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1.25: Gelatin Hydrolysis

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    Learning Objectives
    • Explain what gelatin is and what gelatin hydrolysis is.
    • Tell that species that can hydrolyze gelatin have a gelatinase gene and produce a gelatinase enzyme.
    • Explain how the gelatin hydrolysis test works.
    • Successfully conduct and interpret the gelatin hydrolysis test.
    • Tell that gelatin hydrolysis is useful for characterizing and identifying bacterial species.


    Gelatin & Gelatin Hydrolysis

    Gelatin is a protein derived from collagen, a connective tissue of animals. When chilled on ice, gelatin forms cross-links to itself to create a semi-solid state (gelatin makes Jello! have its unique form and texture). Gelatin provides a rich source of amino acids and peptides for bacteria, but its structure is too large to be transported inside the cell directly. Therefore, it must first be broken down (gelatin hydrolysis) by exoenzyme proteins called gelatinases. Not all species of bacteria have a gene for a gelatinase enzyme. Only those species of bacteria that do have a gelatinase gene are capable of producing a gelatinase and are capable of breaking down gelatin and using it as a nutrient source. As such, the gelatin hydrolysis test is used to differentiate between bacteria that do and do not hydrolyze gelatin, and therefore is useful for characterizing and identifying bacterial species.

    To determine if a bacterial species hydrolyzes gelatin (and therefore has the a gelatinase gene and produces a gelatinase enzyme), the gelatin hydrolysis test is used. When bacteria that have this enzyme are inoculated into a nutrient medium containing gelatin, they will produce a gelatinase enzyme and break down the gelatin. After incubation of the bacteria in the medium that hydrolyze gelatin, the medium will no longer form a semi-solid state, even after chilling. Those species that do not hydrolyze gelatin will not have an effect on the gelatin and it will maintain its semi-solid state after chilling.


    gelatin hydrolysis test showing gelatin hydrolysis positive results and gelatin hydrolysis negative results

    Figure 1: Results from two gelatin hydrolysis tests. The top test tube shows a gelatin medium after chilling that has a more liquid form indicating that gelatin hydrolysis occurred (gelatin hydrolysis positive). The bottom test tube shows a gelatin medium after chilling that has a semi-solid state indicating that gelatin hydrolysis did not occur (gelatin hydrolysis negative).


    Laboratory Instructions

    1. For each bacterial species being tested, use aseptic technique to collect the bacteria using an inoculation needle and stab the gelatin deep with a needle all the way to the bottom (being careful NOT to get the metal holder into the agar).
    2. Incubate at 25º C for a couple days, up to a week. Keep the medium for a week if negative.
    3. Examine results by placing the test tubes on ice for 15 minutes or in the fridge for 30 minutes.


    Results & Questions


    Bacterial Species Gelatin medium liquid after incubation and chilling (+/-)

    Species hydrolyzes gelatin (+/-)

    Species has a gelatinase enzyme (+/-) Species has a gelatinase gene (+/-)
    1. Complete the table above with experimental results and interpretations.
    2. Why is it that when gelatin is broken down the gelatin medium no longer forms a semi-solid even after chilling?
    3. What is gelatin?
    4. Why might the ability to hydrolyze gelatin be an advantage for some species of bacteria?
    5. Why might gelatin hydrolysis be associated with pathogenic species and not non-pathogenic species?



    This page titled 1.25: Gelatin Hydrolysis is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Rosanna Hartline.

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