Genome shuffling of Aspergillus glaucus HGZ-2 for enhanced cellulase production

Comparative Analysis of Structural Variations Due to Genome Shuffling of Bacillus Subtilis VS15 for Improved Cellulase Production

Cellulose is one of the most abundant and renewable biomass products used for the production of bioethanol. Cellulose can be efficiently hydrolyzed by Bacillus subtilis VS15, a strain isolate obtained from decomposing logs. A genome shuffling approach was implemented to improve the cellulase activity of Bacillus subtilis VS15. Mutant strains were created using ethyl methyl sulfonate (EMS), N-Methyl-N′ nitro-N-nitrosoguanidine (NTG), and ultraviolet light (UV) followed by recursive protoplast fusion. After two rounds of shuffling, the mutants Gb2, Gc8, and Gd7 were produced that had an increase in cellulase activity of 128%, 148%, and 167%, respectively, in comparison to the wild type VS15. The genetic diversity of the shuffled strain Gd7 and wild type VS15 was compared at whole genome level. Genomic-level comparisons identified a set of eight genes, consisting of cellulase and regulatory genes, of interest for further analyses. Various genes were identified with insertions and deletions that may be involved in improved celluase production in Gd7. Strain Gd7 maintained the capability of hydrolyzing wheatbran to glucose and converting glucose to ethanol by fermentation with Saccharomyces cerevisiae of the wild type VS17. This ability was further confirmed by the acidified potassium dichromate (K₂Cr₂O₇) method.

Genome shuffling and high-throughput screening of Brevibacterium flavum MDV1 for enhanced L-valine production

L-valine is an essential branched-amino acid that is widely used in multiple areas such as pharmaceuticals and special dietary products and its use is increasing. As the world market for L-valine grows rapidly, there is an increasing interest to develop an efficient L-valine-producing strain. In this study, a simple, sensitive, efficient, and consistent screening procedure termed 96 well plate-PC-HPLC (96-PH) was developed for the rapid identification of high-yield L-valine strains to replace the traditional L-valine assay. L-valine production by Brevibacterium flavum MDV1 was increased by genome shuffling. The starting strains were obtained using ultraviolet (UV) irradiation and binary ethylenimine treatment followed by preparation of protoplasts, UV irradiation inactivation, multi-cell fusion, and fusion of the inactivated protoplasts to produce positive colonies. After two rounds of genome shuffling and the 96-PH method, six L-valine high-yielding mutants were selected. One genetically stable mutant (MDVR2-21) showed an L-valine yield of 30.1 g/L during shake flask fermentation, 6.8-fold higher than that of MDV1. Under fed-batch conditions in a 30 L automated fermentor, MDVR2-21 accumulated 70.1 g/L of L-valine (0.598 mol L-valine per mole of glucose; 38.9% glucose conversion rate). During large-scale fermentation using a 120 m3 fermentor, this strain produced > 66.8 g/L L-valine (36.5% glucose conversion rate), reflecting a very productive and stable industrial enrichment fermentation effect. Genome shuffling is an efficient technique to improve production of L-valine by B. flavum MDV1. Screening using 96-PH is very economical, rapid, efficient, and well-suited for high-throughput screening.

An efficient genetic manipulation protocol for Ustilago esculenta

Ustilago esculenta grows within the flowering stem of the aquatic grass Zizania latifolia, resembling a fungal endophyte. The fungus colonizes Z. latifolia and induces swelling which results in the formation of galls near the base of the plant. Due to their unique flavor and textures these galls are considered as a delicacy in southern China. Efficient genetic manipulation is required to determine the relationship between U. esculenta and Z. latifolia. In this study, we report a protoplast-based transformation system for this unique fungal species. We have explored various factors (enzyme digesting conditions, osmotic pressure stabilizers, vectors and selection agents) that might impact protoplast yield and high frequencies of transformation. A haploid strain (UeT55) of U. esculenta was found to produce higher yields of protoplasts when treating with 15 mg mL(-1) lywallzyme in a sucrose-containing solution at 30°C for 3 h. The transformation frequencies were higher when fungal strain was transformed with a linear plasmid harboring hygromycin or carboxin resistance gene and regenerated on a sucrose-containing medium. A UeICL gene (coding isocitrate lyase) was disrupted and an EGFP (coding enhanced green fluorescent protein) gene was overexpressed successfully in the UeT55 strain using the developed conditions. The genetic manipulation system reported in this study will open up new opportunities for forward and reverse genetics in U. esculenta.

Destructuring plant biomass: focus on fungal and extremophilic cell wall hydrolases

The use of plant biomass as feedstock for biomaterial and biofuel production is relevant in the current bio-based economy scenario of valorizing renewable resources. Fungi, which degrade complex and recalcitrant plant polymers, secrete different enzymes that hydrolyze plant cell wall polysaccharides. The present review discusses the current research trends on fungal, as well as extremophilic cell wall hydrolases that can withstand extreme physico-chemical conditions required in efficient industrial processes. Secretomes of fungi from the phyla Ascomycota, Basidiomycota, Zygomycota and Neocallimastigomycota are presented along with metabolic cues (nutrient sensing, coordination of carbon and nitrogen metabolism) affecting their composition. We conclude the review by suggesting further research avenues focused on the one hand on a comprehensive analysis of the physiology and epigenetics underlying cell wall degrading enzyme production in fungi and on the other hand on the analysis of proteins with unknown function and metagenomics of extremophilic consortia. The current advances in consolidated bioprocessing, altered secretory pathways and creation of designer plants are also examined. Furthermore, recent developments in enhancing the activity, stability and reusability of enzymes based on synergistic, proximity and entropic effects, fusion enzymes, structure-guided recombination between homologous enzymes and magnetic enzymes are considered with a view to improving saccharification.