Z: The factor
2.3(RT/F)
Z-DNA
A left-handed helical form of dsDNA (cf. DNA) first observed in
oligomers of alternating deoxycytidine (dC) and deoxyguanosine (dG) in the
presence of high salt concentrations or ethanol. In these oligomers the strands
are connected by Watson–Crick base pairing, the sugar–phosphate backbones form
an irregular zig-zag (hence Z -DNA), there are ca. 12 bp/turn, and the
bases are relatively peripheral with the N7 and C8 positions of guanine
exposed; there is a single very deep helical groove corresponding to the minor
groove of B-DNA (see DNA). Stretches of alternating dC and dG in a plasmid can
undergo transition from right- to left-handed helical form
under physiological levels of ionic strength and super helical density;
the transition is driven by the torsional strain of negative super coiling and
is facilitated by C5 methylation of cytidine.Whether or not Z-DNA occurs in
vivo remains controversial.
Unlike B-DNA, Z-DNA is strongly immunogenic, and monoclonal antibodies
have been used for its detection in cells; however, the specificity of these
antibodies for Z-DNA is uncertain. The isolation of proteins which
preferentially bind Z-DNA rather
than B-DNA provides circumstantial evidence for the existence of Z-DNA
in vivo.
Z ring
see cell
cycle (b).
Z scheme
see
photosynthesis.
z value
The increase in temperature (°C) required for a 10-fold decrease in the
D Value.
Zadoks’ code
(Zadoks, Chang and Konzak decimal code) A code, designed primarily for computer
use, in which the various growth stages of cereals are represented by
numbers between 0 and 100: 0–9, germination; 10–19, seedling growth;
20–29, tillering; 30–39, stem elongation; 40–49, ‘booting’ (swelling of
the leaf sheath enclosing the
developing ear); 50–59, ear emergence; 60–69, flowering; 70–79, ‘milky’
stage of grain development; 80–89, ‘doughy’ stage of grain development; 90–99,
grain ripening.
Zalcitabine
see nucleoside reverse transcriptase inhibitors.
Zalerion
see
hyphomycetes; see also textile spoilage.
zanamivir
An
anti-influenza drug: a sialic acid analogue which can inhibit the viral
Neuraminidase
in influenza virus types A and B; the drug is inhaled
ZAP
Zoster-associated
pain: see herpes zoster.
zaragozic acids
Metabolites of certain fungi which are potent inhibitors of the enzyme
squalene synthase; they have potential uses as antifungal agents and/or as
therapeutic agents for lowering the levels of plasma cholesterol.
ZDV
Zidovudine
(see AZT).
a-zearalenol
see zearalenone.
zearalenone
(F-2 toxin) A mycotoxin produced by Gibberella zeae (Fusarium
graminearum) growing e.g. on damp cereal feedstuffs. It has
oestrogenic activity and can cause hyperoestrogenism (manifest by
vulvovaginitis and infertility) in sows;cattle and poultry can be affected,
though to a lesser extent.
Zearalenone can also act as a regulatory hormone in the sexual cycle of Gibberella.
Chemical reduction of zearalenone yields azearalenol,which is 4.8 times
more oestrogenic than zearalenone and has anabolic properties; it is used to
promote rapid weight gain in cattle and as an oestrogen substitute in
postmenopausal women.
zeatin
A naturally occurring Cytokinin:
6-(4-hydroxy-3-methylbut-2-enyl)-aminopurine. Its derivatives (e.g. zeatin
riboside) also function as cytokinins.
zeaxanthin
see
carotenoids.
zeaxanthin rhamnoside
see
xanthobacter.
ZEBRA
(Zta) Z EBV replication activator: the protein product of (immediate-early)
viral gene bzlf-1 which promotes replication of the EPSTEIN–BARR VIRUS in
latently infected B lymphocytes. ZEBRA can be induced by treating latently
infected B cells with e.g. anti-immunoglobulin, corticosteriods or ‘phorbol
ester’ (12-O-tetradecanoylphorbol-13-acetate, TPA).The lytic cycle in
latently infected B cells is also promoted by another transcription factor,
Rta, encoded by the immediateearly viral gene brlf-1 ; it has been
reported that the promoter of brlf-1 is activated by acetylation of
histones.
