Plant pathology. Reverend Berkeley's devil.
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DNA, Mitochondrial↗
Biomedical subjects
N P Money
Publications and source records attributed to N P Money.
Mechanics of solid tissue invasion by the mammalian pathogen Pythium insidiosum.
The relative significance of mechanical penetration versus the action of substrate-degrading enzymes during solid tissue invasion has not been established for any fungal disease. Pythium insidiosum is an oomycete fungus (or stramenopile) that causes a rare, but potentially lethal infection in humans and other mammalian hosts. Experiments with miniature strain gauges showed that single hyphal apices of this pathogen exert forces of up to 6.9 microN, corresponding to maximum pressures of 0.3 microN microm(-2) or MPa. Samples of cutaneous and subcutaneous tissue from fresh human cadavers displayed a mean strength (resistance to needle puncture) of 24 microN microm(-2), and a mean pressure of 30 microN microm(-2) was necessary to penetrate skin strips from slaughtered horses. These experiments demonstrate that P. insidiosum does not exert sufficient pressure to penetrate undamaged skin by mechanics alone, but must effect a decisive reduction in tissue strength by proteinase secretion.
Animals↗
Biophysics: fungus punches its way in.
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News↗
To perforate a leaf of grass.
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Colletotrichum↗
Invasive hyphal growth in Wangiella dermatitidis is induced by stab inoculation and shows dependence upon melanin biosynthesis.
Stab inoculation of agar medium with yeasts of the human pathogen Wangiella dermatitidis resulted in induction of invasive hyphae. Mechanical penetration of agar was indicated by the observation that an increase in medium gel strength slowed the rate of substrate invasion. A melanized wild-type strain (8656) exhibited much faster invasive growth through 2-8% agar than three melanin-deficient mutants. Inhibition of melanin synthesis in strain 8656 using tricyclazole resulted in a decrease in its rate of invasive growth, while scytalone restored melanin synthesis in the albino mel3 strain and boosted its rate of invasive growth. Earlier research established that cellular melanization is also associated with invasive hyphal growth in the mouse brain, and infections with strain 8656 are invariably lethal. Together, these in vitro and in vivo data indicate that biomechanical characteristics of fungi may be important determinants of virulence and disease progression in human and animal mycoses.
Antifungal Agents↗
Extension growth of the water mold Achlya: interplay of turgor and wall strength.
When hyphae of the water mold Achlya were subjected to osmotic stress, imposed with polyethylene glycol (PEG)-300 or sucrose, turgor pressure fell in proportion to the increase in external osmotic pressure. There was no evidence of turgor regulation, even over a period of days, yet the extension rate was unaffected until turgor was reduced to less than a third of the normal level of 0.6-0.8 MPa (6-8 bars). Measurements of the pressure at which the hyphae burst indicate that they respond to osmotic stress by softening their apical cell walls, sustaining extension growth despite reduced turgor pressure. The effect of osmolytes excluded by the wall was very different; superfusion of growing hyphae with PEG-6000 or dextran-6000 reduced turgor and stopped extension but did not induce wall softening. Furthermore, the hyphae did not resume growth during an hour or more of continuous exposure to these substances. Although the two classes of osmolytes have the same effect on turgor, they may induce different strains within the cell wall; this might then affect the capacity of the organism to detect the drop in turgor or to soften its cell wall. The interplay between turgor and wall strength supports the proposition that turgor supplies the driving force for extension and that production of the standard hyphal form requires a balance between hydrostatic pressure and a resistive cell wall.
Journal Article↗
Penetration of hard substrates by a fungus employing enormous turgor pressures.
