-By Kranti Karande
A large number of micro-organisms are present in the soil ecosystem. There is a popular phrase that, microbes in a handful of soil are more in number compared to the total number of human beings that have ever existed on this planet. Soil life consists of microbes, nematodes, earthworms, ants, other insects, etc. With an estimated 100 billion bacteria that can be found in a handful of soil, it is the largest group of organism in this life-sustaining ecosystem. It is an astonishing reality that this handful of soil contains about 500 individual species of fungi and its mycelium can run up to 50 km in length. Staggering, isn’t it!
Among microbes, bacteria are present in large number in soil. Soil bacteria are mainly responsible for nitrogen fixation. Actinomyecetes, a group of bacteria break large lignin molecules into small molecules. Although not as commonly abundant as bacteria, fungi also significantly contribute in soil health by decomposing organic matter and nutrient recycling. Microbes contribute to soil in various ways by increasing its fertility, aggregation ability and by fixing nitrogen.
Soil ecosystem plays an important role in cultivating high yielding crops. Microbes being the major community of the soil, it is important to study them in order to conserve and nurture soil ecosystem. Studying soil microbes will help in increasing soil fertility and indirectly will contribute for betterment of farmers’ lives and for betterment of society.
Isn’t it interesting to study how these tiny microbes contribute in overall plant health? The very first interaction between plants and microorganisms occurs in soil. Every plant is associated with a unique rhizosphere (root microbial community). The rhizosphere microbial community is selected from large number of microorganisms present in the soil. The symbiotic association (beneficial for both) between rhizosphere and plant leads to complex interactions contributing to plant growth.
The interactions between these three components: plants, microbes and soil system play a critical role in maintaining health of the plant. However, the complexity of these interactions is not yet clear. Research group led by Dr. Kamlesh Jangid at NCMR, NCCS Pune is trying to understand this complex interaction.
Animals call for help when in need, but can you imagine how bacteria might be communicating with each other, especially in the complex soil ecosystem? You may wonder whether they use mobile phones. Not really, but they do have a very advanced communication system. Bacteria produce and release signalling molecules called as Auto inducers (AIs), which are then sensed by neighbouring organisms enabling them to differentiate between self and non-self. Isn’t it fascinating? This mechanism of cell-to-cell communication is known as quorum sensing.
While the mechanism was first discovered in 1970s by the team of Kenneth Nealson, Terry Platt and J. Woodland Hastings, it was not until 1994 that the term “quorum” was associated with this density-dependant mechanism by Fuqua , Winans and Greenberg. Quorum is a mechanism by which bacteria plan and fine-tune their actions as a group rather than as individual cells, thus co-ordinating gene expression and overall microbial population behaviour. Dr. Jangid’s group is discovering the presence of this mechanism across the bacterial community in soils. Studying this mechanism will help the scientific community to better understand the gene regulation in the soil microbes and will answer the questions related to their functional roles.
While studying the most abundant bacteria in soil, affiliated with the phylum Actinobacteria, Dr. Jangid’s group discovered that quorum sensing is extremely under explored partly due to the lack of sensor systems that can detect the huge diversity of AI molecules secreted by this group of bacteria. Specifically, only nine out of the 342 genera in the phylum Actinobacteria are experimentally proven to have this communication mechanism. Dr. Jangid’s group is now developing sensor systems for detecting signalling molecules produced by these bacteria to better understand quorum sensing in this phylum. This research can likely contribute to agricultural, biotechnological, medical and ecological fields.
If we understand the distribution of quorum sensing in soil bacteria, we will be able to modulate soil communities to enhance soil health and increase overall crop productivity. In addition, this will facilitate our understanding of the communication between microbes present in the rhizosphere and why plants are associated with a unique rhizosphere (root microbial community).
It was a great pleasure to interact with Dr. Jangid. In the discussion, Dr. Jangid commented that, “Soil microbiology and bacterial quorum sensing are two separately followed niche fields and their interjection enables us to explore new paths for improving soil health and creating more sustainable agricultural practices. Quorum sensing is also being researched extensively for developing new synthetic analogues that block (or quench) this communication mechanism among pathogenic microbes rather than the conventional anti-microbial drugs in use. The advantage of quorum quenching is that unlike antimicrobial targets, we expect very little to none resurgence towards this approach”.
Link to Dr. Jangid’s lab webpage: https://microbial-lab.org/