Acies Bio (Slovenia)

ABSTRACTSmall‐conductance mechanosensitive channels (MscS) are established l‐glutamate exporters in industrially relevant bacteria, yet their role in the methylotrophic bacterium Bacillus methanolicus, a promising platform for sustainable methanol‐based l‐glutamate production, remains unexplored. Our research on B. methanolicus MGA3 identifies its MscS as the sole mechanosensitive channel in this organism and a key exporter of the amino acid l‐glutamate, providing valuable insights into its potential for industrial applications. Transcriptomic analysis of B. methanolicus wild type cultured on an l‐glutamate production medium revealed downregulation of the fatty acid biosynthesis genes fadR, fadF, mutB2, and acdA, suggesting that fatty acid metabolism is influenced by l‐glutamate overproduction, with consequent changes in membrane fluidity likely driving mechanosensitive channel‐mediated l‐glutamate efflux. The MscS‐like channel in B. methanolicus shares structural and functional similarities with MscS in Escherichia coli and with MscCG in Corynebacterium glutamicum. In silico structural predictions show that MGA3 MscS forms a homoheptameric structure with a transmembrane TM‐barrel, resembling that of E. coli MscS. The opening mechanism of the channel, driven by membrane dynamics, involves coordinated rotation and flipping of its transmembrane helices, with variations in lipid composition potentially influencing the channel's activity. Additionally, under biotin‐replete conditions, where this essential coenzyme supports carboxylases involved in fatty acid biosynthesis, l‐glutamate overproduction was suppressed in MGA3. Finally, metabolic engineering experiments inducing MscS gain‐ and loss‐of‐function further confirmed the channel's critical role in B. methanolicus amino acid production, proportionally enhancing and reducing l‐glutamate efflux, respectively. These findings open doors to novel strategies for engineering B. methanolicus and related methylotrophic organisms for sustainable amino acid production.

Abstract Yarrowia lipolyticais an oleaginous yeast with ever growing popularity in the metabolic engineering circles. It is well known for its ability to accommodate a high carbon flux through acetyl-CoA and is being extensively studied for production of chemicals derived from it.We investigated the effects of modifying the upstream metabolism leading to acetyl-CoA on beta-carotene production, including its titer, yield, and content. We examined the pyruvate and the phosphoketolase bypass, both of which are stoichiometrically favorable for the production of acetyl-CoA and beta-carotene. Additionally, we examined a set of genes involved in the carnitine shuttle. We constructed a set of parental strains derived from theY. lipolyticaYB-392 wild-type strain, each with a different capacity for beta-carotene production, and introduced genes for the metabolic bypasses in each of the constructed parental strains. Subsequently, we subjected these constructed strains to a series of fermentation experiments.We discovered that altering the upstream metabolism in most cases led to a decrease in performance for production of beta-carotene. Most notably, a set of genes used for the pyruvate bypass (YlPDC2,YlALD5, andYlACS1) and the phosphoketolase bypass (LmXPKandCkPTA) resulted in the reduction of more than 30%.Our findings contribute to our understanding ofY. lipolytica’s metabolic capacity and suggest that production of beta-carotene is most likely not limited solely by the acetyl-CoA supply. We also highlight a complex nature of engineeringY. lipolytica, as most of the results from studies using a different strain background did not align with our findings.

BackgroundNatural products are a valuable source of biologically active compounds that have applications in medicine and agriculture. One disadvantage with natural products is the slow, time-consuming strain improvement regimes that are necessary to ensure sufficient quantities of target compounds for commercial production. Although great efforts have been invested in strain selection methods, many of these technologies have not been improved in decades, which might pose a serious threat to the economic and industrial viability of such important bioprocesses.ResultsIn recent years, introduction of extra copies of an entire biosynthetic pathway that encodes a target product in a single microbial host has become a technically feasible approach. However, this often results in minor to moderate increases in target titers. Strain stability and process reproducibility are the other critical factors in the industrial setting. Industrial Streptomyces rimosus strains for production of oxytetracycline are one of the most economically efficient strains ever developed, and thus these represent a very good industrial case. To evaluate the applicability of amplification of an entire gene cluster in a single host strain, we developed and evaluated various gene tools to introduce multiple copies of the entire oxytetracycline gene cluster into three different Streptomyces rimosus strains: wild-type, and medium and high oxytetracycline-producing strains. We evaluated the production levels of these engineered S. rimosus strains with extra copies of the oxytetracycline gene cluster and their stability, and the oxytetracycline gene cluster expression profiles; we also identified the chromosomal integration sites.ConclusionsThis study shows that stable and reproducible increases in target secondary metabolite titers can be achieved in wild-type and in high oxytetracycline-producing strains, which always reflects the metabolic background of each independent S. rimosus strain. Although this approach is technically very demanding and requires systematic effort, when combined with modern strain selection methods, it might constitute a very valuable approach in industrial process development.

To combat the increasing spread of antimicrobial resistance and the shortage of novel anti-infectives, one strategy for the development of new antibiotics is to optimize known chemical scaffolds. Here, we focus on the biosynthetic engineering of Amycolatopsis sulphurea for derivatization of the atypical tetracycline chelocardin and its potent broad-spectrum derivative 2-carboxamido-2-deacetyl-chelocardin. Heterologous biosynthetic genes were introduced into this chelocardin producer to modify functional groups and generate new derivatives. We demonstrate cooperation of chelocardin polyketide synthase with tailoring enzymes involved in biosynthesis of oxytetracycline from Streptomyces rimosus. An interesting feature of chelocardin, compared with oxytetracycline, is the opposite stereochemistry of the C4 amino group. Genes involved in C4 transamination and N,N-dimethylation of oxytetracycline were heterologously expressed in an A. sulphurea mutant lacking C4-aminotransferase. Chelocardin derivatives with opposite stereochemistry of the C4 amino group, as N,N-dimethyl- epi-chelocardin and N,N-dimethyl-2-carboxamido-2-deacetyl- epi-chelocardin, were produced only when the aminotransferase from oxytetracycline was coexpressed with the N-methyltransferase OxyT. Surprisingly, OxyT exclusively accepted intermediates carrying an S-configured amino group at C4 in chelocardin. Applying medicinal chemistry approaches, several 2-carboxamido-2-deacetyl- epi-chelocardin derivatives modified at C4 were produced. Analysis of the antimicrobial activities of the modified compounds demonstrated that the primary amine in the R configuration is a crucial structural feature for activity of chelocardin. Unexpectedly, C10 glycosylated chelocardin analogues were identified, thus revealing the glycosylation potential of A. sulphurea. However, efficient glycosylation of the chelocardin backbone occurred only after engineering of a dimethylated amino group at the C4 position in the opposite S configuration, which suggests some evolutionary remains of chelocardin glycosylation.