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Title: The effect of temperature upon the growth and metabolism of Aeromonas hydrophila and Lactobacillus plantarum in pure and mixed culture
Author: Griffiths, Jonathan T. H.
ISNI:       0000 0001 3520 4503
Awarding Body: Oxford Brookes University
Current Institution: Oxford Brookes University
Date of Award: 1996
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The effects of temperature upon the growth and metabolism of pure and mixed populations of Aeromonas hydrophila and Lactobacillus p/an/Qrum were studied. Initially a medium was developed to provide unbiased support for both organisms. The effect of temperature upon lag phase, growth rate, and final population level between pure and mixed culture was investigated. Temperature effects were only found to be significant when comparing the final population levels of Lb. p/anlDrum between pure and mixed culture. The lactobacilli exhibited a bomofermentative to heterofermentative switch between pure and mixed culture. This was probably due to substrate competition from the aeromonad population in mixed culture The metabolism of Aer. hydrophi!a has not been well described in the literature, compared to that of the lactobacilli. Due to the simplicity of the growth medium it was possible to determine the substrates relatively easily, although quantification required amino acid analysis. It was found that the organism utilized amino acids as primary substrates, switching to available carbohydrate as the population moved from growth to stationary phase. The principal product was found to be urea. During the stationary phase of population development it was interesting to note that the pH of the medium increased to well above the starting point of around S.S. This was principally due to de-amination of the urea product. Growth temperature above recognized optimum (28°C) was found to affect the metabolic profile of this organism, leading to low final pH levels. 4 The pattern of temperature effect upon the metabolism of Lb. plantarum as expressed by growth yields showed a similar pattern to the final population levels. The ratio of lactate formed : dextrose utilized was reversed at the 100e point. Growth of Lb. plantarum was not detected at the soe point. A new third order polynomial model was developed to describe the tag phase of bacterial cultures across a temperature range. The new model was compared with two others from the literature. The new model was chosen based upon statistical results. The pattern exhibited by final population levels at the different temperatures showed • similar point of inflection to that expressed by the polynomiallag phase model. The growth rate was modeled with the Schoolfield model which was proven to be the closest estimate of the three models tested. The theory ofhomeoviscous adaptation was used to explain the behavior patterns observed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Microbial physiology; Mathematical modelling