High-throughput screening carbon and nitrogen sources to promote growth and sporulation in Rhizopus arrhizus

Rhizopus arrhizus is a saprotrophic, sometimes clinically- and industrially-relevant mold (Mucorales) and distributed worldwide, suggesting it can assimilate a broad spectrum of substrates. Here, 69 strains of R. arrhizus were investigated by using the Biolog FF MicroPlate for the profiles of utilizing 95 carbon and nitrogen substrates. The study showed that most R. arrhizus strains were similar in average well color development (AWCD) and substrate richness (SR). Nevertheless, 13 strains were unique in principal component analyses, heatmap, AWCD, and SR analyses, which may imply a niche differentiation within R. arrhizus. The species R. arrhizus was able to utilize all the 95 carbon and nitrogen substrates, consistent with the hypothesis of a great metabolic diversity. It possessed a substrate preference of alcohols, and seven substrates were most frequently utilized, with N-acetyl-D-galactosamine and L-phenylalanine ranking at the top of the list. Eight substrates, especially L-arabinose and xylitol, were capable of promoting sporulation and being applied for rejuvenating degenerated strains. By phenotyping R. arrhizus strains in carbon and nitrogen assimilation capacity, this study revealed the extent of intra-specific variability and laid a foundation for estimating optimum substrates that may be useful for industrial applications.

Potato peel waste fermentation by Rhizopus oryzae to produce lactic acid and ethanol

Potato peel waste (PPW), a zero-value by-product generated from potato processing, is a promising fermentation substrate due to its large quantity of starch, nonstarch polysaccharides, lignin, protein, and lipid. Rhizopus oryzae is a filamentous fungus that is mainly known as a lactic acid producer and can ferment various agro-wastes. This study aimed to use R. oryzae for the fermentation of PPW. A series of batch fermentations were conducted to investigate the effects of different PPW loading rates (2%-8%) and particle sizes (0-4 mm). Under an initial PPW loading rate of 8% and particle size of 1-2 mm, the maximum ethanol (18.83 g/L) and lactic acid (3.14 g/L) concentrations, the highest ethanol (9.41 g/L·day) and lactic acid (1.89 g/L·day) average production rates were obtained. Under these conditions, the yield of ethanol and lactic acid was 0.235 g/gPPW and 0.039 g/gPPW, respectively. R. oryzae was shown to utilize PPW as a substrate to produce value-added bioproducts such as ethanol (major product) and lactic acid.

Rhizopus oryzae - Ancient microbial resource with importance in modern food industry

Filamentous fungi are microorganisms widely known for their diverse biochemical features. Fungi can efficiently invade a wide variety of substrates under operational conditions producing numerous bioproducts of interest, such as enzymes, organic acids, aromatic compounds and colorants. An additional interesting characteristic of some fungi is their safety classification for different uses, which guarantees that the bioproducts obtained from them do not contain any toxic component deleterious to humans. Rhizopus oryzae is among this group of fungi and is classified as a GRAS filamentous fungus, commonly used for production of some oriental traditional foods. It is mainly recognized as a good producer of lactic acid; however, its potential for other biotechnological processes is under study. This review analyzes and discusses the current scientific and technical contributions which may maximize the potential of R. oryzae as a producer of different compounds of industrial interest.