The effect of heat on growth and survival of bacteria.
Aims.
This experiment will analyse and discuss the effect of heat, on growth and survival on different species of bacteria. Potentially demonstrating individual niches, and diversity within the microbial world.
Results.
The effect of temperature on growth. (Table 1) bacteria Temperature °C 5 25 37 45 55
B. Stearothermorphilus 0 0 0 0 1
E. coli 0 2 3 3 0
E. Faecalis 0 2 2 1 0
Ps. Fluorescens 2 2 1 1 0
B. Subtilus 0 3 3 2 0
Growth key (degrees of growth) : 3=heavy growth, 2= medium growth, 1= slight growth, 0= no growth.
A number of conclusions can be drawn from the above results table, the majority of the bacteria seem to produce heavy growth around the mid-range of temperatures, however there are a couple of exceptions, Ps. Fluorescens produces considerable growth at 5°C which then declines as the temperature increases and B. Stearothermorphilus demonstrates only small growth at 55°C showing instantly a level of diversity amongst the species.
The effect of heat on survival of bacteria. (Table 2) Temperature °C
Bacteria control 40 60 80 100 2 minute 5 minute 30 minute 90 minute 2 minute 5 minute 30 minute 90 minute 2 minute 5 minute 30 minute 90 minute 2 minute 5 minute 30 minute 90 minute
B. Subtilus 1 + + + + + + + + + + + + + + + - - 2 + + + + + + + + + + + + + + + - -
E. coli 1 + + + + + + + + - - - - - - - - - 2 + + + + + + + + - - - - - - - - -
B. Stearothermorphilus 1 + + + + + + + + + + + + + + + - - 2 + + + + + + + + + + + + + - + - -
E. Faecalis 1 + + + + + + + + + + + - - - - - - 2 + + + + + + + + + + + - - - - - -
Ps. Fluorescens 1 + + + + + + + - - + + - - - - - - 2 + + + + + + + + - - - - - - - - - 3 + + + + + + + + + + + + - - - - - Graph key : minute = time spent in a water bath of each specific temperature. 1,2,3= the sample of that specific bacteria eg.1st, 2nd,3rd. += growth occurred, - = no growth
The above table demonstrates a range of different things, Firstly each species all survive up 40°C for 90 minutes and to 60°C for 5 minutes, with non-surviving at 100°C for longer than 5 minutes.
Secondly each repeat of techniques performed on a sample seem to show similarities between how long each organism can survive for at specific heat, for example both E. coli samples survived up to 60°C for 30 minutes, but provided no signs of survival after this. Alternatively Ps. Fluorescens three repeats show sporadic findings. B. Stearothermorphilus results demonstrated an anomaly in experiment 2, at 100°C, after 2 minutes no life was seen, however at 5 minutes there was evidence of life
Discussion.
Based on the results from the two different experiments, a range of findings can be drawn.
Firstly table 1; each bacterium grew differently from one and other. B. Stearothermorphilus, showed no sign of life until 55°C. Hotchkiss and Potter (1998) state that bacteria which grow at higher temperatures (50°C and higher) are referred to as a thermophile’s. E. coli, B. Subtilus and E. Faecalis, all appear to grow in the mid-range of table ones temperatures, Madigan and Martinko (2006) state that bacteria which grow in the common range of 20°C to 45°C are known as Mesophiles . Ps. Fluorescens in table one seems to demonstrate growth at very low temperatures, Hotchkiss and Potter (1998) state that bacteria able to grow at this temperature are known as Psychrophilic.
Within table two The 5 species of bacteria survived at 40°C up to 90 minutes, then survival is maintained until 5 minutes of heat exposure at 60 °C at this point E. coli dies, Madigan and Martinko (2006) state there is a maximum temperature for survival, beyond which viability decreases and death occurs, this suggests at 60°C the E. coli bacteria, protein’s denature and can no longer function biological processes. Also damaging the bacteria’s S-layer making it more susceptible to heat (Madigan and Martinko 2006). Within table two
