Antibacterial activity and gas chromatography mass spectrometry (GC–MS)-based metabolite profiles of Celtis africana and its endophytic extracts

Abstract

Celtis africana Burm. f. is a medicinal plant native to Southern Africa and used for various ailments. Since crude extracts from mature leaves, stems, and fruits are the most common parts of this plant used for medicinal preparations, the same were selected for isolation of endophytes to assess the medicinal utility of their metabolite extracts as an extension to metabolite extracts from the different plant parts. Metabolites were extracted from the three plant parts using hexane, ethyl acetate, and dichloromethane (DCM) : methanol (MeOH) (1:1 v/v), while extracts from endophytes were extracted using hexane, ethyl acetate and DCM. Phytochemical and antimicrobial screening were performed using extracts from C. africana leaves, stems, and fruits. This was followed by identification of volatile compounds in plant and endophyte extracts using a two-dimensional gas chromatography coupled with time of flight mass spectrometry (GCxGC-TOF-MS). Four fungal endophytes from the Aspergillus genus and seven bacterial endophytes from the Kocuria, Bacillus, Arthrobacter, Staphylococcus, and Micrococcus genera were isolated from C. africana. Alkaloids, tannins, and reducing sugars tested positive in plant extracts while the presence of saponins and flavonoids was not observed. The hexane extract from the fruits was comparatively found to have the highest antibacterial activity with a minimum inhibitory concentration of 4 mg/mL on Staphylococcus aureus. Profiling of metabolites on GCxGC-TOF-MS showed the presence of several bioactive compounds in plant and endophytic extracts. Thirteen compounds found in plant extracts were also detected in the cultures of fungal and bacterial endophytes. It was concluded that C. africana fruit hexane extracts have antibacterial activity and that the plant’s endophytes can produce some of their host’s compounds. Furthermore, combining plant and endophytic crude extracts may extend the medicinal utility of C. africana.