Zelleriella
See
opalinata.
Zenker’s fluid (modified)
A fixative:
mercuric chloride (5 g) and potassium dichromate (2.5 g) in distilled water
(100 ml) supplemented immediately before use with glacial acetic acid (5 ml).
Zephiran
see
quaternary ammonium compounds.
Zeta Plus filter
see filtration.
z-potential
(zeta potential;
electrokinetic potential)
Of e.g. a bacterial cell, or a charged colloid particle: the electrical
potential at the surface of shear – i.e., the surface of the cell or particle, including
adherent counterions and water molecules – which tends to move relative to
the surrounding medium when an external electrical field is applied; it is a
determinant of the electrophoretic migration rate of a cell etc. In media of
neutral or alkaline pH most bacteria carry a surface charge of negative
polarity – due to the ionization of surface groups. In many cases the
isoelectric point of a bacterium is ca. 3.0; at or near this pH such bacteria
tend toagglutinate spontaneously.
Zetapor membrane filter
see
filtration.
Zeugite
An early term for a cell or structure in which karyogamy ends
dikaryophase.
zicai
see laver.
zidovudine
Syn. AZT (q.v.).
Ziehl–Neelsen’s stain
An acid-fast stain. A heat-fixed smear is flooded with concentrated
carbolfuchsin, heated and kept steaming (not boiling) for 5 min, allowed to
cool, and rinsed in running water; the slide is then passed through several changes
of acid-alcohol (e.g. 3% v/v conc. HCl in 95% ethanol), washed in water, and
counterstained with e.g. 0.5% aqueous malachite green. After a final washing in
water the smear is dried and examined by microscopy. Acid-fast organisms stain
red, others green.
Ziemann’s dots
In erythrocytes infected with Plasmodium malariae: fine dots
sometimes observed on heavy staining with Romanowsky stains.
Zika virus
see flaviviridae.
zinc
(a) (microbial requirement) zinc is a heavy metal which is needed, in
trace amounts, for the activity of a number of microbial enzymes – e.g. Alcohol
dehydrogenase; de-acetylase (encoded by gene 1pxc in escherichia coli,
and involved in lipid A synthesis); some b-lactamases and superoxide
dismutases; the uvr a protein involved in dna repair; the zinc-endopeptidase tetanospasmin;
and carbonic anhydrase.
(b) (as an antimicrobial agent) In effective concentrations, zinc, and
certain of its compounds, are useful antimicrobial agents. For example, zinc
undecylenate and zinc oxide have been
used for treating certain superficial mycoses (e.g. athlete’s foot), and zinc
oxide is used as a mould inhibitor in paints. Zinc naphthenate can replace
copper naphthenate as a wood preservative but is apparently less effective.
Zinc dimethyldithiocarbamate has been used as a preservative in rubber (it also
serves as a vulcanization catalyst) and as an agricultural antifungal agent (ziram
– see also ZINEB). The precise mechanism of antimicrobial action may vary
with organism; thus, e.g. zinc appears initially to cause membrane damage in Saccharomyces
cerevisiae but may act by inhibiting intracytoplasmic proteins in another
yeast, Sporobolomycesroseus.
(c) (zinc chelation) The mammalian protein calprotectin is a
zinc-chelating agent whose bacteriostatic action presumably reflects its
ability to sequester zinc ions
zinc-endopeptidase
see tetanospasmin.
zinc sulphate flotation
see flotation.
zinc undecylenate
see undecylenic acid.
zinconazole
see azole antifungal agents.
zineb
(dithane z-78) zinc ethylenebisdithiocarbamate; this important agricultural
antifungal agent is used to control a wide range of plant pathogens, e.g. botrytis
spp, fulvia fulva (cladosporium fulvum), peronospora
spp, phytophthora infestans; it may be prepared as a wettable
powder – or may beprepared in the field by mixing nabam, zinc sulphate and
lime.
zipa protein
see cell cycle (b).
