Biotransformation of betulin to betulinic acid by Fusarium lacertarum BRF59, an endophytic fungus isolated from the genus Betula

Betulinic acid (BA), a betulin derivative, is an important plant-based natural product. BA has many biological activities and attracts attention especially as a promising antitumour drug. Extraction from plants or semi-synthesis from betulin are the common methods to obtain BA, but these methods have some drawbacks. In recent years, microbial biotransformation of betulin to BA has been anticipated as an alternative method. Betulin is abundant in the outer bark of birch (Betula spp.) and obtained from these plants, however endophytes of Betula spp. have not been investigated for biotransformation of betulin to BA before. Therefore, this study aimed to investigate the culturable endophytes of Betula pubescens var. litwinowii (Doluch.) Ashburner & McAll and to determine their biotransformation capacity of betulin to BA. To this end, bacterial and fungal endophytes were isolated from the surface-sterilized root, stem, and branch samples. A total of 37 endophytes (11 bacteria and 26 fungi) were identified by polyphasic approach. All endophytes were screened for the biotransformation of betulin to BA. Betulin and BA content of the extracts were determined by RP-HPLC analysis. Two different bacterial and fungal biotransformation processes were designed. It was found that the fungus BRF59 produced BA via betulin biotransformation under the Fungal Biotransformation Process-2 when the fungus was acclimatized to betulin before biotransformation, and glycerol was used as a carbon source, instead of glucose, during bioprocess. The highest BA yield and BA concentration was obtained as 12.22±0.94 % and 80.85±2.64 µg/ml, respectively, under non-optimized conditions. The fungal isolate BRF59, belonging to the genus Fusarium according to ITS analysis, was further identified based on RPB2 sequence analysis and found that Fusarium lacertarum. In conclusion, this study demonstrated that betulin was biotransformed to BA by an endophytic fungus isolated from the genus Betula for the first time. F. lacertarum BRF59 might be a good candidate for production of BA through betulin biotransformation and, using glycerol as a carbon source during biotransformation might enable this by-product to convert value-added chemical. [Display omitted] •Culturable endophytes of Betula pubescens var. litwinowii (Doluch) was investigated.•Biotransformation of betulin to betulinic acid by endophytes was investigated.•Fusarium lacertarum BRF59 produced betulinic acid via betulin biotransformation.•Th