Question

1. The food industry must always be vigilant for bacteria that can survive the methods they try to use to keep the food safe. Let’s explore that a little in this question.

   1. There’s always danger from psychrophiles or facultative psychrophiles. How have these bacteria adapted to survive in their environment?

   2. Bacteria tend to grow very slowly in the refrigerator, but some can still grow there. Let’s say you just have one cell contaminating a food when you put it in the refrigerator, and it divides only once every 12 hours at 4oC. Let’s say it takes 1,000,000 of these bacteria to make a person sick (so less than that it’s still OK to eat). For how many days can you safely store this food in the refrigerator before you need to discard it?

   3. Endospores are notorious for being able to survive even in boiling water. How do they do this? Don’t just state the spore structure involved, explain in some detail how this structure allows survival. How is this structure produced during spore development?

Answer 1

A. Have you heard about what bacteria's love? lets explore more about it through this answer. Bacteria are classified under various conditions but let us restrict our discussion here only about the classification based on temperature. So the bacteria are classified as Psychrophiles which grow best at low temperatures, mesophiles grow at moderate temperature, Thermophiles grow best from optimum to maximum temperature. Amongst these let us make a clear understanding that psychrophiles are cold loving microbes. and what about Facultative microbes? the word Facultative means occuring optimally in response to circumstances rather than by nature. Therefore, Facultative psychrophiles can survive at low temperature and also at temperature of approx 40 degree celcius. These bacteria adapt to their environment by

1. They overcome the stiffening of their lipid cell membrane by adapting lipid membrane structures that have a high content of short and unsaturated fatty acids which makes the cell membranes have a low melting point and increase the fluidity of the membranes.  

2. When the temperatures drops the ice formation begins to occur in the cells. To avoid these psychrophiles produce antifreeze proteins that avoid ice formation.

B. Bacteria reproduce by binary fission where a single cells divides and gives rise to 2 identical daughter cells. if a cell divides only once in 12 hr then for 24hrs it divides twice. where No is the initial number of cells and "n" is number of generations. from the given data we know that No is 1 and Nt is 1,000000. Therfore we have,

100000 = 2ⁿ

Taking log on both sides,

log ( 1000000) = n log 2

6 = n(0.30)

n= 20, the number of generations for 24hrs is 2 therefore it takes 10 days for 1000000 bacteria to grow. Therefore it is recommended to safely store this food in refrigerator for less than 9 days.

C. Endospore is a non-reproductive structure produced by bacteria. Formation of these are usually triggered by stress conditions. like lack of nutrients. An endospore has an outer proteinaceous coat, beneath the coat there is a very thick layer of specialized peptidoglycan called cortex. This cortex is needed for dehydration of spore core which aids in resistance to high temperature.