Regulation of secondary metabolism by calmodulin signaling in filamentous fungi

Comparative Genomic Analysis Reveals Key Changes in the Genome of Acremonium chrysogenum That Occurred During Classical Strain Improvement for Production of Antibiotic Cephalosporin C

From the 1950s to the present, the main tool for obtaining fungal industrial producers of secondary metabolites remains the so-called classical strain improvement (CSI) methods associated with multi-round random mutagenesis and screening for the level of target products. As a result of the application of such techniques, the yield of target secondary metabolites in high-yielding (HY) strains was increased hundreds of times compared to the wild-type (WT) parental strains. However, the events that occur at the molecular level during CSI programs are still unknown. In this paper, an attempt was made to identify characteristic changes at the genome level that occurred during CSI of the Acremonium chrysogenum WT strain (ATCC 11550) and led to the creation of the A. chrysogenum HY strain (RNCM F-4081D), which produces 200-300 times more cephalosporin C, the starting substance for obtaining cephalosporin antibiotics of the 1st-5th generations. We identified 3730 mutational changes, 56 of which led to significant disturbances in protein synthesis and concern: (i) enzymes of primary and secondary metabolism; (ii) transporters, including MDR; (iii) regulators, including cell cycle and chromatin remodeling; (iv) other processes. There was also a focus on mutations occurring in the biosynthetic gene clusters (BGCs) of the HY strain; polyketide synthases were found to be hot spots for mutagenesis. The obtained data open up the possibility not only for understanding the molecular basis for the increase in cephalosporin C production in A. chrysogenum HY, but also show the universal events that occur when improving mold strains for the production of secondary metabolites by classical methods.

Regulatory Role of Vacuolar Calcium Transport Proteins in Growth, Calcium Signaling, and Cellulase Production in Trichoderma reesei

Recent research has revealed the calcium signaling significance in the production of cellulases in Trichoderma reesei. While vacuoles serve as the primary calcium storage within cells, the function of vacuolar calcium transporter proteins in this process remains unclear. In this study, we conducted a functional characterization of four vacuolar calcium transport proteins in T. reesei. This was accomplished by the construction of the four mutant strains ∆trpmc1, ∆tryvc1, ∆tryvc3, and ∆tryvc4. These mutants displayed enhanced growth when subjected to arabinose, xylitol, and xylose. Furthermore, the mutants ∆trpmc1, ∆tryvc1, and ∆tryvc4 showed a reduction in growth under conditions of 100 mM MnCl2, implying their role in manganese resistance. Our enzymatic activity assays revealed a lack of the expected augmentation in cellulolytic activity that is typically seen in the parental strain following the introduction of calcium. This was mirrored in the expression patterns of the cellulase genes. The vacuolar calcium transport genes were also found to play a role in the expression of genes involved with the biosynthesis of secondary metabolites. In summary, our research highlights the crucial role of the vacuolar calcium transporters and, therefore, of the calcium signaling in orchestrating cellulase and hemicellulase expression, sugar utilization, and stress resistance in T. reesei.

Stress-driven metabolites of desert soil fungi

Microorganisms produce secondary metabolites to survive under stressful conditions. The effect of drought and heat stress on fungi isolated from Arabian desert soil during the hot (ca 40°C) and cool (ca 10°C) seasons was studied using the genome mining approach. The presence of three stress-related genes (calmodulin, polyketide synthase and beta tubulin) was analyzed molecularly using specific primers. The presence of the genes in desert fungi was compared to their antimicrobial (ten bacterial or fungal pathogens) and anticancer (liver, cervical and breast) properties and the production of thermostable enzymes (phytase and xylanase). The genes appeared to be present in the fungal sequence obtained during the summer, while none of the genes were present during winter. Appreciable differences were observed in enzyme activities, with summer activities high and winter low. The antagonistic activities of A. niger were relatively stable and varying, while those of P. chrysogenum were consistently higher in summer than in winter. The presence of the three genes seemed to correlate with the highly antagonistic activities of P. chrysogenum, while A. niger had relatively active winter isolates without any of the genes. The hot season in deserts yields fungal isolates with biological activities useful in biotechnological solutions.

Vacuolal and Peroxisomal Calcium Ion Transporters in Yeasts and Fungi: Key Role in the Translocation of Intermediates in the Biosynthesis of Fungal Metabolites

Highlights

The intracellular calcium content plays a key role in the expression of genes involved in the biosynthesis and secretion of fungal metabolites.

The cytosolic calcium concentration in fungi is maintained by influx through the cell membrane and by release from store organelles.

Some MSF transporters, e.g., PenV of Penicillium chrysogenum and CefP of Acremonium chrysogenum belong to the TRP calcium ion channels.

A few of the numerous calcium ion transporters existing in organelles of different filamentous fungi have been characterized at the functional and subcellular localization levels.

The cytosolic calcium signal seems to be transduced by the calcitonin/calcineurin cascade controlling the expression of many fungal genes.

Abstract

The intracellular calcium content in fungal cells is influenced by a large number of environmental and nutritional factors. Sharp changes in the cytosolic calcium level act as signals that are decoded by the cell gene expression machinery, resulting in several physiological responses, including differentiation and secondary metabolites biosynthesis. Expression of the three penicillin biosynthetic genes is regulated by calcium ions, but there is still little information on the role of this ion in the translocation of penicillin intermediates between different subcellular compartments. Using advanced information on the transport of calcium in organelles in yeast as a model, this article reviews the recent progress on the transport of calcium in vacuoles and peroxisomes and its relation to the translocation of biosynthetic intermediates in filamentous fungi. The Penicillium chrysogenum PenV vacuole transporter and the Acremonium chrysogenum CefP peroxisomal transporter belong to the transient receptor potential (TRP) class CSC of calcium ion channels. The PenV transporter plays an important role in providing precursors for the biosynthesis of the tripeptide δ-(-α-aminoadipyl-L-cysteinyl-D-valine), the first intermediate of penicillin biosynthesis in P. chrysogenum. Similarly, CefP exerts a key function in the conversion of isopenicillin N to penicillin N in peroxisomes of A. chrysogenum. These TRP transporters are different from other TRP ion channels of Giberella zeae that belong to the Yvc1 class of yeast TRPs. Recent advances in filamentous fungi indicate that the cytosolic calcium concentration signal is connected to the calcitonin/calcineurin signal transduction cascade that controls the expression of genes involved in the subcellular translocation of intermediates during fungal metabolite biosynthesis. These advances open new possibilities to enhance the expression of important biosynthetic genes in fungi.