Analysis of a continuous-culture technique for the selection of mutants tolerant to extreme environmental stress

Lane, Phil; Oliver, Stephen G.; Butler, Philip R.

doi:10.1002/(sici)1097-0290(19991120)65:4<397::aid-bit4>3.0.co;2-x

Cited by 20 publications

(16 citation statements)

References 29 publications

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“…An analysis of the possible steady outcomes of competition between mutants in BOICS was presented by Lane et al (1999) and applies also to MBOICS. When the specific growth rate of the mutants can be considered to depend only on the inhibitor concentration, this analysis leads to the following main conclusions…”

Section: Resultsmentioning

confidence: 99%

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Selection of Microbial Mutants Tolerant To Extreme Environmental Stress Using Continuous Culture-Control Design

et al. 1999

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The design of controllers for a continuous selection technique (BOICS; Brown and Oliver, 1982) is considered. This technique is used to obtain microbial mutants that are tolerant to extreme environmental stress. Applications of BOICS have been hampered by the problem of controller design. In this paper, a modified implementation of BOICS is considered which has a number of practical advantages. A model-based approach to controller design is taken. The case in which the stress is due to an inhibitory substance in the growth environment is considered. The analysis is intended to be applicable to any reasonable combination of organism and inhibitor. Conventional linear and time-invariant controllers are considered. Guidelines for the selection of controller parameters' values are suggested. The application of these guidelines requires that certain process parameters' values be identified. Methods by which these parameters' values can be identified are suggested. Simulation results indicate that the resulting controllers perform satisfactorily. This is confirmed by experimental data from a model selection experiment. A recipe for the design of controllers is a necessary part of a protocol for BOICS. It is hoped that the solution to the controller design problem that is offered in this paper will encourage further applications for the technique.

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Section: Resultsmentioning

confidence: 99%

“…In this paper, a model‐based approach to controller design is taken. This is facilitated by an earlier analysis of Brown and Oliver's selection technique (Lane et al, 1999). That analysis provides an improved understanding of the process to be controlled and clarifies the control objectives.…”

Section: Introductionmentioning

confidence: 99%

Selection of Microbial Mutants Tolerant To Extreme Environmental Stress Using Continuous Culture-Control Design

et al. 1999

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“…As a comparison, batch cultures with free cells of B. longum NCC2705 generally reach 10 9 CFU ml -1 , corresponding to 10 12 CFU per litre of reactor at the end of the culture (data not shown). This high cell density could favor the occurrence of mutations since the rate of appearance of mutational events is proportional to the amount of biomass in the culture [27]. …”

Section: Discussionmentioning

confidence: 99%

New method for selection of hydrogen peroxide adapted bifidobacteria cells using continuous culture and immobilized cell technology

Mozzetti¹,

Grattepanche²,

Moine

et al. 2010

Microb Cell Fact

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BackgroundOxidative stress can severely compromise viability of bifidobacteria. Exposure of Bifidobacterium cells to oxygen causes accumulation of reactive oxygen species, mainly hydrogen peroxide, leading to cell death. In this study, we tested the suitability of continuous culture under increasing selective pressure combined with immobilized cell technology for the selection of hydrogen peroxide adapted Bifidobacterium cells. Cells of B. longum NCC2705 were immobilized in gellan-xanthan gum gel beads and used to continuously ferment MRS medium containing increasing concentration of H2O2 from 0 to 130 ppm.ResultsAt the beginning of the culture, high cell density of 1013 CFU per litre of reactor was tested. The continuous culture gradually adapted to increasing H2O2 concentrations. However, after increasing the H2O2 concentration to 130 ppm the OD of the culture decreased to 0. Full wash out was prevented by the immobilization of the cells in gel matrix. Hence after stopping the stress, it was possible to re-grow the cells that survived the highest lethal dose of H2O2 and to select two adapted colonies (HPR1 and HPR2) after plating of the culture effluent. In contrast to HPR1, HPR2 showed stable characteristics over at least 70 generations and exhibited also higher tolerance to O2 than non adapted wild type cells. Preliminary characterization of HPR2 was carried out by global genome expression profile analysis. Two genes coding for a protein with unknown function and possessing trans-membrane domains and an ABC-type transporter protein were overexpressed in HPR2 cells compared to wild type cells.ConclusionsOur study showed that continuous culture with cell immobilization is a valid approach for selecting cells adapted to hydrogen peroxide. Elucidation of H2O2 adaptation mechanisms in HPR2 could be helpful to develop oxygen resistant bifidobacteria.

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“…Symbols: f, the mutant strain at an ORP of Ϫ190 mV; Ⅺ, the mutant strain at an ORP of Ϫ240 mV; •, the mutant strain at an ORP of Ϫ280 mV; E, the mutant strain at an ORP of Ϫ320 mV; OE, the parent strain with the optimal ORP regulation process (adapted from our previous publication [14] cated that, with 5% higher 1,3-PD production in flask fermentations, it is also possible to get a strain with increased 1,3-PD production in scale-up fermentations. The environmental-tolerance screening method has also been reported in continuous culture (chemostat) to select strains with desired traits (15,19,29). In continuous culture, the stains that were not diluted out by environment pressure showed a high level of tolerance for a specified environment.…”

Section: Discussionmentioning

confidence: 99%

Novel Redox Potential-Based Screening Strategy for Rapid Isolation of Klebsiella pneumoniae Mutants with Enhanced 1,3-Propanediol-Producing Capability

Zhang

et al. 2007

Appl Environ Microbiol

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This report describes a novel redox potential (oxidoreduction potential [ORP])-based screening strategy for the isolation of mutants of Klebsiella pneumoniae which have an increased ability to produce 1,3-propanediol (1,3-PD). This method can be described as follows: first, to determine an ORP range which is preferred for the wild-type strain to grow and to produce 1,3-PD; second, to subject a chemically mutagenized culture to a reduced ORP level which is deleterious for the wild-type strain. Colonies that showed high specific growth rates at deleterious ORP levels were selected, and their abilities to produce 1,3-PD were investigated. In an ORP-based screening experiment where the ORP was controlled at ؊280 mV, 4 out of 11 isolated strains were recognized as positive mutant strains. A mutant which is capable of producing higher concentrations of 1,3-PD was subjected to fed-batch fermentations for further characterization. Its preferred ORP level (؊280 mV) was significantly lower than that of its parent (؊190 mV). The highest 1,3-PD concentration of the mutant was 915 mmol liter ؊1 , which was 63.1% higher than that of the parent. Metabolic-flux analysis suggested that the intracellular reductive branch of the mutant was strengthened, which improved 1,3-PD biosynthesis. The procedure and results presented here provide a novel method of screening for strains with improved product formation.

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Analysis of a continuous-culture technique for the selection of mutants tolerant to extreme environmental stress

Cited by 20 publications

References 29 publications

Selection of Microbial Mutants Tolerant To Extreme Environmental Stress Using Continuous Culture-Control Design

Selection of Microbial Mutants Tolerant To Extreme Environmental Stress Using Continuous Culture-Control Design

New method for selection of hydrogen peroxide adapted bifidobacteria cells using continuous culture and immobilized cell technology

Novel Redox Potential-Based Screening Strategy for Rapid Isolation of Klebsiella pneumoniae Mutants with Enhanced 1,3-Propanediol-Producing Capability

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