Candida albicans

Description and significance

Candida albicans is able to sexually reproduce and is a diploid fungus. It is often associated with yeast related diseases in the genitals and in the mouth of animals. It is one of the most common pathogens found in humans and is the source of a variety of different infections. Like most microorganisms found in the digestive tract of animals, C. albicans falls into a class of relationships that occur between organisms where one benefits and the other is not significantly harmed or benefited. C. albicans can be found in most of the general population causing no detrimental side effects. Although it is not found to be harmful, an overgrowth of C. albicans, known as candidasis, is harmful to the individual. Individuals with a healthy immune system are able to fight off the disease, however in HIV patients with weakened immune systems; it is much more difficult for the disease to be fought off and can lead to more serious problems. In order for the disease to be transmitted to the host, the yeast form of C. albicans responds to changes in the environment, becomes harmful, and changes from a unicellular form into a multicellular.

Genome

C. albicans was one of the first eukaryotic pathogens chosen for gene sequencing. The genome of Candida albicans was sequenced due to the fact that it is one of the most common human fungal pathogen. Most isolates of C. albicans used for genetic analysis are mostly diploid and some even contain translocations in their genes. Unlike most species that undergo sequencing, a haploid form of C. albicans is unavailable. Due to its extensive use in molecular analyses and virulence in animal models, SC5314(7) was selected for large- scale sequencing. C. albicans was first sequenced at the Stanford DNA Sequencing and Technology Center. The diploid sequence assembly displayed the amount of heterozygosity in the strain SC5314. The results obtained from this along with results from the sequencing afforded many important discoveries in C. albicans development.To put together the C. albicans diploid genome sequence, a commonly used assembly program called the “phrap” was used. Using the phrap, resulted in an assembly in which the products of the overlapping DNA fragments (contigs), were as much as 20% much greater than the size of the haploid genome.The ultimate diploid sequence was disperesed over 412 supercontigs, 146 homologous pairs, 119 phrap contigs, and one supercontig produced from two phrap contigs joined on the basis of GenBank sequence.The genome sequence shows many adaptations that are needed for environmental responding and sensing. Due to the fact that C. albicans is able to pass through the digestive tract, it requires it to be able to deal with extreme variations of pH. A number of genes associated with pH regulatory have been found in C. albicans.

Heterozygosity

The heterozygosity (the genetic variation in a population) of the Candida genome surpasses most microbes in other genomes and is commonly found in clinical isolates. The diploid assembly clearly shows the extent amount of heterozygosity in C. albicans. The entire population of C. albicans is said to have high polymorphisms. The average frequency of polymorphism is one in 237 bases. Many allelic differences have been found in C. albicans but their significance is not known. It is thought that these differences may increase genetic diversity and add to the development of drug resistance.

The polymorphisms found in C. albicans are distributed unevenly across its genome. Dissimilar single base polymorphisms yield two proteins that have differences in one or many amino acids that may give functional differences for each protein. This circumstance increases the amount of different types of proteins determined by the genome.

References

[1]↑Chibana, H., Magee, B. B., Grindle, S., Ran, Y., Scherer, S. & Magee, P. T. (1998) Genetics 149 , 1739-1752.

[2]↑Jones T, Federspiel NA, Chibana H, et al (May 2004). "The diploid genome sequence of Candida albicans". Proceedings of the National Academy of Sciences 101 (19): 7329–34.