Studies on Endophytic Microorganisms: Their Phylogenetic Analysis, Biomedical and Agricultural Applications

Endophytes are fungal and bacterial microorganisms that colonize the internal tissues of plants without damaging the host plants. They are ubiquitous and diverse in plant species, but remain under-explored. A number of studies have shown that endophytes constitute a robust source of novel secondary metabolites for a wide range of biological applications, both medical and agricultural. Plants with rich ethnobotanical history are considered resourceful candidates for the investigation of endophytic microorganisms as a source of bioactive metabolites. To investigate the role of these endophytes this research focused on three main objectives: i) Understanding the phylogenetic diversity and distribution of fungal endophytic communities in Cornus florida L.; (ii) Evaluation of the antiproliferative activity of secondary metabolites produced by fungal endophyte Nigrospora sphaerica;; (iii) Evaluation of bacterial endophytes for their plant growth promoting and biocontrol traits; and (iv) Investigating the effect of volatiles produced by selected bacterial endophytes on growth promotion of plants. With the attainment of the four research objectives, this study contributed to the knowledge on indigenous populations of microorganisms that colonize C. florida plants endophytically including their phylogenetic diversity and distribution. Results from this study confirmed that fungal endophytes are diverse in C. florida. (Chapter II). Further results obtained in this study showed that secondary metabolites produced by N. sphaerica inhibited the growth of solid tumors and its migration (Chapter III). This research also contributed to the understanding of mechanism of eight selected bacterial endophytes by providing evidence for their ability to produce secondary metabolites such as hydrolytic enzymes and plant growth promoting properties including phytohormones, siderophore needed in nutrient acquisition, ammonia production and nitrogen fixation affecting plant growth and biocontrol potential against diverse phytopathogens (Chapter IV). Additionally, volatile compounds released from these bacterial endophytes were screened for their abilities to promote growth in Arabidopsis thaliana and tomato plants. Findings from this study revealed ability of bacterial volatiles to modulate root architecture and enhance plant growth (Chapter V). Overall, results suggest endophytes are valuable source of bioactive compounds, possess biocontrol and plant growth promoting abilities