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Oxygen is a factor that affects microbial growth. Different bacteria require different amounts oxygen which we can test by growing bacteria in a thioglycolate tube cultures. This tube uses a autoclaves thioglycolate medium that have a low percentage of agar to allow for bacteria to move throughout it. Over time, oxygen diffuses and bacterial density increases in areas where the oxygen concentration is best for growth for that type of organism. Growth can be classified as: obligate aerobes (growth on top of the tube), obligate anaerobes (growth on the bottom of the tube), facultative anaerobes (heavy growth on top with growth throughout), aerotolerant anaerobes (indifferent to presence of oxygen), and microaerophiles (require the minimum amount of oxygen for growth). Microbes also have an optimum growth temperature that depends on the type of organism. Mesophiles are organisms that have adapted to temperatures ranging from 20 ºC to around 45 ºC. Psychotrophs survive in cooler temperatures; from 25 ºC to around 4 ºC. Thermophiles are heat loving and grow at temperatures ranging from 50 ºC to 80 ºC. Macromolecule differences can be seen when comparing thermophiles and hyperthermophiles to mesophiles. For example, their DNA has a higher zequence of guanine-cytosine bases. Microbes have optimal pH ranges as well. Most bacteria are neutrophiles and optimally grow within 1-2 units of neutral, or 7. Acidophiles grow optimally at a pH of less than 5.55 and alkaliphiles grow best between a pH of 8.0 and 10.5 (Parker et al., 2016). Need Assignment Help?