Synchronous initiation and maturation of Aspergillus niger conidiophores in culture

Abstract

Synchronous development of Aspergillus niger conidiophores was obtained by using a system in which complete development was divided into four distinct morphogenetic stages, (i) Conidiophore initiation occurred in a low nitrogen (LN) medium, but not in a medium in which both glucose and nitrogen were exhausted simultaneously and not in LN medium under oxygen-limited conditions, (ii) Conidiophore growth occurred without exogenous nitrogen although exogenous glucose was essential. In addition, development was enhanced by a colonial growth form indicating that translocation from mycelium to the conidiophore was an important feature of this stage. During stages (i) and (ii) there was the abundant production of a carotenoid pigment, (iii) Vesicle and phialide formation did not occur on conidiophores formed in LN medium. Transfer of aborted conidiophores to a medium containing a nitrogen source and a tricarboxylic acid cycle intermediate as a carbon source stimulated vesicle and phialide formation. There was a concurrent stimulation of respiration and an increase in RQ, value. Conidiospore formation was inhibited and this resulted in vesicle and phialide proliferations, (iv) Heavy conidiospore production occurred on a further transfer of conidiophores with vesicles and phialides to a glucose nitrate medium. Conidiophore initiation, vesicle and phialide formation and carotene production were inhibited by reduction of the oxygen supply rate although vegetative growth could continue.