Enhancement of protoplast preparation and regeneration of Hirsutella sinensis based on process optimization

Establishment of an Agrobacterium tumefaciens-Mediated Transformation System for Hirsutella sinensis

Ophiocordyceps sinensis (Berk.) is a complex is formed by Hepialidae larvae and Hirsutella sinensis. Infestation by H. sinensis, interaction with host larvae, and fruiting body development are three crucial processes affecting the formation of O. sinensis. However, research on the molecular mechanism of O. sinensis formation has been hindered by the lack of effective genetic transformation protocols. Therefore, Agrobacterium tumefaciens-mediated transformation (ATMT) was adopted to genetically transform two H. sinensis strains and optimize the transformation conditions. The results revealed that the most suitable Agrobacterium strain for H. sinensis transformation was AGL1, and that the surfactant Triton X-100 could also induce ATMT, although less effectively than acetosyringone (AS). In addition, the endogenous promoters of H. sinensis genes had a stronger ability to drive the expression of the target gene than did the exogenous promoter. The optimal transformation conditions were as follows: AS and hygromycin B concentrations of 100 μM and 50 μg/mL, respectively; A. tumefaciens OD600 of 0.4; cocultivation at 18 °C for 24 h; and H. sinensis used within three passages. The results lay a foundation for the functional study of key regulatory genes involved in the formation of O. sinensis.

Exploration of the pneumocandin biosynthetic gene cluster based on efficient CRISPR/Cas9 gene editing strategy in Glarea lozoyensis

Pneumocandin B0 (PB0) is a lipopeptide produced by the fungus Glarea lozoyensis. The existing challenges with the low-yield and the extended-fermentation cycle emphasize necessity for strain improvement. In this study, we optimized conditions to obtain high-quality protoplasts and screened effective selection markers, leading to the construction of three CRISPR/Cas9 gene editing systems. Utilizing a constitutive Cas9 expression recipient strain, combined with dual sgRNAs targeting, we achieved highly efficient editing of target genes. We successfully knocked out 10 genes within the pneumocandin putative biosynthetic gene cluster and analyzed their roles in PB0 production. Our findings reveal that 4 of 10 genes are directly involved in PB0 production. Specially, the deletion of gltrt or gl10050 resulted in reduced PB0 production, while the absence of glhyp or glhtyC led to the complete loss of PB0 biosynthesis. Notably, the deletion of glhyp caused the silencing of nearly all cluster genes, whereas overexpression of glhyp led to a 2.38-fold increase in PB0 production. Therefore, this study provides the first comprehensive exploration of the functions of 10 genes within the pneumocandin putative biosynthetic gene cluster. Our findings provide valuable technical strategies for constructing bioengineering strains with purposefully enhanced PB0 production.

Development of lead (Pb) tolerant strain by protoplast technology and their remediation

The lead is poisonous metal and because of its chemical nature it acts as an environmental contaminant through the water or soil and it becomes toxic to humans. The toxicity of Pb occurs as a change in the conformation of nucleic acid and protein, inhibition of enzyme activity, disruption of membrane function and oxidative phosphorylation. For protoplast preparation, the removal of the cell wall and protoplast formation obtained by specific lytic enzyme. In cytoplasmic membrane, the envelope of bacteria consists of overlying cell wall. From hypertonic environment, the complete cell wall removal occurs due to which it maintains the osmotic integrity of the cell and produces the protoplast. In current work, protoplasts were produced by specific lytic enzyme (lysozyme and macerozyme), chemo fused (with the help of Polyethylene Glycol) and regenerated from strains Staphylococcus sp. and Bacillus sp. The fused protoplast was spherical in shape observed under microscopy. Colonies were screened on specific medium supplemented with Pb (Concentration at the rate of 1.5mM). One resistant colony (MICBT-1) was selected and further examined and applied for the transformation of Pb in the broth medium. The strain removed 98% of Pb at 1mM concentration. Next, sucrose containing medium was best which gives maximum protoplast regeneration. From various organisms, fusion technique has been used to combine the genes to create the strains having desired properties. This is a significant technique for engineering of bacterial strains for advantageous applied properties. Further MICBT-1 applied in artificially contaminated soil and removed maximally in exchangeable fraction (remains up to 0.05 mM). An efficient bioremediating agent for lead transformation from soil and water is expected to ease the ever-increasing problem. Further, it is needful to obtain new strain with the help of protoplast technology which can reduce the pollutant. This lead tolerant strain can be applied for bioremediation purposes in the Pb contaminated soil and water environment.

