Lecture 10 - Variations

Variations are any change in the characteristics of an offspring compared to its parent, usually due to a mutation. There can be either a temporary phenotypic change, or a permanent genotypic change.

Phenotypic
Phenotypic changes can easily be reverted. An example is a change in gene expression, without any change to the gene itself. Can be common to all individuals within a microorganism colony.

Morphological
Morphological changes include microscopic appearance changes, and can include the size and shape changes of bacteria over its growth phase. For instance, bacteria can look like long bacilli when in their log growth phase, but look like small coccobacilli when in their log death curve. Morphological changes can also be caused by different media; organisms are smaller in agar than in broth.

Cultural
Cultural changes include macroscopic changes. Serratia marcescens are pure white when grown at 37C but bright red when grown at 25C.

Physiological
E. coli will produce over 3000 enzymes of beta galactosidase, a lactase, in the presence of lactose. In the abscence of lactose, E. coli stops expressing the gene for beta galactosidase.

Genotypic Variations
A genetic variation is a permanent and spontaneous change in DNA, or a mutation. For example, sickle cell anemia is caused by a rare mutation that makes affected individuals less vulnerable to Malaria.

Natural mutations are due to mistakes in making DNA. The rate of mutations is increased by ionizing radiation such as X-rays and UV light. Most mutations are silent, but some are lethal and others beneficial.

Colonial and Morphological Mutations
Smooth: Smooth, round, and shiny (slime layer). Single cultural colonies.

Rough: Wrinkled, irregular edges, and dull (dry). Formed in Streptobacilli, like Bacillus subtilis.

Mucoid: Smooth, round, and mucoid. Single bacteria that are enclosed in a capsule. Normal for Klebsiella pneumoniae.

Resistance Mutations
Some mutations can cause a resistance to drugs and antibiotics. For instance, S. aureus used to be sensitive to Penicillin, but insufficient dosages caused a resistant strain of the bacteria to grow.