Pichia kudriavzevii

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Classification

Domain: Eukaryota

Phylum: Ascomycota

Class: Saccharomycetes

Order: Saccharomycetales

Family: Pichiaceae

Genus: Pichia

[Others may be used. Use NCBI link to find]

Species

NCBI: Taxonomy

Pichia kudriavzevii

Image of Pichia kudriavzevii (6)

Description and Significance

Pichia kudriavzevii is the teleomorph of the Candida krusei. A teleomorph is the sexual reproduction stage of an organisms, meaning Pichia kudriavzevii reproduces sexually through the fusion of haploid cells (15). The asexual state of a fungi is called an "anamorph" (1). The yeast was first named Issatchenkia orientalis by V.I. Kudryavtsev in 1960 and was changed to Pichia kudriavzevii in 1965 (2).

The shape of cells can be oval or ellipsoidal to elongate. (3) It is very abundant in the environment and commonly found in soil, on the skins of fruits and even in fermented beverages. Pichia kudriavzeii can remain metabolically active at temperatures as high as 45°C and in pHs as low as 2 (3 and 4). It produces ethanol at a high yield, which is very useful for the biofuel industry (3). Like most yeast, Pichia kudriavzeii is involved in the fermentation of wine and beer; however, it is also very valuable in cocoa bean heap fermentation, creating a greater flavor and aroma for cocoa beans. It can be a pathogen under some circumstances and yet there are only a few pathogenic cases documented because Pichia kudriazveii is only documented to infect those with an immunodeficiency (5).

Genome Structure

P. kudriavzevii has average eukaryotic chromosome structure and DNA. As the organism undergoes meiosis, two pairs of chromosomes recombine and separate. The chromosome is found to be 3 to 8 bands in length (7). The linear DNA is found in the nucleus, with a standard code. In other words, AUG is used as the start codon and UAA/UGA/UAG are used as the stop codons. On average, the nuclear DNA contains approximately 10 million base pairs, with around 5 thousand being protein-coding genes. The GC content is around 38% with 3 of the genes coding for phytase, an enzyme that catalyzes the hydrolysis of phytic acid and is involved in the syntrophic relationship between P. kudriavzevii and plants that utilize phosphorus. (7). The mitochondria DNA is circular with approximately 51 thousand base pairs (8).

Fermentation of Xylose: Xylose is inputted into the pentose phosphate pathway and converted into fructose (this is unique to Pichia kudriavzeii). Fructose is passed through the glycolysis pathway, resulting in the release of energy and pyruvic acid. Under the right conditions, pyruvic acid can be converted into ethanol (2).

Cell Structure, Metabolism and Life Cycle

Like many other yeast cells, the Pichia kudriavzevii cell is constructed with a cytoplasm, nucleus, cell membrane, cell wall, mitochondria and vacuole (9). It can use glucose, sucrose, galactose, fructose, and mannose as food resources, although glucose is the most documented resource. Something unique to P. kudriavzeii is its ability to hydrolyze phytic acid from phytase. Phytic acid cannot be digested by most mammals so this feature is particularly helpful in human food (3).

Although many species of yeast have the ability to produce ethanol, not many can produce it from xylose. Xylose is a sugar found in wood, meaning this can used as an alternative for ethanol production, which is particularly useful in the biofuel industry. Xylose is converted to fructose and the fructose enters the glycolysis pathway. Pyruvic acid and energy are the products of glycolysis and, under the right conditions, pyruvic acid will be converted to ethanol (2).

Yeast cells exist in two forms when they go through the sexual reproduction. They are Haploid dwarf cell and Diploid large cell. There are two mating types of haploid cell which are called “a” and “α”. If two mating types contact each other, they will form gametangia and start sexual reproduction. (14)

Ecology and Pathogenesis

P. kudriavzevii can be found in soil and on the outside of fruits and vegetables, often in the presence of other Pichia species. Although it is found on the outside of produce, it is not considered a species that is responsible for food spoilage (10). Instead, P. kudriavzevii can be helpful when developing an environmentally-friendly, bio-based candidate for food preservative and bio-control. It produces P. kudriavzevii RY55 toxin, which can kill several human health pathogens and contribute to food preservation (11). It can also be isolated from many different fermentations ranging from fruit juice to cocoa bean heap and it is particularly useful in amplifying the aroma of chocolate (3).

