Biological and morphological characteristics of Penicillium marneffei under oxidative stress

Abstract

Objective To observe the ultrastructure of dimorphic Penicillium marneffeiisolates from wild bamboo rats (Rhizomys pruinosus) in Guangxi region as well as from a patient with penieilliosis marneffei,and to compare their biological characteristics and anti-oxidative mechanisms.Methods Two Penicillium marneffei strains,including one isolated from wild bamboo rats (Rhizomys pruinosus) in Guangxi region and one from a patient with penicilliosis marneffei,were cultured with or without the presence of 2.0 mmol/L hydrogen peroxide in potato dextrose agar (PDA) at 25 ℃ and in brain-heart infusion (BHI) broth at 37℃ for seven days.The shape of colony and growth of both strains were observed.Light microscopy was carried out to study the morphology,and transmission electron microscopy to observe the ultrastructure,of both isolates.Results Ater incubation with hydrogen peroxide,there was a slowdown in the growth of both Penicillium marneffei isolates at both mycelial phase and yeast phase,with an increase in the production of pigment at mycelial phase at 25℃.No obvious changes were observed at 37 ℃ in the morphology of either the clinical isolate or the bamboo rat isolate when cultured with hydrogen peroxide compared with those cultured without hydrogen peroxide.Light microscopy showed attenuated spore formation by the clinical isolate when cultured at 25 ℃ with hydrogen peroxide,crenation of both isolates when cultured at 37 ℃ with hydrogen peroxide.Under a transmission electron microscope,the mycelial cells of both isolates exhibited smooth cell walls,intact cell membranes,with nuclei,mitochondria,endoplasmic reticulum,lipid body,vacuoles of various sizes in the cytoplasm at 25 ℃,and even microbodies at 37 ℃,when cultured without the presence of hydrogen peroxide.After incubation with hydrogen peroxide,the cell wall of both isolates became incomplete with defects in some areas and uneven thickness,the cell membrane discontinuous with shrinkages and projections,and the cytoplasm was inhomogeneous with obvious phagocytosis and numerous phagocytic vacuoles.Conclusions The clinical and bamboo rat isolates of Penicillium marneffei experience different biological and morphological changes under oxidative stress,hinting differences in antioxidative mechanism between them. Key words: Penicillium marneffei; Oxidative stress; Microscopy,electron,transmission; Guangxi