Non-pathogenic Oomycetes as an untapped source of β-glucan: yield, structure, and bioactivity across Pythium and Phytopythium isolates from Thailand

In the microscopic world of soil and decaying plant matter, a vast array of organisms live that are often mistaken for fungi but belong to a completely different biological family. These are the oomycetes, water molds that play critical roles in ecosystems, sometimes as harmless decomposers and other times as devastating plant pathogens. While scientists have long studied the cell walls of true fungi, which are built from a tough material called chitin, the cell walls of oomycetes are constructed differently. They are rich in a specific type of sugar chain known as beta-glucan. This substance is not just a structural brick; it is a molecule with a history of use in human health, known for its ability to support the immune system and act as an antioxidant. For decades, the search for these beneficial molecules has focused on familiar sources like oats, mushrooms, and baker's yeast. However, a significant gap remained in our knowledge: while the cell walls of a few dangerous, disease-causing oomycetes were known to contain these sugars, no one had systematically looked at the thousands of harmless or weakly harmful species to see if they could be a rich, untapped source of this valuable material.

A team of researchers in Thailand set out to fill this gap by turning their attention to a collection of non-pathogenic oomycetes they had previously gathered from rivers, waterfalls, and forests. Instead of looking for disease, they looked for sugar. They selected eleven different strains of these organisms, specifically from the Pythium and Phytopythium groups, which are generally considered safe for plants. The goal was simple yet ambitious: to see if these harmless microbes could produce beta-glucan in large quantities, to understand the exact shape of the sugar chains they made, and to test if these extracts could offer any biological benefits, such as fighting bacteria or helping plants defend themselves. The researchers grew these microbes in various liquid foods, carefully adjusting the amount of sugar added to the mix to see how it influenced production. They then harvested the fungal-like threads, dried them, and used a series of chemical washes to isolate the cell wall material, leaving behind everything else to reveal the pure beta-glucan.

The results were striking. Under standard growing conditions, these non-pathogenic strains produced beta-glucan content ranging from about 24 percent to nearly 33 percent of their dry weight. This was already a strong performance, surpassing the amounts found in the dangerous, disease-causing relative Pythium insidiosum and rivaling the beta-glucan levels found in commercial baker's yeast, which is currently a major industrial source. However, the researchers discovered that the environment mattered immensely. When they added a specific amount of glucose to the growth medium, one particular strain, identified as Pythium catenulatum CHS-10, responded with a dramatic surge in production. Its beta-glucan content jumped to nearly 64 percent of its total weight, a yield that far exceeded the commercial yeast reference and any other strain tested. This suggested that these harmless organisms are not just capable of making the substance, but that they can be coaxed into becoming highly efficient factories for it.

To ensure that what they had found was indeed the right kind of sugar, the team analyzed the molecular structure of the extracts. Using advanced spectroscopy, which measures how molecules absorb light and vibrate, they confirmed that the sugar chains from all eleven strains shared a consistent architectural blueprint. The molecules possessed a specific backbone structure with side branches, a pattern previously documented only in the pathogenic species but now confirmed to be a standard feature across these harmless relatives. This structural consistency is important because the specific shape of the sugar chain is what allows it to interact with living systems. The fact that these non-pathogenic strains shared the same structural signature as their dangerous cousins meant they possessed the same fundamental potential to act as biological signals.

The researchers then moved on to test what these extracts could actually do. They placed the beta-glucan on small discs and set them against various bacteria and fungi to see if the sugar could inhibit growth. The extracts showed a selective ability to slow down certain harmful bacteria, including those that cause wilt in tomatoes and blight in rice, without affecting the harmless yeast used as a control. This selectivity suggests the sugar might interact specifically with the cell walls of certain bacteria. In tests measuring antioxidant activity, which gauges a substance's ability to neutralize harmful free radicals, several of the extracts performed exceptionally well, matching or approaching the performance of a standard antioxidant compound. Perhaps most intriguingly, when the researchers applied the beta-glucan solution to young durian seedlings, the plants responded by producing a natural defense chemical called scopoletin. This reaction, known as a phytoelicitor effect, indicates that the sugar chains from these harmless microbes can trick a plant into thinking it is under attack, prompting it to strengthen its own defenses without the plant actually getting sick.

While these findings are promising, the study was designed as a first step to identify potential rather than to provide a final, industrial-grade solution. The researchers noted that to fully understand the material, future work would need to determine the exact size of the sugar molecules and confirm the precise connections between the sugar units using more detailed imaging techniques. They also emphasized that the antibacterial and antioxidant effects observed here were preliminary screens, and that the specific doses required for real-world agricultural or health applications would need to be determined through further testing. Nevertheless, the study successfully established that non-pathogenic oomycetes are a quantitatively competitive and previously overlooked source of beta-glucan. By identifying specific strains that can be grown to high yields and confirming their structural and biological potential, the work opens a new door for developing sustainable, locally sourced bioactive materials from organisms that have long been ignored in the search for beneficial sugars.