Enhancement of exopolysaccharide production from Ganoderma lucidum using a novel submerged volatile co-culture system

Adding-value to Ganoderma lingzhi by producing enzymes and antioxidant compounds under submerged fermentation using different culture media

Ganoderma lingzhi is widely reported for its medicinal properties, presenting several bioactive substances with potential pharmaceutical and industrial application. This study aimed to evaluate the production of mycelial biomass, extracellular enzymes and antioxidant compounds by G. lingzhi under submerged fermentation. G. lingzhi was cultured in Polysaccharide (POL) and Melin-Norkrans (MNM) media for 7 days. The cellulases, xylanases, pectinases, laccases, and proteases activities were quantified in the culture broth, while the antioxidant potential was evaluated for the mycelial biomass. G. lingzhi showed higher biomass production in MNM. However, it exhibited similar microstructural characteristics in both culture media. In the POL there was greater activity of CMCase (0.229 U/mL), xylanase (0.780 U/mL), pectinase (0.447 U/mL) and proteases (16.13 U/mL). FPase did not differ (0.01 U/mL), and laccase was detected only in MNM (0.122 U/mL). The biomass water extract from MNM showed high levels of phenolic compounds (951.97 mg AGE/100 g). DPPH• inhibition (90.55%) and reducing power (0.456) were higher in MNM medium, while ABTS•+ inhibition (99.95%) and chelating ability (54.86%) were higher in POL. Thus, the MNM medium was more favorable to the production of mycelial biomass and phenolic compounds, while the POL medium favored the synthesis and excretion of hydrolytic enzymes.

Bio-stimulating effect of endophytic Aspergillus flavus AUMC 16068 and its respective ex-polysaccharides in lead stress tolerance of Triticum aestivum plant

Heavy metal accumulation is one of the major agronomic challenges that has seriously threatened food safety. As a result, metal-induced phytotoxicity concerns require quick and urgent action to retain and maintain the physiological activities of microorganisms, the nitrogen pool of soils, and the continuous yields of wheat in a constantly worsening environment. The current study was conducted to evaluate the plant growth-promoting endophytic Aspergillus flavus AUMC 16,068 and its EPS for improvement of plant growth, phytoremediation capacity, and physiological consequences on wheat plants (Triticum aestivum) under lead stress. After 60 days of planting, the heading stage of wheat plants, data on growth metrics, physiological properties, minerals content, and lead content in wheat root, shoot, and grains were recorded. Results evoked that lead pollution reduced wheat plants' physiological traits as well as growth at all lead stress concentrations; however, inoculation with lead tolerant endophytic A. flavus AUMC 16,068 and its respective EPS alleviated the detrimental impact of lead on the plants and promoted the growth and physiological characteristics of wheat in lead-contaminated conditions and also lowering oxidative stress through decreasing (CAT, POD, and MDA), in contrast to plants growing in the un-inoculated lead polluted dealings. In conclusion, endophytic A. flavus AUMC 16,068 spores and its EPS are regarded as eco-friendly, safe, and powerful inducers of wheat plants versus contamination with heavy metals, with a view of protecting plant, soil, and human health.

The key technologies of Ganoderma lucidum liquid spawn preparation and scale expansion

Ganoderma lucidum possesses a variety of valuable pharmacological activities, and it has long been used to prevent and treat various human diseases. Up to now, far too little attention has been paid to the liquid spawn of G. lucidum, and the development of the G. lucidum industry is constrained by them. This work aimed to study the key technologies and scale-up preparation of G. lucidum liquid spawn, to achieve large-scale preparation of liquid spawn and solve the problem of unstable quality of G. lucidum. The plate culture, primary shake flask culture, shake flask preparation, and fermentor preparation of G. lucidum liquid spawn were explored in the process of liquid fermentation. The results showed that plate broth volume significantly affected mycelial growth rate. Biomass in the primary shake flask culture is significantly influenced by the picking position of plate mycelium. An artificial neural network coupled with a genetic algorithm was used for carbon and nitrogen sources concentration optimization to increase biomass and substrate utilization. The optimized parameter combination is as follows: glucose, 14.5 g L^-1; yeast extract powder, 8.5 g L^-1. Under this condition, the biomass (9.82 g L^-1) and biomass on reducing sugar (0.79 g g^-1) increased by 18.03% and 27.41% compared to the control, respectively. The metabolic activity of liquid spawn prepared by different fermentation scales was diverse, and the liquid spawn prepared by the fermentor has better activity. Conceivably, the liquid spawn process can more conducive be applied to large-scale industrial production.

