Project description:Aspergillus oryzae is used in solid-state fermentation (SSF) to produce plant-based foods. To this end, the substrate is inoculated with spores of this fungus. So far, the effect of inoculum size on SSF with A. oryzae has primarily focused on the production of specific enzymes. Therefore, the aim of this study was to examine the impact of inoculum size on the full secretome, combined with enzyme activity assays, assessment of colonization, substrate degradation, and sporulation. To this end, A. oryzae was grown for 7 days on whole yellow pea (Pisum sativum). Fluorescence microscopy with a GFP-expressing A. oryzae strain showed that peas had been colonized externally and internally, irrespective of inoculum size. Yet, the highest inoculum size resulted in a stronger pea biomass reduction when compared to the lowest inoculum size. By contrast, sporulation decreased with increasing inoculum size. Notably, proteomics revealed no effect of inoculum size on the protein profiles of aqueous extracts of the colonized peas. Amylases and proteases were the most abundant secreted proteins, which was consistent with their high activity in the aqueous extracts. Proteomics also identified β-1,3-glucanases and chitinases, indicating hyphal lysis. Indeed, 10–19% of the fungal proteins detected in the aqueous extracts lacked signal peptides. These data contribute to our understanding of colonization of substrates by A. oryzae and may be used to optimize SSF with this food grade fungus.
Project description:Tan2012 - Antibiotic Treatment, Inoculum Effect
The efficacy of many antibiotics decreases with increasing bacterial density, a phenomenon called the ‘inoculum effect’ (IE). This study reveals that, for ribosome-targeting antibiotics, IE is due to bistable inhibition of bacterial growth, which reduces the efficacy of certain treatment frequencies.
This model is described in the article:
The inoculum effect and band-pass bacterial response to periodic antibiotic treatment.
Tan C, Phillip Smith R, Srimani JK, Riccione KA, Prasada S, Kuehn M, You L.
Mol Syst Biol. 2012 Oct 9; 8:617
Abstract:
The inoculum effect (IE) refers to the decreasing efficacy of an antibiotic with increasing bacterial density. It represents a unique strategy of antibiotic tolerance and it can complicate design of effective antibiotic treatment of bacterial infections. To gain insight into this phenomenon, we have analyzed responses of a lab strain of Escherichia coli to antibiotics that target the ribosome. We show that the IE can be explained by bistable inhibition of bacterial growth. A critical requirement for this bistability is sufficiently fast degradation of ribosomes, which can result from antibiotic-induced heat-shock response. Furthermore, antibiotics that elicit the IE can lead to 'band-pass' response of bacterial growth to periodic antibiotic treatment: the treatment efficacy drastically diminishes at intermediate frequencies of treatment. Our proposed mechanism for the IE may be generally applicable to other bacterial species treated with antibiotics targeting the ribosomes.
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