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.
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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
