Medicinal Plants: Microbial Interactions, Molecular Techniques and Therapeutic Trends

Changing climatic conditions, biotic and abiotic stresses along with use of
synthetic fertilizers have deteriorated soil quality and crop yield. Microorganisms are
natural inhabitants of soil and plant surfaces that form a stable dynamic system with the
host plants. The plant microbiome assists in plant growth by solubilizing minerals,
recycling nutrients and inducing defense responses by mitigating environmental
stresses. These plant-associated microorganisms can be used as functional moieties to
enhance overall plant productivity and reduce negative impacts on the ecosystem. The
plants and microbes are contemplated as natural partners that harmonize various
functional traits, however, the magnitude of friendly or hostile consortium depends on
the kind of microorganisms involved. Before the scientific advent of advanced
technologies, conventional approaches such as culturing on media, microscopic
observations and biochemical tests provided awareness of how these two communicate.
Later on, contemporary molecular-based tools like polymerase chain reaction (PCR),
microarrays, enzyme-linked assays (ELISA), and nucleic acid-based methods (nextgeneration
sequencing, etc.) surfaced. This chapter will comprehend different types of
aboveground and subsurface microbes associated with the plants, their impact on
sustainable agriculture and high-throughput technologies used to investigate the plantmicrobe
relationship.

This chapter highlights the significance of microbiomes especially plant
microbiomes in the field of therapeutics. The Plant microbiome comprises epiphytes
and endophytes inhabiting the surface as well as inside of the tissues of the host. These
microbial communities occupy a well-defined habitat and perform various activities
developing certain interactions with the host such as commensalism, mutualism, and
parasitism. For the establishment and functioning of the plant microbiome, plant root
releases exudate according to the nutritional requirement of particular microbial
species. In response to the stimulus, microbes chemotactically move towards the roots,
colonize and move to other parts of the plant. Microbes also adopt certain mechanisms
not only to colonize and multiply in specific hosts but also to promote the growth of the
host by secreting various plant growth hormones and exopolysaccharides. The
numerous compounds produced by microbes make plants tolerant of biotic and abiotic
stresses. The microbial communities in plant microbiome have an active role in
maintaining the health, ecology and physiology of the host. As a major portion of the
world’s population is dependent on phytotherapeutic medicines according to the World
Health Organization, the pharmacological characteristics of major medicinal plants
such as Aesculus hippocastanum and Ginkgo biloba are described in detail. This
chapter highlights the significance of the core role of the microbiome associated with
plants in the synthesis of various medicinal compounds. The phytotherapeutic potential
of plant microbiome revealed that endophytes and epiphytes isolated from various plant
species showed great potential for the production of antimicrobial as well as antiinflammatory
substances. The medicinally rich compounds such as antibacterial
proteins, phenols, saponin glycosides, flavonoids, terpenoids, carbohydrates and fatty
acids isolated from plant-associated microbes have various applications in the
treatment of fetal diseases and also exhibit anti-inflammatory action. Certain public
concerns are raised about the side effects of medicinal plants used in phytotherapeutics.
A relevant case study about public concerns along with preventative measures such as
rigorous testing is provided in this chapter.

Regulation of biogeochemical cycles depends on soil micro biota in which
numerous and distinct types of bacteria are involved. These bacteria share a common
environment in the soil and interact with the plants at three different levels i.e.
endosphere, phyllosphere, and rhizosphere, resulting in improved soil fertility and plant
health. The study of medicinal plants is ignored in Pakistan, though there exists a large
number of different avenues for research in this field. Studying the medicinal plantbacteria
relationships in the era of new-generation sequencing paves new ways for
understanding their association and facilitates improvement in sustainable production.
Answers to new queries like “How bacteria respond to climatic changes” and “How do
they interact with one another and with medicinal plants for growth and development”
along with the exploration of rhizospheric bacteria in the future for enhancement in the
production of secondary metabolites in medicinal plants might be a new vista unlocked
for the sustainable agricultural practices. In this chapter, we focused on the role of soil
bacteria-medicinal plants interaction in growth, nutrient acquisition, environmental
stress alleviation, and quantity and quality of medicinal compounds present in these
plants.

