ABSTRACT The fungal pathogen Candida albicans produces dark-pigmented melanin after 3 to 4 days of incubation in medium containing l -3,4-dihydroxyphenylalanine ( l -DOPA) as a substrate. Expression profiling of C. albicans revealed very few genes significantly up- or downregulated by growth in l -DOPA. We were unable to determine a possible role for melanin in the virulence of C. albicans . However, we showed that melanin was externalized from the fungal cells in the form of electron-dense melanosomes that were free or often loosely bound to the cell wall exterior. Melanin production was boosted by the addition of N -acetylglucosamine to the medium, indicating a possible association between melanin production and chitin synthesis. Melanin externalization was blocked in a mutant specifically disrupted in the chitin synthase-encoding gene CHS2 . Melanosomes remained within the outermost cell wall layers in chs3 Δ and chs2 Δ chs3 Δ mutants but were fully externalized in chs8 Δ and chs2 Δ chs8 Δ mutants. All the CHS mutants synthesized dark pigment at equivalent rates from mixed membrane fractions in vitro , suggesting it was the form of chitin structure produced by the enzymes, not the enzymes themselves, that was involved in the melanin externalization process. Mutants with single and double disruptions of the chitinase genes CHT2 and CHT3 and the chitin pathway regulator ECM33 also showed impaired melanin externalization. We hypothesize that the chitin product of Chs3 forms a scaffold essential for normal externalization of melanosomes, while the Chs8 chitin product, probably produced in cell walls in greater quantity in the absence of CHS2 , impedes externalization.

Melanosome

10.1128/ec.00051-10

Cite

Citations (101)

Parasites of the black scabbard fish, Aphanopus carbo Lowe, 1839 from Madeira

Bulletin of the European Association of Fish Pathologists (1996)

Graça Costa J. C. Eiras James C. Chubb K. MacKenzie B. Berland

Source

Cite

Citations (14)

Selective pressures and parasite strategies.

C. Combes Kirill V. Galaktionov О. Н. Пугачев K. MacKenzie Karl Skírnisson

Source

Cite

Citations (0)

Hyphal Orientation of Candida albicans Is Regulated by a Calcium-Dependent Mechanism

Current Biology (2007)

Alexandra Brand Scott Shanks Vanessa M.S. Duncan Meng Yang K. MacKenzie

Eukaryotic cells from fungal hyphae to neurites that grow by polarized extension must coordinate cell growth and cell orientation to enable them to exhibit growth tropisms and to respond to relevant environmental cues. Such cells generally maintain a tip-high Ca(2+) cytoplasmic gradient, which is correlated with their ability to exhibit polarized tip growth and to respond to growth-directing extracellular signals. In yeast and other fungi, the polarisome, exocyst, Arp2/3, and Spitzenkörper protein complexes collectively orchestrate tip growth and cell polarity, but it is not clear whether these molecular complexes also regulate cell orientation or whether they are influenced by cytoplasmic Ca(2+) gradients. Hyphae of the human pathogenic fungus Candida albicans reorient their growth axis in response to underlying surface topography (thigmotropism) and imposed electric fields (galvanotropism). The establishment and maintenance of directional growth in relation to these environmental cues was Ca(2+) dependent. Tropisms were attenuated in media containing low Ca(2+), or calcium-channel blockers, and in mutants where calcium channels or elements of the calcium signaling pathway were deleted. Therefore galvanotropism and thigmotropism may both be mediated by localized Ca(2+) influx at sites of polarized growth via Ca(2+) channels that are activated by appropriate environmental signals.

Tip growth

Exocyst

Cell polarity

Organelle

10.1016/j.cub.2006.12.043

Cite

Citations (145)

Application of a low oil pre-harvest diet to manipulate the composition and quality of Atlantic salmon, Salmo salar L.

Aquaculture (2004)

P.C. Morris C. Beattie B. Elder John Finlay P. H. Gallimore

Commercial fish feed

10.1016/j.aquaculture.2004.11.011

Cite

Citations (15)