude diagram. The similarities between the stars in WLM and NGC6822 suggest that these two galaxies may have had similar star formation histories.1 Based on observations collected at the European Southern Observatory, proposal number 65.N-0375 2 In this paper, we adopt the standard notation [X/H] = log(X/H) -log(X/H) ⊙ . Also, abundances shall be reported with two uncertainties: the first is the line-to-line scatter, and the second (in parentheses and italics) is an estimate of the systematic error due to uncertainties in the atmospheric parameters.

Transcriptional and enzymatic analyses of Pyrococcus furiosus previously indicated that three proteins play key roles in the metabolism of elemental sulfur (S 0 ): a membrane-bound oxidoreductase complex (MBX), a cytoplasmic coenzyme A-dependent NADPH sulfur oxidoreductase (NSR), and sulfur-induced protein A (SipA). Deletion strains, referred to as MBX1, NSR1, and SIP1, respectively, have now been constructed by homologous recombination utilizing the uracil auxotrophic COM1 parent strain (⌬pyrF). The growth of all three mutants on maltose was comparable without S 0 , but in its presence, the growth of MBX1 was greatly impaired while the growth of NSR1 and SIP1 was largely unaffected. In the presence of S 0 , MBX1 produced little, if any, sulfide but much more acetate (per unit of protein) than the parent strain, demonstrating that MBX plays a critical role in S 0 reduction and energy conservation. In contrast, comparable amounts of sulfide and acetate were produced by NSR1 and the parent strain, indicating that NSR is not essential for energy conservation during S 0 reduction. Differences in transcriptional responses to S 0 in NSR1 suggest that two sulfide dehydrogenase isoenzymes provide a compensatory NADPH-dependent S 0 reduction system. Genes controlled by the S 0 -responsive regulator SurR were not as highly regulated in MBX1 and NSR1. SIP1 produced the same amount of acetate but more sulfide than the parent strain. That SipA is not essential for growth on S 0 indicates that it is not required for detoxification of metal sulfides, as previously suggested. A model is proposed for S 0 reduction by P. furiosus with roles for MBX and NSR in bioenergetics and for SipA in iron-sulfur metabolism.

The production of biofuels from lignocellulose yields a substantial lignin by-product stream that currently has few applications. Biological conversion of lignin-derived compounds into chemicals and fuels has the potential to improve the economics of lignocellulose-derived biofuels, but few microbes are able both to catabolize lignin-derived aromatic compounds and to generate valuable products. While Escherichia coli has been engineered to produce a variety of fuels and chemicals, it is incapable of catabolizing most aromatic compounds. Therefore, we engineered E. coli to catabolize protocatechuate, a common intermediate in lignin degradation, as the sole source of carbon and energy via heterologous expression of a nine-gene pathway from Pseudomonas putida KT2440. We next used experimental evolution to select for mutations that increased growth with protocatechuate more than 2-fold. Increasing the strength of a single ribosome binding site in the heterologous pathway was sufficient to recapitulate the increased growth. After optimization of the core pathway, we extended the pathway to enable catabolism of a second model compound, 4-hydroxybenzoate. These engineered strains will be useful platforms to discover, characterize, and optimize pathways for conversions of ligninderived aromatics.IMPORTANCE Lignin is a challenging substrate for microbial catabolism due to its polymeric and heterogeneous chemical structure. Therefore, engineering microbes for improved catabolism of lignin-derived aromatic compounds will require the assembly of an entire network of catabolic reactions, including pathways from genetically intractable strains. Constructing defined pathways for aromatic compound degradation in a model host would allow rapid identification, characterization, and optimization of novel pathways. We constructed and optimized one such pathway in E. coli to enable catabolism of a model aromatic compound, protocatechuate, and then extended the pathway to a related compound, 4-hydroxybenzoate. This optimized strain can now be used as the basis for the characterization of novel pathways.KEYWORDS lignin, protocatechuic acid, ortho-cleavage pathway, experimental evolution, synthetic biology, ligninolysis, metabolic engineering, ortho-cleavage B iofuels derived from lignocellulose will likely play an important role in the transition to a sustainable and carbon-neutral economy (1). In a typical biotransformation, carbohydrate-rich cellulose and hemicellulose are extracted and fermented to yield the desired biofuel, such as bioethanol. The lignin, comprising up to 25% of the dry

BackgroundAnthocyanins such as cyanidin 3-O-glucoside (C3G) have wide applications in industry as food colorants. Their current production heavily relies on extraction from plant tissues. Development of a sustainable method to produce anthocyanins is of considerable interest for industrial use. Previously, E. coli-based microbial production of anthocyanins has been investigated extensively. However, safety concerns on E. coli call for the adoption of a safe production host. In the present study, a GRAS bacterium, Corynebacterium glutamicum, was introduced as the host strain to synthesize C3G. We adopted stepwise metabolic engineering strategies to improve the production titer of C3G.ResultsAnthocyanidin synthase (ANS) from Petunia hybrida and 3-O-glucosyltransferase (3GT) from Arabidopsis thaliana were coexpressed in C. glutamicum ATCC 13032 to drive the conversion from catechin to C3G. Optimized expression of ANS and 3GT improved the C3G titer by 1- to 15-fold. Further process optimization and improvement of UDP-glucose availability led to ~ 40 mg/L C3G production, representing a > 100-fold titer increase compared to production in the un-engineered, un-optimized starting strain.ConclusionsFor the first time, we successfully achieved the production of the specialty anthocyanin C3G from the comparatively inexpensive flavonoid precursor catechin in C. glutamicum. This study opens up more possibility of C. glutamicum as a host microbe for the biosynthesis of useful and value-added natural compounds.Electronic supplementary materialThe online version of this article (10.1186/s12934-018-0990-z) contains supplementary material, which is available to authorized users.

Iron–sulfur clusters are ubiquitous in biology and function in electron transfer and catalysis. They are assembled from iron and cysteine sulfur on protein scaffolds. Iron is typically stored as iron oxyhydroxide, ferrihydrite, encapsulated in 12 nm shells of ferritin, which buffers cellular iron availability. Here we have characterized IssA, a protein that stores iron and sulfur as thioferrate, an inorganic anionic polymer previously unknown in biology. IssA forms nanoparticles reaching 300 nm in diameter and is the largest natural metalloprotein complex known. It is a member of a widely distributed protein family that includes nitrogenase maturation factors, NifB and NifX. IssA nanoparticles are visible by electron microscopy as electron-dense bodies in the cytoplasm. Purified nanoparticles appear to be generated from 20 nm units containing ∼6,400 Fe atoms and ∼170 IssA monomers. In support of roles in both iron–sulfur storage and cluster biosynthesis, IssA reconstitutes the [4Fe-4S] cluster in ferredoxin in vitro.