Many fungal pathogens penetrate plant leaves from a specialized cell called an appressorium. The rice blast pathogen Magnaporthe grisea can also penetrate synthetic surfaces such as poly(vinyl chloride). Previous experiments have suggested that penetration requires an elevated appressorial turgor pressure. In the present report we have used nonbiodegradable Mylar membranes, exhibiting a range of surface hardness, to test the proposition that penetration is driven by turgor. Reducing appressorial turgor by osmotic stress inhibited penetration of these membranes. The size of the turgor deficit required to inhibit penetration was a function of the surface hardness. Penetration of the hardest membranes was inhibited by small decreases in appressorial turgor, while penetration of the softer membranes was sensitive only to large decreases in turgor. Similarly, penetration of the host surface was inhibited in a manner comparable to penetration of the hardest Mylar membranes. Indirect measurements of turgor, obtained through osmotically induced collapse of appressoria, indicated that the infection apparatus can generate turgor pressures in excess of 8.0 MPa (80 bars). We conclude that penetration of synthetic membranes, and host epidermal cells, is accomplished by application of the physical force derived from appressorial turgor.
Ascomycota↗
Responses of growth cones to changes in osmolality of the surrounding medium.
The possible involvement of osmotically generated hydrostatic pressure in driving actin-rich extensions of the cell surface was examined using cultures of chick neurons. Estimation of the excess internal osmotic pressure of chick neural tissue by vapor pressure deficit osmometry, and of the excess internal hydrostatic pressure in cultured chick neurons using a calibrated pressure pipette, gave upper limits of 10 mosM and 0.1 atmosphere (1 atmosphere = 101325 Pa), respectively. Increases in the osmolality of the medium surrounding cultured neurons by addition of sucrose, mannitol or polyethylene glycol by amounts that should eliminate any internal pressure not only failed to arrest the growth of filopodia but caused them to increase in length up to twofold in 3-5 min. Lamellipodia remained unchanged following hyperosmotic shifts of 20 mosM, but higher levels caused a small decrease in area. Reduction of osmolality by the addition of water to the culture fluid down to 50% of its normal value failed to show any detectable change in either filopodial length or lamellipodia area. These observations argue against an osmotic mechanism for growth cone extension and show that the growth of filopodia, in particular, is unlikely to be driven by osmotically generated hydrostatic pressure. In contrast to the short-term effects on growth cone morphology, the slower elongation of the neuritic cylinder showed a consistent osmotic response. Growth rates were reduced following addition of osmolytes and increased in rate (as much as sixfold) following addition of water to the culture medium.(ABSTRACT TRUNCATED AT 250 WORDS)
Actins↗
Osmotic Pressure of Aqueous Polyethylene Glycols : Relationship between Molecular Weight and Vapor Pressure Deficit.
Osmotic pressures (II) of aqueous solutions of polyethylene glycols (PEGs) of average relative molecular weight (M(r)) between 200 and 10,000 were measured using vapor pressure deficit osmometry. The relationships between molarity and II were described with high precision by second order polynomials for each of the PEGs studied. In contrast to previous reports, equivalent weights of different polymers in solution did not generate the same II; low M(r) PEGs generated a higher II than the higher M(r) PEGs. The effect of PEGs upon II represents an interaction between concentration and M(r).
Journal Article↗
Melanin synthesis is associated with changes in hyphopodial turgor, permeability, and wall rigidity in gaeumannomyces graminis var. graminis.
Mycelia of Gaeumannomyces graminis var. graminis form large cells called hyphopodia with deeply lobed, melanized walls. Like appressoria produced by other pathogens, hyphopodia develop on hydrophobic surfaces, but it is not clear that hyphopodia function as platforms for host penetration. In appressoria, melanin synthesis is linked to the generation of enormous turgor pressures that provide the necessary force for plant penetration. In the present study, hyphopodial turgor was measured in a wild-type strain of G. graminis var. graminis, a mutant exhibiting constitutive synthesis of melanin (referred to as the dark mutant), and a melanin-deficient strain (thr). These experiments demonstrate that hyphopodia of the wild-type strain generate higher pressures than the dark mutant and that nonmelanized thr hyphopodia generate minuscule internal pressures. Melanization of the wall is also associated with an increase in its rigidity. These data correlate with differences in wall permeability consistent with a recent model for turgor generation by appressoria.
Ascomycota↗