see amino acids.
Bases formed by the modification of guanine in tRNA; an example is wyosine, in which an additional ring is fused with the purine ring of guanine, the additional ring itself bearing a substituted hydrocarbon side-chain. Y bases occur e.g. in tRNA Phe in bacteria and yeasts.
Yaba monkey tumour poxvirus (Yaba virus)
A virus of the Poxviridae which can cause benign tumours in monkeys. Monkey handlers may become infected, infection typically resulting in the formation of a small nodular lesion which eventually regresses. Yaba virus replicates in the CAM and in certain types of cell culture.
See Food Poisoning (Yersinia).
A ‘health food’ marketed in Japan and in other countries; skim-milk containing glucose and an extract of Chlorella is inoculated with Lactobacillus casei and allowed to ferment at 37° C for several days. Sweeteners and flavourings may be added.
Yamaguichi-73 sarcoma virus
see avian sarcoma viruses.
see yield coefficient.
(framboesia; frambesia; pian)
A chronic infectious human disease caused by Treponema pallidum subsp pertenue; it occurs e.g. in tropical regions of America, Africa and the Far East, chiefly in areas where standards of hygiene are poor. Transmission occurs mainly by direct contact with infected persons or fomites; infection occurs via wounds and abrasions.
Syn. YGC AGAR.
A name often used specifically for Saccharomyces cerevisiae.A unicellular fungus that lives in liquid or moist habitats, primarily reproducing asexually by simple cell division or by budding of a parent cell.
Yeast extracts are water-soluble preparations (liquid, paste, powder or granules) obtained from e.g. brewers’ or Bakers’ Yeast (Saccharomyces cerevisiae), Kluyveromyces marxianus var. lactis, K. marxianus var. marxianus, or Candida utilis, Yeast extracts are rich in amino acids and peptides, B vitamins, trace elements, etc; they are used as condiments and food additives and as nutritional supplements in industrial fermentations, microbial growth media etc.
See dimorphic fungi.
A non-taxonomic category of fungi defined in terms of morphological and physiological criteria. The ‘typical’ yeast (e.g. Saccharomyces cerevisiae) is a unicellular saprotroph which can metabolize carbohydrates by fermentation and in which asexual reproduction occurs by budding.However, some yeasts (e.g. Schizosaccharomyces spp) divide by fission, and some can form a pseudomycelium and/or a true mycelium; some (e.g. Hansenula canadensis, Lipomyces spp, Sporobolomyces spp) are non-fermentative, and some (e.g. Candida albicans) can be pathogenic.
Yellow fever (yellow jack)
An acute infectious disease of man and other primates, endemic in parts of Africa and S. America; it is caused by a flavivirus
(1) Rice grains yellowed as a result of the growth and pigment formation of Penicillium islandicum. Consumption of such rice can lead to a mycotoxicosis (‘yellow rice disease’) due to the hepatotoxic, carcinogenic, anthraquinone pigment
luteoskyrin and other toxins (e.g. Chloropeptide).
(2) Rice yellowed by any of several pigment-forming Penicillium spp – e.g., P. islandicum, P. citreoviride (see CITREOVIRIDIN), P. citrinum (see citrinin).
Yellow rust (stripe rust)
A cereal disease caused by Puccinia striiformis. On wheat the disease is characterized by lines of lemon-yellow uredial pustules which occur between the veins on the upper (adaxial) surface of the leaf. On barley the symptoms are similar; in severe infections the pustules can also occur on the ears.
Any of a wide variety of plant diseases in which a major symptom is a uniform or non-uniform (e.g. striped or mottled) yellowing of leaves and/or other plant components.(cf. chlorosis.) yellows may be caused by fungi (e.g. one form of celery yellows), viruses (diseases in many plants – see e.g. sugar beet yellows virus), bacteria (e.g. coconut lethal yellowing), or protozoa (e.g. hartrot, phloem necrosis).
A genus of Gram-negative bacteria of the family Enterobacteriaceae (q.v.). Yersinia spp are parasites and pathogens in man.
Any disease of man or animals caused by a species of Yersinia.
See Avian Sarcoma Viruses and Oncogene.
YGC agar (YDC agar)
An agar medium containing yeast extract, D-glucose, and precipitated chalk; it is used e.g. as a generalpurpose medium for plant-pathogenic bacteria (e.g. Erwinia spp).
Yeast extract–malt extract broth, a medium for the culture of yeasts; it contains yeast extract, malt extract, peptone and glucose. YM agar is YM broth solidified with 2% agar.
Yeast extract–mannitol agar, used e.g. for the culture of Rhizobium spp.
yoghurt (yogurt, yaourt)
A food made by fermenting milk with a mixed culture of Lactobacillus bulgaricus and Streptococcus thermophilus; the bacteria produce lactic acid and other flavour components (traces of acetaldehyde, diacetyl and acetic acid.
The stored food in egg cells that nourishes the embryo.
One of four extra embryonic membranes that supports embryonic development; the first site of blood cells and circulatory system function
See food poisoning (Yersinia).
See mating type.