Conditional confined oscillatory dynamics of Escherichia coli strain K12-MG1655 in chemostat systems

Abstract

A series of continuous- and sequencing-batch reactor experiments were performed to assess the growth dynamics of Escherichia coli strain K12-MG1655 in chemostat systems. Previous mathematical predictions and early experimental results had shown that confined oscillatory dynamics ensue in bioreactor populations, which relates to "group birth and death" events within the population. New results are reported here that generally verify the predictions of the model and show that confined oscillations occur under different initial conditions, but the characteristics of the oscillatory dynamics vary as a function of the hydraulic retention time (HRT). Bioreactors were operated at HRTs ranging from 2.7 to 35 h and, regardless of initial conditions or the imposition of transient operational instabilities, highly patterned oscillations developed when HRT was between ∼3 and 8 h. However, outside of this range, bioreactor populations tended to form biofilms on the reactor walls (although the majority of the cells remained suspended in the bulk solution) and stable oscillations were not seen in the bulk phase. This suggests that alternate operating "states" might exist in chemostat populations with biofilm formation and non-homogenous spatial growth influencing "system" dynamics at very low and high HRTs. Although the model accurately predicts a confined dynamic equilibrium for mid-range HRT operations, experimental data show that model predictions do not extend outside of this range, when an alternate stable-state seems to be attained.

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 ).…”

Insights into the low-temperature adaptation and nutritional flexibility of a soil-persistentEscherichia coli

“…The nutritional adaptability of a reference laboratory strain, E. coli K12, was also determined for comparative purposes, and the cold‐adaptation response of both E. coli strains was investigated using proteomics. Escherichia coli K12 was not chosen as a representative isolate of enteric E. coli , but as a reference laboratory strain, which is still extensively characterized (McQuillan et al ., ; Prieto et al ., ; Freddolino et al ., ; Gohler et al ., ; Guillemet & Moreau, ; Liu et al ., ; Meier et al ., ; Ofiteru et al ., ; Pinske & Sawers, ; Rath et al ., ). This study tested the hypothesis that environmentally persistent E. coli leached from a temperate maritime soil possess a high nutritional versatility at low temperature, which could enhance their capacity to survive and become naturalized in the soil environment.…”

Redox controls metabolic robustness in the gas-fermenting acetogenClostridium autoethanogenum

“…Metabolic responses are generally fast, making it difficult to analyze their dynamics and understand the specific mechanisms underlying self-organization in a given species. However, some biological systems will spontaneously develop stable oscillations in continuous culture at high cell density (4)(5)(6)(7)(8)(9)(10)(11). These oscillating cultures offer an opportunity to understand fundamental principles of metabolic regulation and what limits metabolism.…”