Microbial lag phase can be indicative of, or independent from, cellular stress

Philip G Hamill,Kath E Stevenson,John E Hallsworth,Keith D Farnsworth,James P Williams,Andrew Stevenson,Phillip E Mcmullan,Galina Khroustalyova,Jon Y Takemoto,John P Quinn,Sudharsan S,Alexander Rapoport,Abiann D R Lewis

doi:10.1038/s41598-020-62552-4

Philip G Hamill, Kath E Stevenson + Show 11 more

Open Access

https://doi.org/10.1038/s41598-020-62552-4

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Abstract

Measures of microbial growth, used as indicators of cellular stress, are sometimes quantified at a single time-point. In reality, these measurements are compound representations of length of lag, exponential growth-rate, and other factors. Here, we investigate whether length of lag phase can act as a proxy for stress, using a number of model systems (Aspergillus penicillioides; Bacillus subtilis; Escherichia coli; Eurotium amstelodami, E. echinulatum, E. halophilicum, and E. repens; Mrakia frigida; Saccharomyces cerevisiae; Xerochrysium xerophilum; Xeromyces bisporus) exposed to mechanistically distinct types of cellular stress including low water activity, other solute-induced stresses, and dehydration-rehydration cycles. Lag phase was neither proportional to germination rate for X. bisporus (FRR3443) in glycerol-supplemented media (r2 = 0.012), nor to exponential growth-rates for other microbes. In some cases, growth-rates varied greatly with stressor concentration even when lag remained constant. By contrast, there were strong correlations for B. subtilis in media supplemented with polyethylene-glycol 6000 or 600 (r2 = 0.925 and 0.961), and for other microbial species. We also analysed data from independent studies of food-spoilage fungi under glycerol stress (Aspergillus aculeatinus and A. sclerotiicarbonarius); mesophilic/psychrotolerant bacteria under diverse, solute-induced stresses (Brochothrix thermosphacta, Enterococcus faecalis, Pseudomonas fluorescens, Salmonella typhimurium, Staphylococcus aureus); and fungal enzymes under acid-stress (Terfezia claveryi lipoxygenase and Agaricus bisporus tyrosinase). These datasets also exhibited diversity, with some strong- and moderate correlations between length of lag and exponential growth-rates; and sometimes none. In conclusion, lag phase is not a reliable measure of stress because length of lag and growth-rate inhibition are sometimes highly correlated, and sometimes not at all.

Highlights

Measures of microbial growth, used as indicators of cellular stress, are sometimes quantified at a single time-point
Chemical reactions and thermodynamic and biological processes often experience a lag period prior to reaching their maximum rate. This phenomenon that can be observed at various levels; thermodynamic processes
The specific aims of the current study were to: (i) determine windows of tolerance to solute- and water-induced stresses; (ii) determine whether there is a relationship between length of lag phase and exponential growth rates under these stresses for diverse model microbes; and (iii) consider the implications for studies of microbial stress biology

Summary

Introduction

Measures of microbial growth, used as indicators of cellular stress, are sometimes quantified at a single time-point. In reality, these measurements are compound representations of length of lag, exponential growth-rate, and other factors. A. sclerotiicarbonarius); mesophilic/psychrotolerant bacteria under diverse, solute-induced stresses (Brochothrix thermosphacta, Enterococcus faecalis, Pseudomonas fluorescens, Salmonella typhimurium, Staphylococcus aureus); and fungal enzymes under acid-stress (Terfezia claveryi lipoxygenase and Agaricus bisporus tyrosinase). These datasets exhibited diversity, with some strong- and moderate correlations between length of lag and exponential growth-rates; and sometimes none. This phenomenon that can be observed at various levels; thermodynamic processes

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