CRISPR/Cas9 RNP-assisted validation of palmarumycin biosynthetic gene cluster in Lophiotrema sp. F6932

Lophiotrema is a genus of ascomycetous fungi within the family Lophiotremataceae. Members of this genus have been isolated as endophytes from a wide range of host plants and also from plant debris within terrestrial and marine habitats, where they are thought to function as saprobes. Lophiotrema sp. F6932 was isolated from white mangrove (Avicennia officinalis) in Pulau Ubin Island, Singapore. Crude extracts from the fungus exhibited strong antibacterial activity, and bioassay-guided isolation and structure elucidation of bioactive constituents led to the isolation of palmarumycin C8 and a new analog palmarumycin CP30. Whole-genome sequencing analysis resulted in the identification of a putative type 1 iterative PKS (iPKS) predicated to be involved in the biosynthesis of palmarumycins. To verify the involvement of palmarumycin (PAL) gene cluster in the biosynthesis of these compounds, we employed ribonucleoprotein (RNP)-mediated CRISPR-Cas9 to induce targeted deletion of the ketosynthase (KS) domain in PAL. Double-strand breaks (DSBs) upstream and downstream of the KS domain was followed by homology-directed repair (HDR) with a hygromycin resistance cassette flanked by a 50 bp of homology on both sides of the DSBs. The resultant deletion mutants displayed completely different phenotypes compared to the wild-type strain, as they had different colony morphology and were no longer able to produce palmarumycins or melanin. This study, therefore, confirms the involvement of PAL in the biosynthesis of palmarumycins, and paves the way for implementing a similar approach in the characterization of other gene clusters of interest in this largely understudied fungal strain.

Optimization of Protoplast Preparation and Establishment of Genetic Transformation System of an Arctic-Derived Fungus Eutypella sp

Arctic-derived fungus Eutypella sp. D-1 has attracted wide attention due to its huge ability to synthesize secondary metabolites. However, current studies only focus on stimulating its production of new secondary metabolites by OSMAC strategies, and the relationship between secondary metabolites and biosynthetic gene clusters (BGCs) has not been explored. In this study, the preparation and regeneration conditions of Eutypella sp. D-1 protoplasts were explored to lay a foundation for the study of genetic transformation of this fungus. Orthogonal experiment showed that the optimal preparation conditions were 0.75 M NaCl, 20 g/L of lysing enzyme, and 20 g/L of driselase, 28°C for 6 h. The maximum yield of Eutypella sp. D-1 protoplasts could reach 6.15 × 10⁶ cells·ml⁻¹, and the concentration of osmotic stabilizer NaCl was the most important factor for Eutypella sp. D-1 protoplasts. The results of FDA staining showed that the prepared protoplasts had good activity. Besides, the best protoplasts regeneration medium was YEPS, whose maximum regeneration rate is 36%. The mediums with nitrogen sources, such as SR and RM, also had good effects on the Eutypella sp. D-1 protoplast regeneration, indicating that nitrogen sources played an important role on the Eutypella sp. D-1 protoplast regeneration. Subsequent transformation experiments showed that hygromycin resistance genes (hrg) could be successfully transferred into the genome of Eutypella sp. D-1, indicating that the prepared protoplasts could meet the needs of subsequent gene manipulation and research. This study lays a foundation for the genetic transformation of Eutypella sp. D-1.

Improvement of cordycepin production by an isolated Paecilomyces hepiali mutant from combinatorial mutation breeding and medium screening

Cordycepin is a major bioactive compound found in Cordyceps sinensis that exhibits a broad spectrum of biological activities. Here a Paecilomyces hepiali OR-1 strain was initially isolated from plateau soil for the bioproduction of cordycepin. Subsequently, strain modification including ⁶⁰Co γ-ray and ultraviolet irradiation were employed to increase the cordycepin titer, resulted in a high-yield mutant strain P. hepiali ZJB18001 with the cordycepin content of 0.61 mg/g_DCW, showing a 2.3-fold to that from the wild strain (0.26 mg/g_DCW). Furthermore, medium screening based on Box-Behnken design and the response surface methodology facilitated the enhancement of cordycepin yield to the value of 0.96 mg/g_DCW at 25 °C for 5 days in submerged cultivation with an optimized medium composition. The high cordycepin yield, rapid growth rate and stable genetic characteristics of P. hepiali ZJB18001 are beneficial in terms of costs and time for the industrialization of cordycepin production.

Genetic Manipulation of the Brassicaceae Smut Fungus Thecaphora thlaspeos

Investigation of plant–microbe interactions greatly benefit from genetically tractable partners to address, molecularly, the virulence and defense mechanisms. The smut fungus Ustilago maydis is a model pathogen in that sense: efficient homologous recombination and a small genome allow targeted modification. On the host side, maize is limiting with regard to rapid genetic alterations. By contrast, the model plant Arabidopsis thaliana is an excellent model with a vast amount of information and techniques as well as genetic resources. Here, we present a transformation protocol for the Brassicaceae smut fungus Thecaphora thlaspeos. Using the well-established methodology of protoplast transformation, we generated the first reporter strains expressing fluorescent proteins to follow mating. As a proof-of-principle for homologous recombination, we deleted the pheromone receptor pra1. As expected, this mutant cannot mate. Further analysis will contribute to our understanding of the role of mating for infection biology in this novel model fungus. From now on, the genetic manipulation of T. thlaspeos, which is able to colonize the model plant A. thaliana, provides us with a pathosystem in which both partners are genetically amenable to study smut infection biology.