Zippering
see food poisoning (yersinia).
Ziram
See DMDC.
zoite
In coccidia: any of a range of stages in the life cycle –
e.g.cystozoite, endozoite, sporozoite etc.
zonal centrifugation
see centrifugation.
zonaria
see phaeophyta.
zone centrifugation
See centrifugation.
zone lines
In decaying wood: dark lines which are the edges of sheets of pigmented
fungal tissues in the wood.In wood rotted by e.g. Phellinus weirii the
coloration is due to a melanin-like pigment which apparently inhibits the
growth of microorganisms
antagonistic to P. Weirii
zoned reserve systems
Habitat areas that are protected from human alteration and surrounded by lands that are used and more extensively altered by human activity.
zoobiont
an animal symbiont. (cf. phycozoan.)
zoochlorellae
Green endosymbiotic algae present in various phycozoan associations. For
example, chlorella occurs e.g. In certain protozoa (e.g. Foraminifera, mayorella
viridis, paramecium bursaria, stentor polymorphus),
the freshwater sponge spongilla sp, the coelenterate hydra viridis,
the freshwater flatworm dalyellia viridis, and the freshwater clam anodonta.
The phycobiont generally supplies the zoobiont with products of photosynthesis
(e.g. Maltose in hydra and Paramecium, glucose in spongilla),
although the zoobiont may continue to feed. (see also elysia; cf.
Zooxanthellae.)
zooflagellates
Flagellates of the zoomastigophorea.
Zoogloea
(zooglea) A mass or film of cells embedded in a slimy matrix; zoogloeae
are formed e.g. by Zoogloea ramigera.
Zoogloea
A genus of gram-negative, aerobic, chemoorganotrophicbacteria (family
pseudomonadaceae) which occur e.g. In organically polluted freshwater habitats,
and in aerobically treated sewage .
Zooid
(microbiol.) (1) A motile spore. (2) Of a stalked ciliate(e.g. Vorticella):
the cell body, as opposed to the stalk.
zoology
[Gk. zoe, life + logos, a discourse]
The study of animals.
The study of animals.
zooplankton
[Gk. zoe, life + plankton, wanderer]
A collective term for the nonphotosynthetic organisms present in plankton.
A collective term for the nonphotosynthetic organisms present in plankton.
zoom microscope
A compound microscope in which magnification can be varied continuously
over a range of values.
Zoomastigophorea
A class of flagellate protozoa (subphylum mastigophora) which lack
chloroplasts and which are non-photosynthetic.
Zoonosis
Any infectious disease which can be contracted by man and in which the
pathogen is normally maintained in a reservoir consisting of animal (i.e. non-human)
population(s).
Zoonotic
pertaining to zoonosis.
Zoopagales
An order of fungi (class zygomycetes) which occur e.g. in soil and
water, and which are parasitic on e.g. certain amoebae, nematodes, and fungi;
the organisms form zygospores and give rise to asexual spores which are not
forcibly discharged. Genera: e.g. Bdellospora, Cochlonema, Piptocephalis,
Rhopalomyces, and Stylopage
Zoophagus
A genus of fungi of the peronosporales; Z. Insidians is an
aquatic species which captures and feeds on rotifers.
Zoophilic
Refers to a parasite or pathogen which preferentially infects animals.
Zoophthora
See entomophthorales.
Zooplankton
See plankton.
zoosporangium
a sporangium in which motile spores are formed.
Zoospore
a motile (flagellated) spore.
Zoothamnium
See Peritrichia.
