BY ADELINE TING
BELIEVE it or not, there is something growing in our plants! Inside the tissue of roots, stems, leaves, flowers and seeds, we can find tiny living microscopic organisms (microbes) known as endophytes. Endophytes, as the name suggests, refers to “internal or within” (endo) and “plants” (phyta). Therefore, endophytes can be bacteria or fungi that is found living inside the plants. And amazingly, although endophytes are present in plants, they do not make the plants sick. This is similar to humans having good bacteria in our gut system. It has been estimated that every plant on earth host endophytes within them, speculating that at least 1 million endophytes may exist on earth!
What do they do?
Historically, the first few studies were on endophytes in grasses grazed by cattle. Some of the cattle experience poisoning due to the alkaloids produced by the endophytes in the grasses. So in their own way, endophytes help to protect plants from herbivore grazing.
There have also been studies where endophytes aid in plant survival and growth. In orchids for example, endophytes help in seed germination. In other plants, endophytes produce hormones and vitamins that help plants to grow. This can benefit important crops such as oil palm and banana, as discovered by researchers from the Applied Microbiology Research Group (or the ATSY group) from Monash Malaysia. In their study, five fungal endophytes were introduced to oil palm seedlings, and they showed increased height, weight, root growth and stem circumference compared to those without endophytes. Better plant growth was also due to better nutrient and water uptake.
The ATSY group further discovered that two of the endophytes showed ability to improve survival of oil palm seedlings when infected with the Basal Stem Rot disease. Disease incidence of oil palm seedlings after four months was 67% for seedlings with endophytes, compared to 100% in seedlings without endophytes. The study showed that endophytes improved plant survival when plants are grown in disease-infested soils, as well as in environments that experience drought, heat and poor nutrient levels.
In addition, endophytes may produce similar beneficial compounds as their plants. This is due to their long co-existence within the plants and adaptations to produce similar chemical compounds. One good example is the production of taxol, an antitumour agent from the endophyte found in the Pacific yew tree (Taxus brevifolia). Both endophyte and yew tree produce similar effective anticancer compounds. However, the endophyte is favoured as taxol can be produced from fermentation of endophyte, rather than from harvesting of the trees. Endophytes are also capable of producing other compounds (e.g., pigments, hormones, vitamins, enzymes), which has various applications.
The ATSY group also explores the production of beneficial compounds by endophytes. In one study, 89 endophytes were found from four Malaysian medicinal plants, and 25 of the endophytes produced the L-asparaginase enzyme, critical for the treatment of acute lymphoblastic leukemia cells. The group also investigated the manipulation of light spectrum on pigment and compound production. This technology will aid in growing endophytes and optimizing production of beneficial compounds in the lab, which is so much easier and faster than growing and harvesting the plant.
The ATSY group also discovered that endophytes from plants, especially from the phytoremediator plant (Phragmites sp.), showed tolerance to high metal concentrations. All 21 endophytes from Phragmites were able to show tolerance to cadmium, copper, zinc, chromium and lead. Three of the endophytes were further developed into powder-like biosorbents to remove dye and metal pollutants from water.
How do they benefit mankind?
From their natural endophyte-host relationship, researchers discovered that endophytes have the potential for development to replace chemical fertilizers and pesticides. Endophytes can be removed from within the plant tissues, grown in the lab, developed and re-introduce to plants as how fertilizers and pesticides are applied. They can also be grown in the lab independent from plants, to produce valuable compounds that have many applications. Up-scaling of endophyte production via fermentation technology is also more economical and practical compared to growing plants. The tiny microbes that live in plants are therefore capable of presenting greener and more sustainable solutions.
What is the future of endophytes?
The potential for endophyte use is infinite. In recent times, researchers continued to discover their broad range of use, to produce compounds that are antimicrobial, antioxidant, antitumour, as well as pigments and enzymes that can be useful. With these discoveries, the humble microbes living in the plants are not just ecologically important through their natural roles and association with plants, but have now become sustainable sources for novel compounds for biomedical, industrial and even for bioremediation applications.
NOTE: The author for this article leads the ATSY group from School of Science at Monash University Malaysia. She has recently written a book “Endophytes of the Tropics: Diversity, Ubiquity and Applications” published by CRC Press. She is also the current Topic Editor for the Research Topic: Endophytes and Their Biotechnological Applications with Frontiers in Bioengineering and Biotechnology.