A complex metabolic network and its biomarkers regulate laccase production in white-rot fungus Cerrena unicolor 87613.

BACKGROUND: White-rot fungi are known to naturally produce high quantities of laccase, which exhibit commendable stability and catalytic efficiency. However, their laccase production does not meet the demands for industrial-scale applications. To address this limitation, it is crucial to optimize the conditions for laccase production. However, the regulatory mechanisms underlying different conditions remain unclear. This knowledge gap hinders the cost-effective application of laccases. RESULTS: In this study, we utilized transcriptomic and metabolomic data to investigate a promising laccase producer, Cerrena unicolor 87613, cultivated with fructose as the carbon source. Our comprehensive analysis of differentially expressed genes (DEGs) and differentially abundant metabolites (DAMs) aimed to identify changes in cellular processes that could affect laccase production. As a result, we discovered a complex metabolic network primarily involving carbon metabolism and amino acid metabolism, which exhibited contrasting changes between transcription and metabolic patterns. Within this network, we identified five biomarkers, including succinate, serine, methionine, glutamate and reduced glutathione, that played crucial roles in co-determining laccase production levels. CONCLUSIONS: Our study proposed a complex metabolic network and identified key biomarkers that determine the production level of laccase in the commercially promising Cerrena unicolor 87613. These findings not only shed light on the regulatory mechanisms of carbon sources in laccase production, but also provide a theoretical foundation for enhancing laccase production through strategic reprogramming of metabolic pathways, especially related to the citrate cycle and specific amino acid metabolism.

N-acetylglucosamine kinase (BbHxk1) has pleiotropic effects on vegetative growth, cell wall integrity, morphological transition, cuticle infection, and metabolic modulation in the biological pesticide Beauveria bassiana.

Beauveria bassiana is a popular and eco-friendly biopesticide. During its pathogen-pest interaction, both N-acetylglucosamine (GlcNAc) catabolism and anabolism are crucial for nutrient supply and cell-wall construction. The initiation of GlcNAc metabolism relies on the catalysis of GlcNAc kinase, which has been extensively studied in the human pathogen Candida albicans. However, the physiological function of GlcNAc kinase remains poorly understood in entomopathogenic fungi. In the present study, a GlcNAc kinase homolog was identified and designated as BbHxk1 in B. bassiana. Deletion of BbHxk1 resulted in viable but reduced vegetative growth on various carbon sources. ΔBbHxk1 mutants displayed severe defects in cell wall integrity, making them more susceptible to cell wall stress cues. Furthermore, the absence of BbHxk1 resulted in an increase in conidial yield and blastospore production, and a faster rate of germination and filamentation, potentially attributed to higher intracellular ATP levels. BbHxk1 deficiency led to a reduction in the activities of cuticle-degrading enzymes, which might contribute to the attenuated pathogenicity specifically through cuticle penetration rather than hemocoel infection towards Galleria mellonella larvae. Being different from C. albicans Hxk1, which facultatively acts as a catalyzing enzyme and transcriptional regulator, BbHxk1 primarily acts as a catalyzing enzyme and metabolic regulator. The altered metabolomic profiling correlated with the phenotypic defects in ΔBbHxk1 mutants, further implicating a potential metabolism-dependent mechanism of BbHxk1 in mediating physiologies of B. bassiana. These findings not only unveil a novel role for GlcNAc kinase in B. bassiana, but also provide a solid theoretical basis to guide metabolic reprogramming in order to maintain or even enhance the efficiency of fungi for practical applications.

Transcriptomic and metabolomic analysis unveils a negative effect of glutathione metabolism on laccase activity in Cerrena unicolor 87613.

The white rot fungus Cerrena unicolor 87613 has been previously shown to be a promising resource in laccase production, an enzyme with significant biotechnological applications. Conventional methods face technical challenges in improving laccase activity. Attempts are still being made to develop novel approaches for further enhancing laccase activity. This study aimed to understand the regulation of laccase activity in C. unicolor 87613 for a better exploration of the novel approach. Transcriptomic and metabolomic analyses were performed to identify key genes and metabolites involved in extracellular laccase activity. The findings indicated a strong correlation between the glutathione metabolism pathway and laccase activity. Subsequently, experimental verifications were conducted by manipulating the pathway using chemical approaches. The additive reduced glutathione (GSH) dose-dependently repressed laccase activity, while the GSH inhibitors (APR-246) and reactive oxygen species (ROS) inducer (H2O2) enhanced laccase activity. Changes in GSH levels could determine the intracellular redox homeostasis in interaction with ROS and partially affect the expression level of laccase genes in C. unicolor 87613 in turn. In addition, GSH synthetase was found to mediate GSH abundance in a feedback loop. This study suggests that laccase activity is negatively influenced by GSH metabolism and provides a theoretical basis for a novel strategy to enhance laccase activity by reprogramming glutathione metabolism at a specific cultivation stage.IMPORTANCEThe production of laccase activity is limited by various conventional approaches, such as heterologous expression, strain screening, and optimization of incubation conditions. There is an urgent need for a new strategy to meet industrial requirements more effectively. In this study, we conducted a comprehensive analysis of the transcriptome and metabolome of Cerrena unicolor 87613. For the first time, we discovered a negative role played by reduced glutathione (GSH) and its metabolic pathway in influencing extracellular laccase activity. Furthermore, we identified a feedback loop involving GSH, GSH synthetase gene, and GSH synthetase within this metabolic pathway. These deductions were confirmed through experimental investigations. These findings not only advanced our understanding of laccase activity regulation in its natural producer but also provide a theoretical foundation for a strategy to enhance laccase activity by reprogramming glutathione metabolism at a specific cultivation stage.