Differential temperature effect on the production of enhanced gamma linolenic acid in Mucor rouxii CFR-G15

Evaluation of Different Standard Amino Acids to Enhance the Biomass, Lipid, Fatty Acid, and γ-Linolenic Acid Production in Rhizomucor pusillus and Mucor circinelloides

In this study, 18 standard amino acids were tested as a single nitrogen source on biomass, total lipid, total fatty acid (TFA) production, and yield of γ-linolenic acid (GLA) in Rhizomucor pusillus AUMC 11616.A and Mucor circinelloides AUMC 6696.A isolated from unusual habitats. Grown for 4 days at 28°C, shaking at 150 rpm, the maximum fungal biomass for AUMC 6696.A was 14.6 ± 0.2 g/L with arginine and 13.68 ± 0.1 g/L with asparagine, when these amino acids were used as single nitrogen sources, while AUMC 11616.A maximum biomass was 10.73 ± 0.8 g/L with glycine and 9.44 ± 0.6 g/L with valine. These were significantly higher than the ammonium nitrate control (p < 0.05). The highest levels of TFA were achieved with glycine for AUMC 11616.A, 26.2 ± 0.8% w/w of cell dry weight, and glutamic acid for AUMC 6696.A, 23.1 ± 1.3%. The highest GLA yield was seen with proline for AUMC 11616.A, 13.4 ± 0.6% w/w of TFA, and tryptophan for AUMC 6696.A, 12.8 ± 0.3%, which were 38% and 25% higher than the ammonium tartrate control. The effects of environmental factors such as temperature, pH, fermentation time, and agitation speed on biomass, total lipids, TFA, and GLA concentration of the target strains have also been investigated. Our results demonstrated that nitrogen assimilation through amino acid metabolism, as well as the use of glucose as a carbon source and abiotic factors, are integral to increasing the oleaginicity of tested strains. Few studies have addressed the role of amino acids in fermentation media, and this study sheds light on R. pusillus and M. circinelloides as promising candidates for the potential applications of amino acids as nitrogen sources in the production of lipids.

The Potential of Single-Cell Oils Derived From Filamentous Fungi as Alternative Feedstock Sources for Biodiesel Production

Microbial lipids, also known as single-cell oils (SCOs), are highly attractive feedstocks for biodiesel production due to their fast production rates, minimal labor requirements, independence from seasonal and climatic changes, and ease of scale-up for industrial processing. Among the SCO producers, the less explored filamentous fungi (molds) exhibit desirable features such as a repertoire of hydrolyzing enzymes and a unique pellet morphology that facilitates downstream harvesting. Although several oleaginous filamentous fungi have been identified and explored for SCO production, high production costs and technical difficulties still make the process less attractive compared to conventional lipid sources for biodiesel production. This review aims to highlight the ability of filamentous fungi to hydrolyze various organic wastes for SCO production and explore current strategies to enhance the efficiency and cost-effectiveness of the SCO production and recovery process. The review also highlights the mechanisms and components governing lipogenic pathways, which can inform the rational designs of processing conditions and metabolic engineering efforts for increasing the quality and accumulation of lipids in filamentous fungi. Furthermore, we describe other process integration strategies such as the co-production with hydrogen using advanced fermentation processes as a step toward a biorefinery process. These innovative approaches allow for integrating upstream and downstream processing units, thus resulting in an efficient and cost-effective method of simultaneous SCO production and utilization for biodiesel production.

Robust and cost-saving static solid cultivation method for lipid production using the chlamydospores of Phanerochaete chrysosporium

BACKGROUND

During current submerged fermentation for microbial lipid production, the large-scale reactor operations inevitably consume substantial amounts of water and electricity for aeration, stirring, and temperature control and result in the operational costs almost exceeding the biodiesel value produced. Thus, developing a novel low-cost cultivation strategy is urgently needed by microbial lipid industry.

RESULTS

The filamentous fungus Phanerochaete chrysosporium can synthesize and accumulate lipids via static solid cultivation. The conversion efficiency of substrates to lipids reaches 0.277 g/g substrate after optimization of the following cultivation factors: humidity, solid medium thickness, temperature, and rotary speed. The lipids obtained by static solid cultivation differ in component and relative content from those achieved by submerged cultivation. Laser scanning confocal microscopy reveals that numerous chlamydospores filled with lipids appear during static solid cultivation, and the fungal morphological change explains why static solid cultivation is superior in lipid yield compared with submerged fermentation. The genes coding the enzymes related to fatty acid elongation and degradation are differently expressed during static solid cultivation, which presents an answer to the appearance of abundant saturated long-chain fatty acids (93.6% in total fatty acids) in chlamydospores. In addition, engineering viability and cost-benefit analysis show that the conversion of wheat bran and glucose to lipid by the fungus is efficient. More importantly, the solid cultivation incurs only a small reactor operational cost because neither cooling water nor electrical equipment, including aerator, stirrer, and the temperature control system, is used.

CONCLUSIONS

This study developed a robust and cost-saving solid fermentation method without an aerator, stirrer, and temperature control system to produce microbial lipids using the chlamydospores of P. chrysosporium. Compared with conventional submerged fermentation, the solid cultivation strategy is promising because it diminishes most of the reactor operational costs, including water and power expenses.