Biology subjects

Roder, H. L.

Publications and source records attributed to Roder, H. L..

5 recordsLinked to original sources

bioRxiv2026

Stressostat cultivation of Lactococcus lactis improves lactate stress resistance through mutations in RNA polymerase

Adaptive laboratory evolution is used to improve the phenotypes of microorganisms and to characterise the mechanisms underlying resistance against complex growth inhibition. Here we focused on lactic acid bacteria (LAB) as starter cultures for food fermentations. Production of LAB starter cultures is challenging due to growth inhibition by organic acids, mainly lactate, produced during fermentation. By utilising stressostat cultivation we generated Lactococcus lactis isolates with enhanced lactate resistance. Using a combination of (meta)genomics, proteomics and pH-controlled batch fermentations, we deciphered the lactate resistance mechanisms of these L. lactis isolates. Proteome responses of L. lactis, combined with similar growth inhibition at high salt, suggest that high lactate mainly causes osmotic stress. We identified RNA polymerase (RNAP) mutations in subunits {beta} (rpoB) and {beta} (rpoC) as key mutations, causing pleiotropic effects in the proteome. These proteome adaptations are linked to enhanced lactate resistance, particularly the resistance to hyperosmotic stress without glycine-betaine supplementation, likely by altering cross-linking of the peptidoglycan in the cell envelope via downregulation of MurE. The proteome changes indicate that lactate might (indirectly) cause oxidative stress. Combined, our study shows that RNAP mutations enhanced lactate resistance through pleotropic effects in the proteome that changed L. lactis responses against multiple stresses. HighlightsO_LILactate resistant variants were isolated from stressostat cultivations C_LIO_LIMetagenomics revealed evolutionary trajectory during stressostat cultivation C_LIO_LIRNAP mutations were identified as key drivers for improved lactate resistance C_LIO_LIRNAP mutations altered the proteome, enhancing the osmotic stress resistance C_LI

microbiology↗

bioRxiv2025

Matrix Matters: Context-Driven Metabolic Shifts in Bacillus cereus and Bacillus subtilis

Spore-forming Bacillus species, including pathogenic Bacillus cereus and spoilage-associated Bacillus subtilis, are major contributors to foodborne illness and product degradation. Understanding their metabolic behaviour in diverse food matrices is essential for improving risk assessment, spoilage prediction, and fermentation control. This study integrates isothermal microcalorimetry and targeted metabolomics to characterize the metabolic activity of B. cereus and B. subtilis in five nutrient sources: Brain Heart Infusion (BHI) medium, oat drink, milk, pea hydrolysate, and a combined oat-pea matrix. Metabolic heat production was monitored for 24 hours at 30{degrees}C. In BHI, B. cereus exhibited a shorter lag phase (mean {+/-} sd: 4.3 hours {+/-} 0.8) than B. subtilis (7.9 hours {+/-} 1.0) but produced less total heat. Across all food matrices, B. subtilis consistently generated more heat. The oat-pea matrix supported the highest calorimetric growth rates, surpassing oat or pea alone, and showed sugar depletion and accumulation of organic acids, indicating enhanced carbohydrate metabolism. Free amino acid release was matrix- and species-specific: B. subtilis had increased levels in oat, while B. cereus did so in pea. While B. cereus was metabolically active in all matrices, cereulide levels were matrix-dependent: 47.3 {+/-} 1.7 ng/mL in oat, 3.0 {+/-} 0.1 ng/mL in oat-pea, and undetectable in pea. These findings reveal clade-specific and matrix-driven metabolic strategies. This is the first study to combine calorimetry and metabolomics to evaluate Bacillus activity in plant-based and dairy matrices. This approach enhances our understanding of microbial physiology in complex food systems and provides a foundation for developing targeted strategies to improve food safety, stability, and product design.

microbiology↗

bioRxiv2025

A chemically defined medium to support the growth of food-relevant Bacillus species

