Biology subjects

Horn, S. J.

Publications and source records attributed to Horn, S. J..

3 recordsLinked to original sources

bioRxiv2026

Mild extraction preserves labile structural features of Gram-positive bacterial cell wall glycopolymers

Cell wall glycopolymers in Gram-positive bacteria are crucial for structural integrity, cell division, and stress resistance. Elucidating the structure of these glycopolymers is not only important for understanding fundamental bacterial physiology, but may facilitate vaccine development, phage therapy, antibiotic design and improvements in food fermentation safety. However, extraction protocols have so far relied on harsh chemicals that can damage these polymers, compromise their structural integrity, obscure their biological functions, and result in low yields. We present a straightforward method for isolating cell wall glycopolymers from Gram-positive bacteria that preserves essential structural features including attachment to peptidoglycan. The method was broadly applicable across phylogenetically diverse species and was not restricted to glycopolymer types. In total, we isolated 17 distinct glycopolymers from 11 species, including six with previously unreported structures, with a median yield of 49 mg per litre of culture. The simplicity and mild nature of the method, combined with the exceptional purity of the resulting products, has the potential to transform research on Gram-positive cell wall glycopolymers

microbiology↗

bioRxiv2026

High molecular-weight polysaccharide contamination from yeast extract in semi-defined bacteriological media: Effects on exopolysaccharide production and purity

Exopolysaccharides (EPS) produced by lactic acid bacteria (LAB) and other microorganisms have attracted considerable interest due to their structural diversity and physicochemical properties, which makes them valuable across various industrial applications. To achieve high cell densities and maximize EPS yields, microorganisms are typically cultivated in nutrient-rich media containing yeast extract. However, yeast extract may contain high molecular weight polysaccharides that are not metabolized by the bacteria. This can lead to an overestimation of EPS yields and contamination of the bacterial EPS, potentially resulting in misinterpretation of their structure and biological activity. In this study, we demonstrate the presence of high molecular weight -mannan and {beta}-glucan in yeast extract in EPS isolates using both ultrafiltration and the commonly used trichloroacetic acid/ethanol (TCA/EtOH) precipitation method. These polysaccharides were characterized by size-exclusion chromatography, high-performance anion-exchange chromatography, and nuclear magnetic resonance spectroscopy. Their abundances were estimated to range from 10 to 50 mg/L in MRS medium, depending on the supplier of the yeast extract. The main contaminant identified was yeast -mannan. By cultivating L. rhamnosus GG (ATCC 53103) and L. pentosus KW1 and isolating their respective EPS, we illustrate how these yeast extract contaminants affect the structural interpretation of the EPS and that the contaminants can be completely removed by ultrafiltration of the growth medium prior to bacterial cultivation. In conclusion, we emphasize the necessity of stringent controls in the production and purification of microbial EPS, with particular attention to the chemical purity of medium constituents.

microbiology↗

bioRxiv2016

Fenton-type chemistry by a copper enzyme: molecular mechanism of polysaccharide oxidative cleavage

The discovery of Lytic Polysaccharide Monooxygenases (LPMOs) has been instrumental for the development of economically sustainable lignocellulose biorefineries. Despite the obvious importance of these exceptionally powerful redox enzymes, their mode of action remains enigmatic and their activity and stability under process conditions are hard to control. By using enzyme assays, mass spectrometry and experiments with labeled oxygen atoms, we show that H2O2, and not O2 as previously thought, is the co-substrate of LPMOs. By controlling H2O2 supply, stable reaction kinetics and high enzymatic rates are achieved, the LPMOs work under anaerobic conditions, and the need for adding stoichiometric amounts of reductants is alleviated. These results offer completely new perspectives regarding the mode of action of these unique mono-copper enzymes, the enzymatic conversion of biomass in Nature, and industrial biorefining.

biochemistry↗