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11.2: Introduction

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    Heat is a common method of controlling the growth of microorganisms. But what temperatures are sufficient? We can freeze, refrigerate, pasteurize, boil, autoclave, incinerate, etc. Why do we need so many different methods?

    Different bacteria flourish or survive at different temperatures. Some microbes live in glaciers, some in the guts of animals, others in hot springs. The range that a particular bacterium grows in is called the cardinal temperatures: the minimum, optimum, and maximum temperatures. Outside of that range the bacterium may not survive. Bacteria can be categorized based on their temperature requirements for optimal growth:

    • Psychrophiles: \(0^\circ C - 20^\circ C\)
    • Psychrotrophs: \(0^\circ C - 35^\circ C\)
    • Mesophiles: \(15^\circ C - 45^\circ C\)
    • Thermophiles: \(45^\circ C - 80^\circ C\)
    • Hyperthermophiles: \(65^\circ C - 113^\circ C\)
    Figure \(\PageIndex{1}\): This graph shows the cardinal temperatures range for a bacterium. The minimum temperature is 20 o C, the optimum is 32 o ,
    and the maximum is 45 0 C. We would characterize this bacterium as a Mesophile. Why? You will need to refer back to this graph when you work on the Questions section at the end of the lab.

    Temperature may have several different effects on the cell that can inhibit growth, decrease metabolic function, or cause cell death. Metabolic reactions and efficiency in a cell are dependent on enzymes, and on membrane activity and transport. Enzymes are proteins; therefore, they can be denatured by both high and low temperatures. Enzyme activity can be sped up by higher temperatures and slowed by lower temperatures. The optimal temperature is that which provides for efficient enzyme/metabolic activity within the cell. In addition, high temperatures can disrupt membranes and transport systems by destroying (“melting”) lipids in the membrane. Low temperatures can slow membrane transport and decrease (“solidify’) fluidity of the membrane. Microorganisms that live at the extremes have structural and metabolic adaptations that help them survive.

    In this exercise you will grow different bacteria at a range of temperatures to examine their growth patterns. You will observe the range and optimal temperature for each. In addition you will examine the effect of temperature on gene expression and metabolism by observing production of the pigment prodigiosin by Serrratia marcescens

    Contributors and Attributions

    This page titled 11.2: Introduction is shared under a CC BY license and was authored, remixed, and/or curated by Kelly C. Burke.

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