The Bacillus genus contains many members with food significance, including the food-grade Bacillus subtilis clade often used in fermentations and the pathogenic Bacillus cereus clade. Chemically defined media for Bacillus species are crucial tools to allow detailed investigations of the influence of specific nutrients on growth and also improve reproducibility and consistency of experiments. Previous studies have focused on the development of defined media for single species, while the aim of this study was to develop a chemically defined medium that supports the growth of multiple food relevant Bacillus species. The new medium, Pafoba, was tested using two pathogenic strains of the Bacillus cereus clade and eleven strains of the Bacillus subtilis clade representing seven different clade members. All thirteen Bacillus strains were able to grow on Pafoba, of which ten displayed a similar or higher maximum OD600 on Pafoba medium compared to rich medium (Brain Heart Infusion broth). Detailed analysis revealed a biotin requirement for Bacillus subtilis strain PRO64, and the necessity of including essential amino acids for Bacillus weihenstephanensis and Bacillus cereus strains. In conclusion, the chemically defined Pafoba medium provides a controlled and reproducible growth environment for fundamental studies and is suitable for detection and enumeration of a broad range of Bacillus spp. related to food processing and safety. ImportanceBacillus species are important in both food fermentation and food safety. While members of the Bacillus subtilis clade are used in the production of fermented foods, those in the Bacillus cereus group are associated with foodborne illness. This study presents a chemically defined medium that supports the growth of multiple food-relevant Bacillus species, enabling precise control over nutrient composition. Knowledge of Bacillus cereus metabolism under defined conditions is essential to support efforts in food safety, risk assessment, and the development of targeted intervention strategies. Likewise, an understanding of Bacillus subtilis metabolism under defined conditions is essential to optimize fermentation processes, improve product consistency, and enhance functional food development. By providing a standardized and reproducible growth environment, the medium developed in this study will facilitate research that advances both microbial food safety and the controlled use of beneficial Bacillus strains in food production.

microbiology↗

bioRxiv2023

Evolution of genotypic and phenotypic diversity in multispecies biofilms

Bacterial fitness and adaptability in microbial communities are influenced by interspecies interactions and spatial organization. This study investigated how these factors shape the evolutionary dynamics of Bacillus thuringiensis. A distinct phenotypic variant of B. thuringiensis emerged consistently under both planktonic and biofilm conditions, as well as in monospecies and mixed-species settings, but was strongly selected in biofilms and during coexistence with Pseudomonas defluvii and/ or Pseudomonas brenneri. Compared to its ancestor, the variant exhibited shorter generation times, reduced sporulation, auto-aggregation, and lower biomass in mixed-species biofilms. Mutations in the spo0A regulator, which controls sporulation and biofilm matrix production, were identified in all variants. Proteomics revealed a reduction in TasA, a key matrix protein, in the variant but increased levels in co-culture with P. brenneri. These findings highlight how interspecies interactions drive B. thuringiensis diversification, promoting traits like reduced matrix production and species coexistence, with implications for microbial consortia applications in agriculture and biopesticides.

microbiology↗

bioRxiv2018

In vitro community synergy between bacterial soil isolates can be facilitated by pH stabilisation of the environment

Composition and development of naturally occurring microbial communities is defined by a complex interplay between the community and the surrounding environment and by interactions between community members. Intriguingly, these interactions can in some cases cause community synergies where the community is able to outperform it single species constituents. However, the underlying mechanisms driving community interactions are often unknown and difficult to identify due to high community complexity. Here we show how pH stabilisation of the environment through the metabolic activity of specific community members acts as a positive inter-species interaction driving in vitro community synergy in a model consortium of four co-isolated soil bacteria: Microbacterium oxydans, Xanthomonas retroflexus, Stenotrophomonas rhizophila and Paenibacillus amylolyticus. Using micro-sensor pH measurements to show how individual species change the local pH micro-environment, and how co-cultivation leads to a stabilised pH regime over time. Specifically, in vitro acid production from Paenibacillus amylolyticus and alkali production primarily from Xanthomonas retroflexus lead to an overall pH stabilisation of the local environment over time, which in turn resulted in enhanced community growth. This specific type of interspecies interaction was found to be highly dependent on media type and media concentration, however similar pH drift from the individual species could be observed across media variants.\n\nImportanceWe show that in vitro metabolic activity of individual members of a synthetic, co- isolated model community presenting community synergistic growth arises through the inter-species interaction of pH stabilization of the community micro-environment. The observed inter-species interaction is highly media specific and most pronounced under high nutrient availability. This adds to the growing diversity of identified community interactions leading to enhanced community growth.

microbiology↗