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Teamwork makes the dream work: Co-inoculating microbes to enhance plant growth
By Nikki Burnett – Innovation Project Coordinator
Plants face many abiotic challenges that can impact their growth and reduce yields, including drought, salinity, and nutrient stress, among others. Microbes can help alleviate these different sources of stress, with certain microbes being better equipped than others at providing specific benefits. Inoculating plants with multiple species is called co-inoculation, which is an effective strategy to help alleviate the diverse forms of stress a plant may face. For instance, by inoculating a plant with a microorganism that improves nutrient availability alongside another that enhances drought resistance, the plant can leverage multiple benefits. These effects are often also synergistic – essentially the whole is greater than the sum of its parts!
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A great example of teamwork in nature can be seen in the collaboration between species of rhizobia— nitrogen-fixing bacteria from the genera Rhizobium, Bradyrhizobium, Mesorhizobium, and Sinorhizobium, among others —and certain species of Bacillus. Rhizobia are famous for their symbiotic relationship with leguminous plants, where they capture nitrogen from the atmosphere and convert it into a form that plants can use. To do this effectively, they form root nodules, creating an ideal environment that is rich in energy and low in oxygen, which is crucial for biological nitrogen fixation.
The process of forming these nodules is quite complex, involving a series of signaling events and communication between the plant and the bacteria. However, this intricate process can be disrupted by environmental stresses and nutrient availability. For example, nitrogen fixation requires a lot of energy in the form of ATP (adenosine triphosphate), making phosphorus an essential nutrient. Some Bacillus species excel at converting inaccessible mineral forms of phosphorus into forms that are not only easily taken up by the plant, but also beneficial for their rhizobia partners (1).
Furthermore, certain Bacillus species can produce plant hormones that enhance root growth and increase the surface area for nitrogen-fixing bacteria to establish nodules (2). This partnership leads to greater nodule formation and boosts the activity of the enzyme nitrogenase, which is vital for nitrogen fixation (1–3). The advantages of certain Bacillus species are especially noticeable under stressful conditions, such as drought, high salinity, or temperature extremes, where they can significantly enhance nodulation and improve crop yields (2–5).
Representation of the benefits that certain species of Bacillus can provide under drought conditions. Soybeans co-inoculated with Bradyrhizobium and Bacillus exhibit better nodulation and ultimately healthier plants despite the drought conditions.
Bacillus species aren’t the only ally for nitrogen-fixing rhizobia. Other bacteria such as Pseudomonas and Azospirillum species also contribute to plant health when co-inoculated with rhizobia. Certain species of both partners produce the compounds Indole Acetic Acid (IAA) and ACC deaminase, which are well known to help promote plant growth by influencing hormone levels (2, 4). This helps out rhizobia, because these compounds specifically reduce ethylene, a hormone that can inhibit nodulation, allowing the process to occur more freely (2).
In summary, the teamwork between these different bacterial species not only supports plant health but also enhances the action of each of the beneficial teammates. Teamwork really does make the dream work!
Teamwork also transpires between arbuscular mycorrhizal fungi (AMF) and some species of Bacillus. AMF form symbiotic associations with plants by internally colonizing plant roots, creating a hyphal network, ultimately extending beyond the reach of the root system. This hyphal network benefits the plant by grabbing out-of-reach nutrients and water from the soil. One way to boost this nutrient highway, is to pair certain species of Bacillus – a well-known phosphorus solubilizer with AMF. This team works so well together because particular Bacillus species can convert phosphorus into a form that is readily available to plants, and the AMF assist in transporting it to the plant more quickly (6). Research shows that Bacillus is not just helping with nutrient availability, but also giving AMF a growth boost (7, 8). Bacillus is encouraging the growth of AMF, making it denser and more efficient at collecting and transferring nutrients to the plants. In some cases, specific AMF will release attractive compounds into the soil to actively recruit Bacillus into the rhizosphere to bring about these benefits (8, 9)!
Arbuscular mycorrhizal fungi (AMF) form hyphal extension that go beyond the root system allowing for uptake of nutrients and water beyond where the plant roots can reach. Bacillus species can convert phosphorus into forms the plant can use and the AMF works to more quickly transport it to the plant.
Benefits from the co-inoculation of Bacillus and AMF have been shown on a variety of crops. For example, in rice, the teammates notably improved nitrogen and phosphorus uptake, leading to an increase in shoot dry weight (6). In lettuce, the team demonstrated their ability to not only improve nutrient acquisition, but also enhance plant stress tolerance, significantly improving plant growth under drought conditions (10). The positive effects are observed with certain combinations of Bacillus and AMF – so these interactions are species-specific, and the synergistic activity happens only when the right pair of organisms are co-inoculated together.
A recent study highlighting two compatible species looked at the interactions between Rhizophagus irregularis (AMF) with Bacillus velezensis (8). They showed that B. velezensis colonized the AMF hyphae nearly 5X faster than it can colonize plant roots, and consequently the bacteria were able to colonize the plant more rapidly as well. The AMF acted as a highway for B. velezensis to reach the plant more quickly than if it were moving through the soil on its own. This example highlights the beneficial interactions between AMF and bacteria that boosts the performance of each teammate and ultimately improves the health of the plant.
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Co-inoculating the right pair of microorganisms together presents an effective strategy for enhancing plant health and resilience. By harnessing the synergistic effects of beneficial microbes, we can improve overall plant health and increase the efficiency of each microbe. As we move forward, the integration of these microbial allies into our farming practices will be crucial in addressing the challenges of a changing climate and growing global population.
Lallemand Plant Care’s LALFIX START products combine key nitrogen-fixers Rhizobium leguminosarum, Mesorhizobium ciceri, and Bradyrhizobium elkanii with B. velezensis to harness this beneficial team. Additionally, the combination of LALRISE MAX and LALRISE VITA has shown to be a dynamic duo in improving plant health by combining the actions of AMF and B. velezensis.
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2. F. Bonilha Da Silva, J. Z. Barbosa, T. Tiecher, J. B. M. Borin, B. Treichel, E. L. Saccol De Sá, Species-dependent effect of rhizobacteria co-inoculation in legume plants: A global meta-analysis. Rhizosphere 30, 100869 (2024).
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Published Mar 28, 2025 | Updated Feb 4, 2026