Microbial production of valuable chemicals by modular co-culture strategy

Nowadays, microbial synthesis has become a common way for producing valuable chemicals. Traditionally, microbial production of valuable chemicals is accomplished by a single strain. For the purpose of increasing the production titer and yield of a recombinant strain, complicated pathways and regulation layers should be fine-tuned, which also brings a heavy metabolic burden to the host. In addition, utilization of various complex and mixed substrates further interferes with the normal growth of the host strain and increases the complexity of strain engineering. As a result, modular co-culture technology, which aims to divide a target complex pathway into separate modules located at different single strains, poses an alternative solution for microbial production. Recently, modular co-culture strategy has been employed for the synthesis of different natural products. Therefore, in this review, various chemicals produced with application of co-cultivation technology are summarized, including co-culture with same species or different species, and regulation of population composition between the co-culture members. In addition, development prospects and challenges of this promising field are also addressed, and possible solution for these issues were also provided.

Contrasting regulation of live Bacillus cereus No.1 and its volatiles on Shiraia perylenequinone production

BACKGROUND

Fungal perylenequinones (PQs) are a class of photoactivated polyketide mycotoxins produced by plant-associated fungi. Hypocrellins, the effective anticancer photodynamic therapy (PDT) agents are main bioactive PQs isolated from a bambusicolous Shiraia fruiting bodies. We found previously that bacterial communities inhabiting fungal fruiting bodies are diverse, but with unknown functions. Bacillus is the most dominant genus inside Shiraia fruiting body. To understand the regulation role of the dominant Bacillus isolates on host fungus, we continued our work on co-culture of the dominant bacterium B. cereus No.1 with host fungus Shiraia sp. S9 to elucidate bacterial regulation on fungal hypocrellin production.

RESULTS

Results from "donut" plate tests indicated that the bacterial culture could promote significantly fungal PQ production including hypocrellin A (HA), HC and elsinochrome A-C through bacterial volatiles. After analysis by gas chromatograph/mass spectrometer and confirmation with commercial pure compounds, the volatiles produced by the bacterium were characterized. The eliciting roles of bacterial volatile organic compounds (VOCs) on HA production via transcriptional regulation of host Shiraia fungus were confirmed. In the established submerged bacterial volatile co-culture, bacterial volatiles could not only promote HA production in the mycelium culture, but also facilitate the release of HA into the medium. The total production of HA was reached to 225.9 mg/L, about 1.87 times that of the fungal mono-culture. In contrast, the live bacterium suppressed markedly fungal PQ production in both confrontation plates and mycelium cultures by direct contact. The live bacterium not only down-regulated the transcript levels of HA biosynthetic genes, but also degraded extracellular HA quickly to its reductive product.

CONCLUSION

Our results indicated that bacterial volatile release could be a long-distance signal to elicit fungal PQ production. Biodegradation and inhibition by direct contact on fungal PQs were induced by the dominate Bacillus to protect themselves in the fruiting bodies. This is the first report on the regulation of Bacillus volatiles on fungal PQ production. These findings could be helpful for both understanding the intimate fungal-bacterial interactions in a fruiting body and establishing novel cultures for the enhanced production of bioactive PQs.

Anthocyanin extract from Lycium ruthenicum enhanced production of biomass and polysaccharides during submerged fermentation of Agaricus bitorquis (Quél.) Sacc. Chaidam

Agaricus bitorquis (Quél.) Sacc. Chaidam (ABSC) is a wild edible fungus uniquely found in the Tibet Plateau. ABSC is rich in polysaccharides that are considered biologically active. This study aimed to determine the feasibility of enhancing exopolysaccharide (EPS) production by ABSC in shake flask culture by supplementing the fermentation medium with anthocyanin extract. Different concentrations of Lycium ruthenicum Murr. (LRM) anthocyanin crude extract were tested on ABSC fermentation. The activity of phosphoglucose isomerase (PGI), phosphoglucose mutase (PGM), and phosphomannose isomerase (PMI), enzymes presumably involved in EPS synthesis by ABSC, was determined. ABSC transcriptomic profile in response to the presence of anthocyanins during fermentation was also investigated. LRM anthocyanin crude extract (0.06 mg/mL) was most effective in increasing EPS content and mycelial biomass (by 208.10% and 105.30%, respectively, P < 0.01). The activity of PGI, PGM, and PMI was increased in a medium where LRM anthocyanin extract and its main components (proanthocyanidins and petunia anthocyanin) were added. RNA-Seq analysis showed that 349 genes of ABSC were differentially expressed during fermentation in the medium containing anthocyanin extract of LRM; 93 genes were up-regulated and 256 genes down-regulated. From gene ontology enrichment analysis, differentially expressed genes were mostly assigned to carbohydrate metabolism and signal transduction categories. Collectively, LRM anthocyanins extract positively affected EPS production and mycelial biomass during ABSC fermentation. Our study provides a novel strategy for improving EPS production and mycelial growth during ABSC liquid submerged fermentation.

