Microbiology (1 996), 142, 51 7-523 Printed in Great Britain Polyamines as modulators of microcycle conidiation in Aspergillus flavus N. Khurana,’ R. K. Saxena,’ Rani Gupta’ and M. V. Rajam’ Author for correspondence: M. V. Rajam. Tel: +91 11 606392. Fax: +91 11 688 6427/688 5270. e-mail : bicdusc@dbt.ernet.in Departments of Microbiology’, and Genetics*, University of Delhi, South Campus, Benito Juarez Road, New Delhi 110021, India Since polyamines (PAS) play a potential role in the regulation of growth and developmental processes in a wide variety of organisms, we have examined the influence of the PAS putrescine (Put) and spermidine (Spd) and the PA biosynthetic inhibitors a-difluoromethylornithine (DFMO), a- dif luoromethylarginine (DFMA), methylglyoxal bis-(guanylhydrazone) (MGBG) and cyclohexylamine(CHA), singly and in combinations on microcycle conidiation (MC) in Aspergillus flaws. The exogenous application of the diamine Put (concentrations ranging from 01 to 5 mM) caused a sharp decline of MC in a dose-dependentfashion, but induced vegetative growth. However, the triamine Spd (01-5 mM) had a minimal effect on MC and induced a shift from MC to normal conidiation. PA inhibitors, especially DFMO, MGBG and CHA, produced greater inhibition of MC and complete inhibition of MC was observed at 5 mM of these inhibitors. DFMA even at 5 mM had only a weak inhibitory effect on MC. DFMO also inhibited conidial germination and germ tube growth. MGBG and CHA, while having an inhibitory effect on MC, induced vegetative growth. The inhibitory effect of PA inhibitors was partially reversed by exogenous Put or Spd, with Spd being more effective than Put. The analysis of free PA levels during various phases of MC revealed that undifferentiated spores contained a high Put/Spd ratio and there was a dramatic decrease in Put/Spd ratio before and during microcycle conidiophore maturity. The change in spermine titres could not be detected. These observations imply that Put is essential for vegetative growth, while Spd is involved in MC, and that a low Put/Spd ratio seems to be important for spore differentiation to MC. Keywords : AspergdhssfEavus, development, microcycle conidiation, polyamines, polyamine biosynthesis inhibitors INTRODUCTION Microcycle conidiation (MC) (a condensed developmental process of conidiation without any intervening vegetative mycelium) has been reported in Aspergillus niger using temperature manipulation by Anderson & Smith (1971a, b). Since then attempts have been made to induce this phenomenon in other Aspergillm spp. and fungi by manipulating culture conditions and/or nutrient factors (Maheshwari, 1991). Earlier, we reported MC on a novel medium, D-glucose soluble starch (D-GSS) in Aspergillus spp. (Saxena et a!., 1992) and under light-independent Abbreviations: CHA, cyclohexylamine; DFMA, a-difluoromethylarginine; DFMO, a-difluoromethylornithine; D-GSS, D-glucose soluble starch; MC, microcycle conidiation; MGBG, methylglyoxal bis-(guanylhydrazone); PA(& polyamine(s); Put, putrescine; Spd, spermidine; Spm, spermine. conditions in Tricboderma spp. (Khurana et al., 1993). Although some work has been done on the induction and on the ultrastructure, the internal events regulating microcycle differentiation are still not fully understood (Maheshwari, 1991). However, our work on MC in D- GSS medium implied that the osmolarity of medium can regulate MC, at the transcriptional level (Khurana et al., 1992). Polyamines (PAS), spermidine (Spd) and spermine (Spm) and their precursor the diamine putrescine (Put) are involved in a variety of growth and developmental events in a wide range of organisms, including fungi (Rajam & Galston, 1985; Rajam et al., 1985, 1986, 1989; Tabor & Tabor, 1985; Walters, 1987; Singhania, 1991 ; Rajam, 1993). No attempts so far have been made to demonstrate the possible role of PAS in MC. Thus, we have examined the influence of exogenous PAS Put and Spd, and specific 0002-0087 Q 1996 SGM 517