Cultivation-dependent transcriptomic reprogramming and insecticidal performance of Beauveria bassiana A1 from solid-state and submerged cultures
This study demonstrates that while solid-state and submerged fermentation induce distinct transcriptomic reprogramming in *Beauveria bassiana* A1, particularly affecting secondary metabolism and extracellular degradation genes, both cultivation methods ultimately yield spores with comparable insecticidal efficacy against *Plutella xylostella* at high concentrations, supporting the potential of submerged fermentation as a scalable alternative for biopesticide production.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
In the world of agriculture, farmers often face a relentless enemy: insects that chew through crops faster than they can be harvested. To fight back without using harsh chemicals, scientists turn to nature's own predators, specifically a microscopic fungus called Beauveria bassiana. This fungus acts like a biological weapon, seeking out insects, landing on them, and growing inside their bodies until the insect dies. The fungus then bursts out, releasing millions of tiny spores to find new victims. For this to work in the real world, farmers need vast quantities of these spores, which means scientists must grow the fungus in large batches.
There are two main ways to grow these fungal armies. The first method, known as solid-state fermentation, is like baking bread in a warm, moist oven. The fungus grows on damp grains or agricultural waste, creating a dry, fluffy layer of spores that are naturally tough and ready to stick to an insect's waxy skin. The second method, submerged fermentation, is more like brewing beer. The fungus grows in a giant tank of liquid, where scientists can precisely control the temperature, oxygen, and nutrients. While the liquid method is easier to scale up and automate, there has been a lingering doubt: does growing the fungus in water change its personality? Does it make the spores less effective at killing insects compared to those grown on solid grains?
A team of researchers at National Taiwan University set out to answer this question by looking not just at how many spores were produced, but at the genetic instructions inside them. They grew the same strain of Beauveria bassiana in both the solid grain environment and the liquid tank. Once the spores were ready, they took a deep dive into the fungus's genetic code to see which genes were turned on or off in each environment. They found that the two groups of fungi were living very different lives. The spores grown on solid grains had switched on a massive array of genes designed for breaking down tough materials. These genes produced powerful enzymes, which are biological tools that act like molecular scissors, capable of slicing through the hard outer shell of an insect. They also activated genes for creating secondary chemicals, which help the fungus compete and defend itself.
In contrast, the spores grown in the liquid tank had a different set of priorities. Their genetic activity was focused on finding and absorbing iron, a nutrient that is often scarce in liquid environments, and on producing specific toxins. They did not turn on the same heavy-duty cutting tools that the solid-grown spores did. This suggested that the liquid-grown spores were not as prepped for the immediate task of chewing through an insect's armor. The researchers then tested this theory by spraying both types of spores onto larvae of the diamondback moth, a common pest that damages vegetables. They used different concentrations, from a low amount to a very high amount of spores.
The results showed a clear difference in timing, but not in the final outcome. When the researchers used a moderate amount of spores, the ones grown on solid grains killed the insects slightly faster. The larvae died sooner because the solid-grown spores were genetically primed to attack the insect's shell immediately upon contact. The liquid-grown spores took a little longer to get started, likely because they had to ramp up their own cutting tools after landing on the insect. However, when the researchers used a high concentration of spores, the difference vanished. At this high dose, both types of spores killed all the insects within three days. The sheer number of attackers overwhelmed the insects regardless of whether the spores were genetically prepped for immediate action or not.
This discovery suggests that the liquid method of growing the fungus is a viable alternative for making biopesticides, provided the application strategy is adjusted. While the solid-grown spores might have a head start in speed, the liquid-grown spores are just as deadly if enough of them are applied. The study indicates that the genetic differences caused by the growing environment change the speed of the attack rather than the ultimate success of the mission. For farmers and manufacturers, this means that the easier, more controllable liquid method can be used to produce these biological controls, as long as they ensure a high enough density of spores is delivered to the crop to compensate for the slightly slower start. The fungus remains a powerful tool, and its effectiveness depends less on where it was born and more on how many of them are sent to the battlefield.
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