Non-linear population dynamics in chemostats associated with live–dead cell cycling in Escherichia coli strain K12-MG1655

Abstract

Bacterial populations conditionally display non-linear dynamic behaviour in bioreactors with steady inputs, which is often attributed to varying habitat conditions or shifting intracellular metabolic activity. However, mathematical modelling has predicted that such dynamics also might simply result from staggered birth, growth, and death events of groups of cells within the population, causing density oscillations and the cycling of live and dead cells within the system. To assess this prediction, laboratory experiments were performed on Escherichia coli strain K12-MG1655 grown in chemostats to first define fine-scale population dynamics over time (minutes) and then determine whether the dynamics correlate with live-dead cell cycles in the system. E. coli populations displayed consistent oscillatory behaviour in all experiments. However, close synchronisation between OD₆₀₀ and live-dead cell oscillations (within ~33-38 min cycles) only became statistically significant (p < 0.01) when pseudo-steady state operations approaching carrying capacity existed in the bioreactor. Specifically, live cells were highest at local OD₆₀₀ maxima and lowest at local OD₆₀₀ minima, showing that oscillations followed live-dead cell cycles as predicted by the model and also consistent with recent observations that death is non-stochastic in such populations. These data show that oscillatory dynamic behaviour is intrinsic in bioreactor populations, which has implications to process operations in biotechnology.

Heterogeneity in Pure Microbial Systems: Experimental Measurements and Modeling

“…A proposed way to overcome extrinsic heterogeneity and obtain similar performance in large scale reactors compared with laboratory reactors is to use strains specifically engineered to withstand certain environmental variability ( Löffler et al, 2016 ). However, some investigations, both by modeling ( Lavric and Graham, 2010 ) and experimental studies ( Chi Fru et al, 2011 ; Ofiţeru et al, 2012 ) suggest that bacterial populations display constant heterogeneity in apparently steady growth and habitat conditions, questioning the very existence of truly homogenous cultures ( Grote et al, 2015 ).…”

Recycling of Glass Waste by Deposition of TiO2 for the Intensification of the Photocatalytic Effect in the Purification of Wastewater

“…The results for the control sample reveal the presence of a long lag phase and a short exponential cell growth trend, which occurs in the first 100 mins, after which the effect of UV radiation on the concentration of the total number of cells decreases by 30%. The samples kept for viability testing demonstrated the reversible effect of UV action on cell development-the overall cells count variation curve-highlighting cell growth with lag and exponential growth phases but with a low slope (38%), compared with the normal growth of this strain [41].…”