Scientists from the National Laboratory of Biorenewables of the National Center for Research in Energy and Materials (LNBR-CNPEM) took another step towards understanding how fungi of the species Aspergillus niger and Trichoderma reesei produce the enzymes used in the process of degradation of sugarcane bagasse. sugarcane and other biomass -- something essential for the production of second-generation bioethanol.

The study was published in the journal Frontiers in Fungal Biology.

"We studied two of the fungal species most used to produce several industrial enzymes. Trichoderma reesei is the most important for the production of cellulase, while Aspergillus niger produces citric acid and other important enzymes for various applications in the chemical industry", says Gustavo Pagotto Borin, who carried out the study during her doctorate at LNBR-CNPEM with a grant from FAPESP.

Currently, imported enzymatic cocktails are used to degrade sugarcane bagasse. The process is necessary for the production of so-called second-generation ethanol, which is more complex to obtain than first-generation ethanol, made from sugarcane juice. Today, these inputs are responsible for around 50% of the cost of second-generation ethanol in Brazil.

Understanding how these enzymes are produced by microorganisms can help increase the efficiency of the process, in addition to paving the way for the development of domestic products, specific to our biomass and cheaper.

"This type of research has advanced a lot in recent years and companies are investing a lot in the so-called biorefineries. They can produce both first and second generation ethanol and other products from sugarcane biomass, replacing oil and contributing to a low-carbon economy", says Juliana Velasco de Castro Oliveira, a researcher at LNBR-CNPEM supported by FAPESP and coordinator of the study.

Power supply

In the study, the researchers used the metabolomics technique to understand what the fungus metabolism produces when it has sugarcane bagasse as a carbon source. For these microorganisms, carbon is like food, a source of resources to grow and follow their life cycle.

The metabolism of fungi with other carbon sources was also analyzed. In this case, lactose, glucose and carboxymethylcellulose (CMC), three types of sugar widely used in industry and which can also be used as "food" for fungi that produce enzymes of interest. The researchers' idea with this was to verify how much these carbon sources of different levels of complexity can alter the fungal metabolism.

A set of metabolites (products of metabolism) was found in both fungi, in all four carbon sources: the sugars trehalose and mannitol, in addition to the amino acids glutamate, glutamine and alanine.

"These five molecules seem to be extremely important for the two fungi. Since they are present in both species, it is possible that they have been conserved throughout evolution", says Borin.

Glutamine, among other functions, is related to the recycling of nitrogen within the cell. Its importance is also due to its participation in the TOR cellular signaling pathway, which is essential for growth and other essential functions of the cell.

A surprise for the researchers was having found metabolites that suggest cell stress, such as the one known by the acronym GABA and glycerol. "It was an interesting finding. Despite being very efficient in the degradation of biomass, it is possible that these fungi have not yet reached their full potential. If this is confirmed in the future, it would be interesting to think about genetic modifications that favor and make these processes more efficient , with a greater production of enzymes", concludes Oliveira.

In previous years, since Borin's master's degree, the researchers had analyzed the same species of fungus using sugarcane bagasse as a carbon source using other so-called "omics" techniques.

Secretomics (which analyzes the proteins that are secreted by cells) and transcriptomics (which studies the genes that are being transcribed and analyzes co-expression networks) were used and, in this case, still unknown genes were identified that may be linked to the degradation of bagasse in Trichoderma reesei.

The study published now closes a cycle that increases understanding of how these fungi produce important enzymes to transform sugarcane bagasse into other products.

The article Assessing the intracellular primary metabolic profile of Trichoderma reesei and Aspergillus niger grown on different carbon sources is available by clicking here.