Zooxanthella
See Zooxanthellae.
zooxanthellae
Endosymbiotic dinoflagellates found in various marine invertebrates,
including sea anemones (e.g. Anthopleura), giant clams (Tridacna),
jellyfish (Cassiopeia), reefforming tropical corals, and members of the
FORAMINIFERIDA and RADIOLARIA. (The loss of zooxanthellae from corals is a
useful indicator of stress due e.g. to pollution).All such endosymbiotic
dinoflagellates have been regarded as belonging to a single species, variously called
Symbiodinium microadriaticum, Gymnodinium microadriaticum, or Zooxanthella
microadriatica, but according to one report there are probably several distinct species. (See also phycozoan.)
[Evidence for heterotrophy by zooxanthellae in the sea anemone Aiptasia
pulchella, and its detrimental effects on the host under certain conditions].
zoster
syn. herpes zoster.
zoster-associated pain (ZAP)
see herpes zoster.
Zot toxin
(Vibrio cholerae) see bacteriophage CTX8.
Zovirax
syn. acyclovir.
Zschokkella
See myxosporea.
Zta
Syn. ZEBRA.
Zwischenferment
Glucose 6-phosphate dehydrogenase
(see Hexose Monophosphate Pathway).
zwoegerziekte virus
(zwogerziekte virus)
See Lentivirinae.
Zygnema
A genus of freshwater, unbranched filamentous green algae related to Spirogyra; each cell contains two
stellate chloroplasts. Akinetes may be formed.
Zygoascus
Agenus of filamentous, heterothallic fungi that include the teleomorphic
stages of Candida hellenica, C. inositophila and C.
steatolytica; type species: Z. hellenicus.
Zygoceros
See Diatoms.
Zygogonium
A genus of filamentous green algae related to Spirogyra. The filaments contain a purple pigment and grow e.g. on
damp peaty soils; some species are thermophilic, forming dense purple mats near
hot springs.
Zygomycetes
A class of fungi of the
zygomycotina; most zygomycetes are terrestrial saprotrophs, but some are
parasites or pathogens of animals (including insects), plants, and other fungi.
The typical thallus is a well developed, branched, coenocytic (aseptate) mycelium,
but some species form a septate mycelium, and some (see mucorales) are
dimorphic fungi; the cell wall contains chitin and/or chitosan. Characteristic
asexual reproductive structures include the sporangium and the
sporangiolum. Sexual reproduction typically involves zygospore formation
by the fusion of two morphologically similar gametangia; some species
exhibit homothallism, some heterothallism. Orders Dimargaritales (members form
merosporangia each containing two spores arranged End-to-end); Endogonales;
Entomophthorales; Kickxellales; Mucorales; Zoopagales.
zygomycosis
Any of a range of human
and animal diseases caused by fungi of the zygomycetes; the term currently
includes diseases formerly called phycomycosis (caused by ‘phycomycetes’),
mucormycosis (caused by fungi of the mucorales), and entomophthoromycosis
(caused by fungi of the entomophthorales). In all zygomycoses the invasive form
of the pathogen is an aseptate or sparsely septate, broad (e.g. 6–25 μm diam.),
hyaline mycelium; the hyphae may be branched and may assume bizarre forms.
Zygomycosis in man. Subcutaneous zygomycosis, in which
haptosporus (= B.
meristosporus). Nasofacial zygomycosis is
Zygomycosis in animals. Causal agents include some human
Zygomycotina
A subdivision of fungi (division eumycota) which form non-flagellate
asexually derived spores and which typically reproduce sexually by gametangial
copulation with the formation of zygospores (q.v.). Classes: trichomycetes and zygomycetes.
Zygophore
a short hyphal branch which develops into a progametangium.
Zygorhynchus
see mucorales.
Zygosaccharomyces
A genus of yeasts (family saccharomycetaceae) in which the cells are
globose, ellipsoidal or cylindrical; vegetative reproduction occurs by
multilateral budding. Pseudomycelium may be formed. The vegetative cells are
predominantly haploid (cf. SACCHAROMYCES). Ascus formation is preceded by
conjugation between individual cells (occasionally between a cell and its bud);
asci are persistent.
