Biotransformation of steroids by entomopathogenic strains of Isaria farinosa

Abstract

Background: Steroid compounds are very interesting substrates for biotransformation due to their high biological activity and a high number of inactivated carbons which make chemical modification difficult. Microbial transformation can involve reactions which are complicated and uneconomical in chemical synthesis, and searching for a new effective biocatalyst is necessary. The best known entomopathogenic species used in steroid modification is Beauveria bassiana. In this study we tested the ability of Isaria farinosa, another entomopathogenic species, to transform several steroids.

Results: Twelve strains of the entomopathogenic filamentous fungus Isaria farinosa, collected in abandoned mines located in the area of the Lower Silesian Voivodeship, Poland, from insects' bodies covered by fungus, were used as a biocatalyst. All the tested strains effectively transformed dehydroepiandrosterone (DHEA). We observed 7α- and 7β-hydroxy derivatives as well as changes in the percentage composition of the emerging products. Due to the similar metabolism of DHEA in all tested strains, one of them was selected for further investigation. In the culture of the selected strain, Isaria farinosa KCh KW1.1, transformations of androstenediol, androstenedione, adrenosterone, 17α-methyltestosterone, 17β-hydroxyandrost-1,4,6-triene-3-one and progesterone were performed. All the substrates were hydroxylated with high yield and stereoselectivity. We obtained 6β-hydroxyandrost-4-ene-3,11,17-trione, 15α,17β-dihydroxy-6β,7β-epoxyandrost-1,4-diene-3-one and 6β,11α-dihydroxyprogesterone. There is no evidence of either earlier microbial transformation of 17β-hydroxyandrost-1,4,6-triene-3-one or new epoxy derivatives.

Conclusions: Isaria farinosa has a broad spectrum of highly effective steroid hydroxylases. The obtained 7-hydroxydehydroepiandrosterone has proven high biological activity and can be used in Alzheimer's disease and as a key intermediate in the synthesis of aldosterone antagonists. Transformation of progesterone leads to high yield of 6β,11α-dihydroxyprogesterone and it is worth further study.

Keywords: Biotransformation; DHEA; Hydroxylation; Isaria farinosa; Progesterone.

Fig. 1

Structures of substates

Fig. 2

Isaria farinosa strains: a A moth cadaver found on a wall in an adit near Ciechanowice (Lower Silesian Voivodeship, Poland) overgrown by hyphae of Isaria farinosa © Jakub Grzeszczuk; b I. farinosa on PDA medium © Jakub Grzeszczuk; c Synnemata of I. farinosa grown on PDA medium © Jakub Grzeszczuk; d I. farinosa grown on cultivation medium © Tomasz Janeczko

Fig. 3

Transformation of DHEA in the culture of Isaria farinosa strains. Transformation conditions: 100 mL of cultivation medium (3% glucose, 1% bacteriological peptone) in 300 mL Erlenmeyer flasks, 24 °C, 150 r/min for 7 day

Fig. 4

Hydroxylation of adrenosterone by Isaria farinosa KCh J2 strain. Biotransformation conditions: 100 mL of cultivation medium (3% glucose, 1% bacteriological peptone) in 300 mL Erlenmeyer flasks, 24 °C, 150 r/min for 7 day

Fig. 5

Transformation of progesterone by Isaria farinosa KCh KW 1.1 strain. Biotransformation conditions: 100 mL of cultivation medium (3% glucose, 1% bacteriological peptone) in 300 mL Erlenmeyer flasks, 24 °C, 150 r/min for 7 day

Fig. 6

Biotransformation of 17β-hydroxy-androst-1,4,6-triene-3-one by Isaria farinosa KCh KW 1.1 strain. Biotransformation conditions: 100 mL of cultivation medium (3% glucose, 1% bacteriological peptone) in 300 mL Erlenmeyer flasks, 24 °C, 150 r/min for 7 day