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Fungal Lipids
Published in Rajendra Prasad, Mahmoud A. Ghannoum, Lipids of Pathogenic Fungi, 2017
Changes in amounts of free and esterified sterols have been correlated with conservation of sterols during alternating phases of the growth cycle. Parks et al.,143 after observing increased esterification of sterols upon entry into stationary phase and rapid hydrolysis to free ergosterol when transferred to fresh medium, suggested that there was a critical and transient requirement for ergosterol in the actively growing fungal cells and that esterification conserves sterols for availability in active growth phases. Studies on mutants defective in sterol synthesis often show “an accommodating physiological or genetic adjustment” of phospholipid content, allowing growth without sterol.143 The strict requirement of sterols by some members of the Pythiaceae, for example, has been thrown in doubt by the apparent induction of oospores on defined media supplemented with phospholipids. Detailed examination by Kerwin and Duddles suggested that only traces of sterols were necessary for sparking and critical domain roles, acting synergistically with phospholipids containing unsaturated fatty acid moieties to induce oospore formation.146 In Pythium ultimum, enrichment of the phospholipid fraction of cell lipid with unsaturated fatty acids, taken up from exogenous lipid, had promoted oospore induction while enhanced levels of unsaturated fatty acids in the neutral lipids had increased oospore viability.
Pythium insidiosum keratitis: Review of literature of 5 years’ clinical experience at a tertiary eye care center
Published in Seminars in Ophthalmology, 2023
Pratima Vishwakarma, Bhupesh Bagga
There are two phases (asexual and sexual) in the life cycle of a typical Pythium sp., which are excited by different environmental circumstances.8 The asexual cycle is characterized by the generation of sporangia which may either propagate directly to form a germ tube (direct germination) or by cytoplasmic cleavage it may get differentiated into uninucleate, biflagellate zoospores (indirect germination).7 Upon interaction with a mammalian host, their flagella are lost, they encyst followed by secretion of an adhesive-like material that helps to keep them attached to the host. These encysted zoospores can develop a germ tube that points toward the wound and penetrates the host tissues, leading to pythiosis.9 The sexual cycle generates thick-walled oospores that can survive under harsh environmental conditions. These are produced by a process called oosporogenesis in which a female oogonium and a male antheridium are produced that later fuses leading to fertilization and thereby to the development of an oospore. These resting spores can germinate under suitable conditions to produce single or multiple germ tubes which can then form sporangia thereby recapitulating the asexual cycle of the pathogen.8(Figure 1)