Ascospores: globose to ellipsoidal, 1–4 per ascus. Sugars are fermented
vigorously; NO−3 is not assimilated. Eight species are recognized: Z. bailii
(formerly e.g. Saccharomyces elegans), Z. bisporus, Z.
cidri, Z. fermentati, Z. florentinus, Z. microellipsoides,
Z. mrakii, and Z. rouxii (anamorph: Candida mogii ;
numerous synonyms, including e.g. Saccharomyces rouxii ).
Zygosporangium
see zygospore.
zygospore
A thick-walled, sexually-derived resting spore characteristic of fungi
of the zygomycotina. (zygospores are apparently not formed by e.g. Members of
the saksenaeaceae or of the amoebidiales.) The fusion of two gametangia (see
progametangium) gives rise to a prozygosporangium which develops into a zygosporangium
having a thick, multilayered, often highly ornamented wall; in at least
some zygomycetes the zygospore is known to develop as a separate structure within
the zygosporangium.the term ‘zygospore’ has been traditionally used to
refer to the zygosporangium together with its enclosed zygospore.
.
(zi-goat) [Gk. zygon,yolk, pair]
The diploid product of the union of haploid gametes in conception; a fertilized egg.
The diploid product of the union of haploid gametes in conception; a fertilized egg.
zygotene stage
see meiosis.
zygotic induction
The induction of a prophage when a chromosome containing that prophage
is transferred from a lysogenic conjugal donor (see lysogeny and bacterial
conjugation) to a recipient not lysogenized by the same (or a closely related)
bacteriophage; the induction occurs as a result of the absence of a phage
repressor protein in the recipient cell.
zygotic meiosis
Meiosis, in a zygote, preceding the formation of haploid vegetative
cells in a life cycle in which haplophase predominates. (cf. Gametic meiosis.)
zymase
Old term for the enzyme fraction isolated from disrupted yeast cells
which is capable of catalysing alcoholic fermentation.
Zymodeme
A subpopulation within a given taxon (e.g. genus) distinguished on the
basis of one or more isoenzymes.
Zymogen
(proenzyme) An inactive enzyme precursor that is usually converted to
the active form of the enzyme by proteolytic cleavage.
Zymogenous
Refers to those (predominantly transient or alien) microorganisms in a
given environment (e.g. soil) which exhibit an upsurge in growth (and hence in
numbers or biomass) on those occasions when the levels of nutrients increase,
or when a particular substrate becomes available; in the absence of suitable levels
of nutrients, relatively small numbers of such organisms may be capable of
existence, in that environment, in a dormant or starvation-resistant stage
zymogram
(1) A medium (e.g. a starch gel strip) which has been used for the
electrophoresis of a cell homogenate and which has been subsequently stained to
detect or quantify a given enzyme.
(2) A table showing the results
of tests which determine the ability of one or more organisms to ferment each
of a range
of carbohydrates.
Zymolyase
A commercial enzyme preparation obtained from culture filtrates of Arthrobacter
luteus. It contains endo-(1→3)- b-glucanase activity (‘Z-glucanase’) –
which is active against most (1→3)-b-glucans – and also some protease activity
(‘Zprotease’)
Zymolyase is used e.g.for investigating fungal (particularly yeast) cell
wall structure,for preparing yeast sphaeroplasts, etc.
Zymomonas
A genus (incertae sedis) of oxidase-negative, catalase-positive,
chemoorganotrophic, Gram-negative bacteria which occur e.g. as spoilage
organisms in alcoholic beverages (see e.g. CIDER spoilage) and which are used
in specific fermentations.
zymosan
An insoluble polysaccharide, found in the cell wall incertain yeasts,
which promotes complement fixation via the alternative pathway.
zymotype
A biotype characterized on the basis of a zymogram.
Zythia
A genus of fungi (order Sphaeropsidales) which include Gnomonia (Zythia)
fragariae, a pathogen of the strawberry plant. Elongated conidia are
formed in light-coloured pycnidia.