In Situ Probing of Endophyte Natural Products with DESI-Imaging Mass Spectrometry

Natural products are increasingly preferred for medicinal and therapeutic applications due to their safety and lesser toxicity over the synthetic compounds. Endophytes can be the economical source of natural bioactive metabolites. Endophyte-derived metabolites such as industrial and biomedical enzymes, alkaloids, steroids, flavonoids, and terpenoids have a wide range of biological activities. Endophytic microorganisms grow inside the living internal tissue of the plants. It is believed that exchange of genes between the endophyte and their host, probably occurred during the course of evolution, has enabled endophytes to mimic hosts’ chemistry. However, the process of harnessing natural products of endophyte is not only time-consuming but also tedious. The endophytic microorganisms are first isolated from the selected plant. Usually, a large number of isolates are obtained and tested by bioassay-based screening for desired activity. Moreover, the distribution of bioactive metabolites is varying in different plant tissues. The desired metabolites are isolated through a lengthy extraction and purification process. Desorption electrospray ionization mass spectrometry (DESI-MS) offers direct in situ imaging of metabolites of endophytic bacteria as well as fungi. Owing to its speed, accuracy and versatility, DESI-MS presents an opportunity for chemical profiling of endophytic microorganisms in an in situ culture, and it helps understand the temporal distribution patterns of secondary metabolites throughout the cell. This brief review highlights dynamics of endophytes and their natural products within the cell, imaging mass spectrometry (IMS) for in situ probing of metabolites of endophytic organisms, process workflow of DESI-MS, and reviews the identified secondary metabolites of endophytic microorganisms using DESI-MS platform in last 10 years.