grow well in freezing environments. Freeze-drying is a way of storing these organisms for an extended period of time. This is referred to as lyophilization. Thermophiles and hyperthermophiles have differences in their chemical environment. They have more cytosine-guanine base pairs, which are more stable. There are high amounts of saturated lipids to decrease the membrane fluidity. There are proteins that are resistant to denaturation called thermoenzymes. Microbes have rigid cell walls in order to protect them from dilute environments. This prevents cells from bursting under conditions of low osmotic pressure. There are halophiles that live in high-salt environments, usually seen in marine environments or in even higher salt environments like the Great Salt Lake and the Dead Sea. Salt is often pumped actively out of the organism. There are also halotolerant organisms that will survive in high salt environments but do not require such environments. Barophiles are organisms that survive the high-pressure environments of the bottom of the ocean. These are difficult to grow outside of these environments so they are not well studied. As already talked about, organisms differ in their need for light. Some will be photoautotrophs, while others will be photoheterotrophs.
MEDIA AND MICROBIAL GROWTH Organisms are best studied when they can be grown and cultured in a medium. There are several types of media you will come across. Tryptic soy broth or TSB is commonly used. There are media that are particularly enriched with things like vitamins and growth factors for fastidious organisms that do not grow easily in regular media. Chemically defined media have exact concentrations of certain chemicals. Complex media has extracts of meat, plants, or yeasts that are less precisely put together. Selective media will grow certain organisms but not others. Enrichment cultures are selective media that will grow certain organisms that are low in number to the exclusion of other organisms.
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