Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: May 8, 1997
Publication Date: N/A
Technical Abstract: Details of the pentaketide melanin pathway have been elucidated in several brown to black human and plant pathogenic fungi, but little is known about pigmentation in green colored fungi. In the present study, we used three pigment-deficient mutants grown on asparagine-sucrose-agar medium to study the biosynthesis of the bluish-green pigment in A. fumigatus. The three mutants, B-5233/RGD4-2, B-5233/RGD3-1, and B5233/RGD10-1 were reddish brown in color when grown at 25 C for 7 days on the alkaline medium. B-5233/RGD4-2, a putative scytalone dehydratase deficient mutant, accumulated flaviolin and scytalone in the medium. This confirmed that the mutant was unable to enzymically dehydrate scytalone to 1,3,8-trihydroxynaphthalene, the next intermediate in the pentaketide pathway. When B-5233/RGD4-2 and the parent strain B-5233 were grown on medium, containing 30 ug/ml tricyclazole (a known inhibitor of pentaketide melanin synthesis), flaviolin but not scytalone accumulated in the medium. This showed that tricyclazole prevented the reduction of 1,3,6,8-tetrahydroxynaphthalene (1,3,6,8-THN) to scytalone, and as 1,3,6,8-THN accumulated, it was oxidized to flaviolin. The putative reductase mutants (B-5233/RGD3-1 and B-5233/RGD10-1) also accumulated flaviolin but not scytalone. This confirmed that they were unable to reduce 1,3,6,8-THN to scytalone. The results of this study show that certain enzymic steps in the synthesis of the green pigments are identical to those previously elucidated in the synthesis of various brown to black pigments of fungi.