Endophytes: a potential resource for biosynthesis, biotransformation, and biodegradation

In natural ecosystems, endophytes, which live in the inner tissues of healthy plants, exhibit complex interactions with their hosts. During a long coevolutionary process with their hosts, endophytes have developed many significant and novel characteristics. In order to maintain a stable symbiosis, endophytes secrete varieties of extracellular enzymes that contribute to colonization and growth. All these specific enzymes, under certain conditions, could be exploited. Nowadays, more and more complex chemical reactions are being replaced by moderate and pollution-free enzymatic reactions. Bacteria have been widely used in bioengineering, but endophytes, as a kind of organism, have not been fully developed. Therefore, great efforts to develop endophyte resources could bring us a variety of benefits, such as novel and effective bioactive compounds that cannot be synthesized by chemical reactions. It is noteworthy that, after long-term coexistence with hosts, endophytes can synthesize biologically active substances similar to the secondary metabolites produced by host plants. This could help us to accumulate many valuable drug compounds such as paclitaxel and camptothecin in a short time period. In addition, endophytes are widespread in plant roots; they can deeply affect soil chemical composition, micro-ecosystems, and physical structure over their life cycle. Besides that, endophytes play an important role in the degradation of plant litter and organic pollutants, which have an active effect on the improvement of soil fertility. Endophytes are a most promising microbial resource, waiting to be exploited.