Medicinal plants are a natural source of therapeutic compounds and
secondary metabolites; therefore, their demand is increasing day by day. Since the last
thirty decades, their cultivation as well as preservation with the help of biofertilizers or
pesticides is a point of great concern. The rhizosphere is an important area around the
roots. It is a habitat for many kinds of microorganisms like fungi. This soil microbial
performs a variety of beneficial functions for the growth of plants such as nitrogen
fixation, solubilization and removal of toxins. Endophytes are also an important class
of microbial flora that helps in the absorption of water and nutrients for the plant.
Additionally, they also make plants able to cope with environmental stresses. Fungal
endophytes supervise photosynthesis. Certain therapeutically important plants
including licorice and white ginger lily can also perform antimicrobial activity
depending upon the endophytic composition they have. These types of plants having
antimicrobial activity are of great significance as they act as eco-friendly biopesticides.

Plants and microorganisms have long evolved together and our most recent
discoveries using advanced techniques have allowed us to understand the chemical
interface within the plant further explaining the relationship between them. As we
discover the interaction between the plants and the associated microorganisms, it has
been clearer to us that there has been a synergy more evident than that of antagonism
among them. A lot of chemicals or metabolites are being released favouring both the
host as well as the microbes during this contact. Such an interaction which leads to the
release of certain metabolites can be managed and manipulated in bringing about
positive effects for the biosphere and environment. One instance of this positive effect
can be the use of medicinal plants and their microbe-facilitated associated metabolites
which may be regulated through the application of different endophytic
microorganisms. If we can control the release of different metabolites from plants
particularly from those of medicinal plants, we can harvest significant benefits for
human and animal health as we are utilizing endophytes for their role as biofertilizers.
The food for medicine concept has been emerging and requires quick and efficient
identification of metabolites as well as chemicals that may be used in addressing
multiple diseases in human beings and other animals.

Probiotics are microorganisms, when consumed, give health benefits due to
improvement in the activity of gut microflora. Various health claims are associated
with probiotics e.g. modulation of the immune system, mitigation of lactose
intolerance, protection from infections and maintenance of healthy gut microflora.
They have also been demonstrated to be helpful in treating a wide range of illnesses,
including cancer, inflammatory bowel syndrome, diarrhea brought on by antibiotics,
and infantile diarrhea. Streptococcus, Bacillus, Enterococcus, Escherichia coli,
Bifidobacterium, Lactobacillus, and several strains of the fungus Saccharomyces are
significant probiotic bacterial genera. In fibrous parts of plants and probiotic bacteria,
the bacteriocins play a major synergistic antimicrobial role. Prebiotics are nondigestible
plant materials i.e., complex carbohydrates, fermented in the colon, thus
yield short chain fatty acids and energy, and enhance the growth of probiotics. Inulin
and fructans are important plant prebiotics. The indirect health benefits of prebiotics
are immunomodulatory characteristics, mineral absorption, cancer prevention, and
modulation of the metabolism of gut flora, and the prevention of constipation and
diarrhea. Many fruits, tuber crops, root crops as well as vegetables contain a huge
reservoir of prebiotic carbohydrates. The function of probiotic microbes in foods
includes modulation of the immune system, normalization of gastrointestinal activity,
and the inhibition of the growth of pathogenic microbes and harmful metabolites. The
function of prebiotic food material is to promote the growth of healthy bacteria in the
intestinal tract. This chapter highlights the potential need of probiotics and prebiotics in
our diet, and it also discusses their health benefits, mode of action, sources, food
applications, distinct types, and future perspectives.

Medicinal plants provide a substantial source of bioactive compounds which
serve greatly in the pharmaceutical industry. Before revolutionary advancements in
medicines, traditional biotechnology approaches have been used in the breeding of
significant therapeutic plants. The challenge is to incorporate effective, efficient, and
resilient breeding techniques to enhance the production of phytochemicals by
medicinal plants. Genetics and biotechnology can aid in the rapid advancement of
therapeutic plants by assessing genetic diversity, conservation, proliferation, and
overproduction. Hence, the use of advanced technologies is crucial for selecting,
multiplying, and preserving medicinal plants.