Since this organism contains 3 genes that code for phytases, there is a syntrophic relationship between P. kudriavzevii and plants. For instance, the phytases present in the yeast degrade phytate present in soil, improving the amount of phosphate intake from the plants. As a result, there is a reduction in the amount of phosphorus fertilizer needed (7).

P. kudriazvevii can be present without causing harm, however, in some cases it is pathogenic. Some would consider P. kudriavzevii to be a "opportunistic pathogen." Specifically, P. kudriavzevii infects those that are immunodeficient. A pathogenic P. kudriavzevii can lead to mastitis (infection of the breast tissue) in mammals, but this type of disease is most commonly found in dogs and cattle (5). There are few cases of humans being severely impacted by the presence of P. kudriazvevii; however, there was an outbreak of sepsis due to P. kudriazvevii in a neonatal intensive care unit in 2017. This was the first documented case of neonatal sepsis due to P. kudrizvevii. On the other hand, the anamorph of P. kudrizvevii (Candida species) is one of the most common causes of late on-set fungal sepsis, so it can be inferred that more cases of P. kudrivzevii-induced sepsis will start to appear (12). Some general symptoms of sepsis include fever, hypothermia, fast heart rate, swelling, and high blood glucose levels. Some symptoms specific to sepsis are (but are not limited to) a high white blood cell count, low oxygen level, low urine output, high lactate in blood, and a decrease in capillary filling (13)

References

1. Guarro, J., Gené, J., and Stchigel, A. 1999. Developments in Fungal Taxonomy. Clinical Microbiology Review 12(3):454-500.
2. Hello, My Name is Pichia kudriavzevii. 2014. Eureka Brewing; [2014; February 16, 2014]. https://eurekabrewing.wordpress.com/2014/02/16/hello-my-name-is-pichia-kudriavzevii/
3. Oberoi, H., Babbar, N., Sandhu, S., Dhaliwal, S., Kaur, U., Chadha, B., and Bhargav, V. 2012. Ethanol production from alkali-treated rice straw via simultaneous saccharification and fermentation using newly isolated thermotolerant Pichia kudriavzevii HOP-1. Journal of Industrial Microbiology & Biotechnology 39(4):557-556.
4. Greppi, A., Saubade, F., Botta, C., Humblot, C., Guyot, P., and Cocolin, L. 2017. Potential probiotic Pichia kudriavzevii strains and their ability to enhance folate content of traditional cereal-based African fermented food. Food Microbiology 62:169-177.
5. Hurst, C. 2016 The Rasputin Effect: When Commensals and Symbionts Become Parasitic. pp:292
6. Candida Krusei. 2014. UC Davis: Viticulture and Enology; [2016; November 29, 2016]. http://wineserver.ucdavis.edu/industry/enology/winemicro/wineyeast/candida_krusei.html
7. Chan, G., Gan, H., Ling, H., and Rashid, N. 2012. Genome sequence of Pichia kudriavzevii M12, a potential producer of bioethanol and phytase. Eukaryot Cell 11(10).
8. Bae, J.; Han, J.; Jeong, H.; Ko, H.; Ko, H.; Park, H.; Sohn, J.; Sung, B. 2018. Draft Genome Sequence of a Multistress-Tolerant Yeast, Pichia kudriavzevii NG7 Genome Announc 6:e01515-17.
9. Cell Structure of Yeast (With Diagram) | Fungi. Biologydiscussion.com; http://www.biologydiscussion.com/yeasts/cell-structure-of-yeast-with-diagram-fungi/58253
10. Fleet, G. 2011. The Yeasts. Elsevier. IBSN: 978-0-444-52149-1.
11. Bajaj, B.; Raina, S.; Signh, S. 2013. Killer Toxin From a Novel Killer Yeast Pichia kudriavzevii RY55 with Idiosyncratic Antibacterial Activity. Journal of Basic Microbiology. 53: 645-656.
12. Nagarathnamma, J. et al. 2017. Outbreak of Pichia kudriavzevii fungaemia in a Neonatal Intensive Care Unit. Journal of Medical Microbiology. 66: 1759-1764.
13. Symptoms. Sepsis.org; https://www.sepsis.org/sepsis/symptoms/.
14. Karki, G. 2017. Yeast: Morphology and Life Cycle; [2017; November 18, 2017] http://www.onlinebiologynotes.com/yeast-morphology-life-cycle/.

Edited by Kelsey McKenzie and Hongxi Lyu students of Jay Lennon for BIO L472 Microbial Ecology, 2018, Indiana University Bloomington.