Lesson 5 - Types of microorganisms SAQ
This lesson enables you to test yourself on the material covered in the Types of Microorganisms lesson, and determine to what level you have attained the outcomes.
Suggested Response - Q2
**Answer BOTH parts of this question:
a) Give examples of Gram-positive beer spoiler bacteria and describe their impacts on beer quality.
b) Explain the systems they have developed to grow in hopped wort.
Response:
a) The Gram-positive beer spoilers are the lactic acid bacteria, genus Lactobacillus and Pediococcus. These bacteria produce turbidity and lactic acid, giving the beer a sour taste. Some species produce ropiness, which is seen as fine, silky strands in the beer, as well as other acids, such as acetic acid. Pediococcus is capable of producing diacetyl, giving beer an unwanted buttery flavour.
b) Gram-positive (G+) bacteria are susceptible to hop acids due to the makeup of their cell membrane. Some species of Lactobacillus and Pediococcus have developed resistance to the hop acids through a gene called hor A, which is carried on a plasmid in the cell. The hor A gene allows acidic H+ ions or protons that build up in the cell because of iso-α-acid mediated transport to be pumped out, preventing cell starvation and death.
Figure: Model of hop resistance in Gram-positive bacteria carrying the hor A gene