Candida albicans reads one word of the genetic code differently from nearly all life
In almost every organism, the DNA triplet CUG tells the cell to add the amino acid leucine to a protein. In the common yeast Candida albicans it means serine instead. That quirk may keep the fungus in a constant state of stress readiness, and it lives quietly in the mouth or gut of roughly half of healthy adults.
Usually the yeast is a harmless resident, detected in the digestive tract and mouth of 40 to 60 percent of healthy adults. Trouble begins when it overgrows, typically in people with weakened immune systems such as those with HIV, causing the infection candidiasis, better known as thrush. Hippocrates described oral thrush around 400 BC. When the fungus invades the bloodstream, reported death rates reach 40 percent, and hospital-acquired invasive candidiasis kills an estimated 2,800 to 11,200 Americans a year. It is also the fungus most often found in biofilms coating implanted medical devices.
Its name is oddly repetitive. Candida comes from the Latin for shining white, and albicans means becoming white, so the whole phrase can be read as pure white becoming white. More than a hundred other names have been applied to the species over time.
The fungus is a shape-shifter. Often called dimorphic, it actually takes many forms: rounded yeast cells 10 to 12 microns across, long filaments, and several other states. Small shifts in temperature, carbon dioxide, nutrients or acidity can trigger the switch to filaments, which invade tissue and may help it escape immune cells, while yeast cells seem better suited to spreading through the blood. One laboratory strain spontaneously produces at least seven different colony types, reversibly, and passes them to offspring.
Its genome was one of the first fungal genomes fully sequenced, about 16 million DNA letters in the single-copy version, arranged as eight chromosome pairs with 6,198 potential genes, 70 percent of them still uncharacterised. Long thought to exist only with two chromosome sets, it turns out to have one-set and four-set stages as well. The unusual CUG reading complicates studying its proteins in ordinary brewer's yeast, so scientists built a dedicated test system for it.
Source: Candida albicans
