Oxygen availability and growth of Escherichia coli W3110: Dynamic responses to limitation and starvation

Abstract

It is well known that oxygen availability can have a profound effect upon the growth of an Escherichia coli culture with respect to acetate excretion or lower product yield. The current investigation seeks to determine the dynamic responses of steady state continuous cultures to abrupt changes in the oxygen supply. This should yield information regarding the behaviour of such cells as they circulate through areas of low and high oxygen availability in an industrial-scale bioreactor. It was found that a decoupling of catabolism and anabolism occurred following sudden switches both from and to oxygen limitation. It also appeared that the imposed growth rate had an effect on the speed of recovery of the system following any such changes. List of symbolsVolume of bioreactor (l) xBiomass concentration (g/l) x i Biomass concentration¯owing into bioreactor (g/l) x 0 Initial biomass concentration at commencement of new growth phase (g/l) l Substrate based biomass speci®c growth rate (h )1 ) l à Maximum speci®c biomass growth rate during non-steady state transition periods (h )1 ) l max Maximum speci®c biomass growth rate (h )1 ) IntroductionThe question of the effects of varying oxygen availabilities on the growth of Escherichia coli W3110 in batch culture was examined previously by O'Beirne and Hamer [1]. The objective of these experiments was to establish base-case data concerning the response of E. coli W3110 to constant preset operating parameters in an intensely agitated laboratory-scale bioreactor where perfect mixing could be assumed to be approached. Two series of experiments were conducted. The ®rst involved batch cultures growing on glucose which were subjected to a series of different ®xed sparged air¯ow rates; the second involved similar cultures which were subjected to constant sparged gas¯ow rates, each containing different volumetric oxygen concentrations. However, such results only represent a series of snapshots, rather than an overall picture of the dynamic responses that result from continuously changing oxygen availabilities, as occurs in large industrial-scale bioreactors.Transient responses of faculatively anaerobic bacteria to certain changes in their aeration status in well mixed laboratory-scale bioreactors have been investigated by Harrison and Loveless [2,3] with glucose grown cultures of both E. coli and Klebsiella aerogenes. They demonstrated reduced biomass yield coef®cients and corresponding increases in oxygen uptake rates, without extra cellular product (acetate) formation at low, but not limiting, dissolved oxygen concentrations [2] and that during transition from anaerobic to aerobic growth conditions, both the oxygen and the glucose based biomass yield coef®cients were depressed relative to those for steady state aerobic growth. However, such experiments neither sought to examine nor examined the types of changes and the dynamic responses thereto that occur in aerated cultures of faculative anaerobes subjected to either nutrient (oxygen) or substrate (glucose)¯uctuations. In fact one o...

Understanding the bioreactor

“…Step-change experiments in one reactor can be used to study dynamic effects of a sudden increase in glucose concentration or aerobic/anaerobic transitions [38,39]. A very rapid mixing of glucose can be obtained in a small STR.…”

Oxygen availability and the growth of Escherichia coli W3110: A problem exacerbated by scale-up

“…In spite of this shortcoming, the results obtained can be used to suggest what situations might be experienced by cells present at speci®c locations in a large-scale bioreactor. The more real case of the dynamic responses to¯uctuations in oxygen supply has been dealt with elsewhere [33]. Largescale fermentations [7] have shown that the dissolved oxygen concentration in a vessel¯uctuates with respect to time and increases appreciably at greater depths in the vessel as a result of hydrostatic pressure.…”

“…In reality individual cells are exposed tō uctuations in oxygen availability, which is why it is essential that measurements of the dynamic responses of cells to oxygen supply should be examined in order to achieve a deeper understanding. This topic is further developed by O'Beirne and Hamer [33].…”

Optimized Dissolved Oxygen Fuzzy Control for Recombinant Escherichia coli Cultivations

“…DOC was monitored by a dissolved oxygen sensor (8) (Mettler Inpro 6800-Columbus, OH, USA) and controlled by a hybrid system composed by a PID controller and a fuzzy controller. The PID controller set agitation speed between 200 and 950 rpm (9). Gas flow rate was controlled by two flowmeters (10) (GFC AALBORG-Orangeburg, NY, USA).…”

“…At first, high oxygen availability can lead to a high biomass yield, with low acetate production. However, at a certain point, oxygen surplus becomes detrimental for the cultivation (decreasing both biomass yield and specific growth rate and increasing acetate production) [9][10][11]. Given the low solubility of oxygen in water and mechanical stirring limitations of the bioreactor (limited agitation speed to avoid shearing and limited oxygen delivered by the gas sparge), the dissolved oxygen control is highly nonlinear and represents a challenging control problem [12,13].…”