The first research was coordinated by M.Sc. Bernal Matarrita Carranza, from the Organization for Tropical Studies, who developed the Project “Exploration of new associations between social insects and actinomycetes in Costa Rica” as part of his thesis of Master’s in Microbiology at the University of Costa Rica.

The second project, which is also part of the Master’s in Microbiology, is called “Degradation of cellulose in the fungal garden of zompopa ants and vertical vehiculation of associated microorganisms.” This was developed by M.Sc. Rolando Daniel Moreira Soto, professor and researcher at the Microbiology Faculty and researcher at the Center for Research in Tropical Diseases (CIET, its acronym in Spanish). 

These researches had support and participation of Dr. Cameron Currie of the University of Wisconsin, United States of America.

Dr. Adrián Pinto Tomas, professor, Department of Biochemistry of the Medicine School and researcher of the Center for Research in Microscopic Structures (CIEMIC), its acronym in Spanish, was director of both postgraduate thesis. He highlighted the importance of these research projects

According to the expert, studies can confirm the enormous potential of bacteria associated to the insects’ characteristics of Costa Rican biodiversity to solve problems that affect society such as the lack of new antibiotics and efficient strategies to transform vegetable wastes into energy.

In addition, the publication of the results in international journals of high impact demonstrates the quality of the postgraduate studies of the UCR and the research carried out in the country.

Natural Antibiotics

Hymenoptera insects, including ants, bees and wasps, are very susceptible to infections caused by fungi, so they have had to create effective defense mechanisms against pathogens.

As part of these mechanisms, it has been demonstrated the existence of symbiotic associations between these insects and bacteria called actinomycetes, which produce antibiotics naturally.

In this type of associations, bacteria produce secondary metabolites with antimicrobial properties that protect their host (both adult insects and larvae and pupae) or the food sources stored in their nests, such as honey from bees.

Previously, it was believed that zompopas were the only insects that obtained antibiotics from symbionts bacteria, but this work shows that other species of ants, bees and wasps also use this resource.

In this sense, M.Sc. Matarrita and his research group studied new relationships between actinomycetes and 29 different species of hymenoptera insects in La Selva Biological Station of the OET, and other places in the Sarapiquí region in Heredia.

The researchers obtained 150 isolations of actinomycetes, most of them from the genus Streptomyces. In addition, they were able to isolate seven entomopathogenic fungi belonging to the families Ophiocordycipitaceae or Cordycipitaceae, some of which are natural enemies of the insects studied.

Among them, there is a parasite that turns the bullet ants (Paraponera clavata) into a zombie species, manipulating them to leave the nest and look for a high place to die, so that the parasite can leave their bodies to release spores that infect more ants. Subsequently, in vitro cross-bioassays were performed between actinomycetes and parasitic insect fungi, which allowed to identify the presence of inhibitory activity against some of them.

The results obtained provide scientific evidence about new defensive associations between actinomycetes and insects, which in turn represent natural sources of antimicrobial and enzymatic substances with great potential for medical and biotechnological applications.

“We know that there are antifungal substances that inhibit the growth of fungi, but we still need to know what the chemical structure of these substances is to see if it is something new, and if so, if it can be applied for medical purposes. But all this leads to more research”, said M.Sc. Matarrita.

Cellulose Degradation

On the other hand, M.Sc. Moreira and its research group studied the role played by different types of bacteria found in the nests of the Atta and Acromyrmex zompopa ants, coming from different parts of the country, in the degradation of plant material.

Zompopa ants cut and carry fresh leaves and other plant materials to grow a fungus (Leucoagaricus gongylophorus) that serves as food in the underground chambers of the colonies. The structure, called fungal garden, also serves as a refuge for ants and their larvae.

Ant colonies process a large amount of plant material. Each colony consumes the same amount of food as a cow. Recent research has shown that fungal gardens are colonized by symbiotic bacteria that contribute to nitrogen fixation processes and their possible involvement in the degradation of plant biomass has been described.

In this work, UCR researchers used a combination of diverse techniques, including electron microscopy, confocal, microbial cultures, and studies of deoxyribonucleic acid (DNA), to investigate the process of cellulose degradation in fungal gardens and the possible role of the symbiotic bacteria in the process.

The researcher in charge of the study said that the most abundant thing in plants is cellulose (made up of a chain of linked sugars), but it is a molecule that is difficult to break down because it has a type of bond that makes degradation difficult.

The research was able to determine that plant cell walls are visibly degraded in certain regions of the lower section of the fungal garden, where bacteria are more abundant.

This is an important contribution because it was thought that the symbiotic fungus was incapable of degrading the cellulose, limiting itself to penetrate the vegetal tissue through the cuts that the ants make with their jaws.

However, the new evidence shows that there is degradation and that the bacteria associated with the ants contribute to the process.

Thanks to their ability to grow their own food, the zompopa colonies can hold several million working ants, but only one, the queen, is able to lay fertile eggs to generate new insects.

As Moreira explained, in a certain period of the year, the new queen ants (in this case winged ants) propagate this fungus by taking a small fragment of the fungal garden of their parental colony and use it to start a new colony in another place.

According to the researchers, in this fragment, which measures less than 1mm in diameter and is the seed to feed millions of ants, there are more than one million bacteria per gram of fungus.

The researchers obtained evidence that fragments of the fungal garden carried by virgin queens are colonized by a community of bacteria that resembles the main species found in mature fungal gardens, which shows that these bacteria are important for the degradation of the leaves and the operation of the colony of the zompopa ants.

According to the researcher, these results suggest that the beneficial bacteria in the garden are probably transmitted by the new queens to the next generations of ants.

The researcher explained that one of the concerns they had in mind when they proposed the project, five years ago, was the generation of energy from plant material.

Vegetable materials have cellulose and, in our country,, these are very abundant in agriculture and are not always taken advantage of. The idea was to find a way to degrade that material quickly, efficiently and economically to produce biofuels.

“If you really want to get an industrial application of this, you have to analyze the bacteria in terms of cellulose breakdown efficiency, look for bacteria that do it with enough efficiency to use it in industrial processes. If it is found, it would have to be extracted and cultivated in bioreactors to take it to industrial processes”, explained the expert.

For more information, contact Dr. Adrián Pinto at e-mail: adrian.pinto@ucr.ac.cr