Mutation, Chemoprofiling, Dereplication, and Isolation of Natural Products from Penicillium oxalicum

Diethyl sulfate (DES)-based chemical mutagenesis was applied on different fungal strains with the aim of diversifying the secondary metabolites. The mutant strain (VRE-MT1) of Penicillium oxalicum was subjected to dereplication (LCMS-based) and isolation of natural products, resulting in obtaining 10 molecules of bioactive potential. Metabolites, viz. tuckolide, methylpenicinoline, 2-acetyl-3,5-dihydroxy-4,6-dimethylbenzeneacetic acid, penicillixanthone A, brefeldin A 7-ketone, and antibiotic FD 549, were observed for the first time from P. oxalicum. The results of antimicrobial activity reveal that the compounds N-[2-(4-hydroxyphenyl)ethenyl]formamide, methylpenicinoline, and penipanoid A have potent antibacterial activity against Bacillus subtilis (ATCC 6633) with minimum inhibitory concentration (MIC) values of 16, 64, and 16 μM, respectively, and the compounds N-[2-(4-hydroxyphenyl)ethenyl]formamide, methylpenicinoline, and penipanoid A were found active against Escherichia coli (ATCC 25922), with MIC values of 16, 64, and 16 μM, respectively. Also, the metabolites N-[2-(4-hydroxyphenyl)ethenyl]formamide and tuckolide showed effective antioxidant activity in 2,2-diphenyl-1-picrylhydrazyl and 2,2'-azino-bis(3-ethylbenzothiazoline)-6-sulfonic acid scavenging assays. The mutant VRE-MT1 was found to have 8.34 times higher quantity of N-[2-(4-hydroxyphenyl)ethenyl]formamide as compared to the mother strain. The DES-based mutagenesis strategy has been found to be a potent tool to diversify the secondary metabolites in fungi.

GapB Is Involved in Biofilm Formation Dependent on LrgAB but Not the SinI/R System in Bacillus cereus 0-9

Bacillus cereus 0-9, a Gram-positive endospore-forming bacterium isolated from healthy wheat roots, has biological control capacity against several soil-borne plant diseases of wheat such as sharp eyespot and take-all. The bacterium can produce various biofilms that differ in their architecture and formation mechanisms, possibly for adapting to different environments. The gapB gene, encoding a glyceraldehyde-3-phosphate dehydrogenase (GAPDH), plays a key role in B. cereus 0-9 biofilm formation. We studied the function of GapB and the mechanism of its involvement in regulating B. cereus 0-9 biofilm formation. GapB has GAPDH activities for both NAD⁺- and NADP⁺-dependent dehydrogenases and is a key enzyme in gluconeogenesis. Biofilm yield of the ΔgapB strain decreased by 78.5% compared with that of wild-type B. cereus 0-9 in lysogeny broth supplemented with some mineral salts (LBS), and the ΔgapB::gapB mutants were recovered with gapB gene supplementation. Interestingly, supplementing the LBS medium with 0.1-0.5% glycerol restored the biofilm formation capacity of the ΔgapB mutants. Therefore, GapB regulates biofilm formation relative to its function in gluconeogenesis. To illustrate how GapB is involved in regulating biofilm formation through gluconeogenesis, we carried out further research. The results indicate that the GapB regulated the B. cereus 0-9 biofilm formation independently of the exopolysaccharides and regulatory proteins in the typical SinI/R system, likely owing to the release of extracellular DNA in the matrix. Transcriptome analysis showed that the gapB deletion caused changes in the expression levels of only 18 genes, among which, lrgAB was the most significantly increased by 6.17-fold. We confirmed this hypothesis by counting the dead and living cells in the biofilms and found the number of living cells in the biofilm formed by the ΔgapB strain was nearly 7.5 times than that of wild-type B. cereus 0-9. Therefore, we concluded that the GapB is involved in the extracellular DNA release and biofilm formation by regulating the expression or activities of LrgAB. These results provide a new insight into the regulatory mechanism of bacterial biofilm formation and a new foundation for further studying the stress resistance of B. cereus.