Light influence on melaninogenesis of Cladosporium cladosporioides (Fresen) de Vries

Abstract

Biocontrol agents (BCAs) for the control of fungal diseases and pests has been the focus in the development of, thus, the agrochemical industry has refocused priorities on integrated control to include the use of BCAs in research and programmes for disease and pest control. The mechanism of action has often included direct antagonism between the BCA and fungal pathogen, competitive exclusion of the pathogen by niche occupation, production of secondary metabolites, hyperparasitism, and the production of volatile organic compounds (VOCs). It is considered as a characteristic of antagonist, to present more than one mechanism, because in this way, their chances of success are increased. The present study, objectived to evaluate, in vitro, competition between the fungus considered a bioprotective agent of the coffee quality Cladosporiumcladosporioides (Fresen) de Vries and the potentially toxigenic fungus Aspergillus ochraceus G. Wilh. Competition between isolates of C. cladosporioides and A. ochraceus was evaluated in vitro conditions by adding conidia aliquotas in Petri dishes containing PDA (potato, dextrose, ágar) culture medium.The antagonist relationship between isolates was observed in Olympus SZX7TR-ILA trinocular stereoscopic microscope coupled to a camera and in scanning electron microscopy ZEISS ®. The fungus C. cladosporioides (Fresen) de Vries, showed its antagonism on potencialmycotoxigenic fungus A. ochraceus by of antibiosis and hyperparasitism mechanisms.

Microbial Interaction with Clay Minerals and Its Environmental and Biotechnological Implications

“…We found that the presence of 0.5% (w/v) montmorillonite in the medium changed some key growth parameters of C. cladosporioides 396 grown on the glucose-containing liquid medium [206]. Traditionally used in the studies of microbial growth kinetics in an aqueous environment, the empirical Monod model relates the growth rate to the concentration of a single growth-controlling (or limiting) substrate via two main parameters, the maximum specific growth rate (µ max ) which is a rate at which the substrate concentration is not limiting, and the substrate affinity constant (K s ) or half-saturation constant, equal to the growth limiting substrate concentration when the growth rate is half of µ max [207][208][209].…”

“…The biological effects of clay minerals on the melanin-producing microscopic fungi are of particular interest because this group of dark pigmented microorganisms is well adapted to mineral substrata and harsh environments, commonly occurring in soils and on the rock surfaces, and might play a significant role in pedogenesis because the melanin pigment, in terms of its chemical nature, is one of the most important precursors of the humic substances in soil [65,85,105,111,175,[196][197][198]. It is well known that fungal melanins and other phenolic polymers possess many potential metal-binding sites with oxygen-containing groups including carboxyl, phenolic and alcoholic hydroxyl, carbonyl and methoxyl groups [129,156].…”

“…Cladosporium spp. are thought to be able to withstand various physical and chemical stresses thanks to the melanin in the cell wall comprising about 20-30% of biomass [196]. Because of their ability for melanin synthesis this group of fungi has attracted attention of the researchers, and the strain Cladosporium cladosporioides 396 has been studied as a potential producer of melanin preparation with radioprotective, antioxidant and detoxifying properties for medical use and also as a biosorbent of toxic metals and radionuclides [157,[203][204][205].…”

“…Regarding the microbial interactions with clay minerals, there are a few experimental studies on the biological effects of clay minerals on the growth of melanin-producing microfungi, including Cladosporium cladosporioides 396, carried out using a submerged culture technique [157,175,185,205,206].…”

“…In the series of our experimental studies on the clay mineral effects on melanin-producing fungi, we focused mainly on the biotechnologically relevant strain C. cladosporioides 396, investigating the impact of montmorillonite on the physiological parameters of fungal growth in submerged culture, the morphological changes of fungal growth, the melaninogenesis and also the metal sorption properties of the fungal-clay composites [157,175,205,206].…”