Growth-related, antifungal and metal-binding activities of Penicillium janthinellum Z1-1031

In the hidden world beneath the soil, plants do not grow alone. They exist in a bustling neighborhood of microscopic life, where fungi and bacteria constantly interact with root systems. Some of these tiny neighbors are helpful, acting as guardians against disease or helping the plant absorb nutrients, while others are harmful invaders that can rot the roots and kill the crop. For farmers and scientists, understanding which microscopic allies are worth inviting into this underground community is a major challenge. This is especially true for the Panax notoginseng plant, a highly valued medicinal herb used for centuries to treat heart and blood conditions. Its roots are packed with valuable compounds, but the plant is notoriously difficult to grow because it is easily attacked by soil-borne diseases and can accumulate dangerous heavy metals from contaminated earth. Researchers are constantly looking for natural ways to protect these plants and improve their quality without relying on harsh chemicals.

A team of scientists at Shenyang Pharmaceutical University recently turned their attention to a specific fungus they had previously found living on the roots of healthy Panax notoginseng plants in China. This fungus, identified as Penicillium janthinellum, was not just a passive resident; the researchers wanted to know if it could actively help the plant survive and thrive. They set out to test three specific abilities: whether the fungus could grow alongside the plant without hurting it, whether it produced substances that could kill harmful fungi, and whether it could interact with toxic metals in the soil. Their goal was to see if a single microscopic organism could act as a multi-purpose partner for the medicinal plant, offering protection, growth support, and environmental cleanup all at once.

The researchers began by growing the fungus in a laboratory setting to see what chemicals it produced. They discovered that the fungus made a significant amount of a substance called brefeldin A. When they tested this purified chemical against Fusarium solani, a notorious fungus that causes root rot in Panax notoginseng, they found it was a powerful inhibitor. The chemical stopped the harmful fungus from growing, and the more of it they added, the stronger the effect became. However, the team was careful to check if this same chemical might hurt the plant it was supposed to help. When they exposed the tips of the plant's roots to low concentrations of the chemical, the cells remained healthy with no significant damage to their outer membranes. Only when the concentration was raised to very high levels did the chemical begin to harm the plant cells. This suggested that the chemical could potentially fight disease without injuring the host, provided the amounts remained low.

To see how this played out in a real-world setting, the scientists moved their experiments to a greenhouse. They planted Panax notoginseng in soil and introduced the fungus to the area surrounding the roots. They tracked the fungus over time using a special glowing tag that allowed them to see if it was still alive and present in the soil. The fungus proved to be a persistent resident, remaining detectable in the soil for at least 56 days after it was introduced. During this time, the researchers also found traces of the protective chemical, brefeldin A, in the soil, confirming that the fungus was actively producing it right where the plant roots were growing.

The results for the plants themselves were encouraging. The Panax notoginseng plants that grew with the fungus survived at higher rates and grew larger than those in the control group. After four months, the plants treated with the fungus had significantly more root weight, which is crucial for a medicinal crop where the roots are the valuable part. The researchers also measured the levels of antioxidant enzymes in the plant roots, which act as a defense system against stress. Plants treated with the fungus showed much higher levels of these protective enzymes, suggesting the fungus helped the plant stay healthy and resilient. Interestingly, the fungus also caused a temporary spike in the amount of a specific medicinal compound called ginsenoside Rg1 during the early stages of growth, though this effect faded over time.

Beyond helping the plant grow, the fungus showed a surprising ability to interact with heavy metals. In laboratory tests, the fungus was able to bind to toxic metals like cadmium, copper, lead, and arsenic, effectively pulling them out of the liquid solution. It also had the ability to change the chemical form of arsenic, converting one type into another. When the scientists applied the fungus to the greenhouse soil, the levels of these metals measured in the dirt were lower than in the untreated soil after one and four months. This suggests the fungus might be helping to reduce the amount of toxic metals available in the soil environment.

Despite these promising findings, the researchers were careful not to claim that the problem was completely solved. They noted that while the fungus produced a chemical that killed harmful fungi in a test tube, they did not prove that it stopped root rot in the actual greenhouse plants. They also pointed out that changing the form of arsenic does not necessarily mean the metal is less dangerous, as the new form can sometimes be more toxic or mobile. Furthermore, they emphasized that the safety of the protective chemical for human consumption had not been fully tested. The study successfully identified a fungus with multiple useful traits—promoting growth, producing antifungal chemicals, and interacting with metals—but the team concluded that more research is needed to confirm its safety and effectiveness before it can be used as a standard tool for farming this valuable medicinal plant.