Biochemistry Questions / Discuss how phase variation allows bacteria to evade immune responses by changing the antigens they present. Provide examples of mechanisms used by bacteria for phase variation.

Phase variation is the stochastic control of gene expression, allowing random genes to be expressed, or silenced, without conscious control by the bacteria.

By randomly turning off genes, it is possible for a population of bacteria to express multiple phenotypes even in a clonal population. This variation may increase a bacteria’s survival chances, through random silencing of antigenic proteins or enzymes producing antigen molecules, allowing immune evasion.

Phase variation is normally done by epigenetic control of gene expression.