Physiological, morphological, and mannanase production studies on Aspergillus niger uam-gs1 mutants

Soledad De Nicolás-Santiago
Departamento de Biotecnología
Universidad Autónoma Metropolitana-Iztapalapa
Av. San Rafael Atlixco 186, Iztapalapa
09340 México D.F., México
Tel: 52 55 58044999
Fax: 52 55 58044712
E-mail:sol@xanum.uam.mx

Carlos Regalado-González
DIPA, PROPAC
Facultad de Química
Universidad Autónoma de Querétaro
CU. Cerro de las Campanas S/N
76010 Querétaro, Qro. México
Tel/Fax: 52 442 1921304
E-mail: carlosr@uaq.mx

Blanca García-Almendárez
DIPA, PROPAC
Facultad de Química
Universidad Autónoma de Querétaro
CU. Cerro de las Campanas S/N
76010 Querétaro, Qro. México
Tel/Fax: 52 442 1921304
E-mail: blancag@uaq.mx

Francisco J. Fernández
Departamento de Biotecnología
Universidad Autónoma Metropolitana-Iztapalapa
Av. San Rafael Atlixco 186, Iztapalapa
09340 México D.F., México
Tel: 52 55 58046453
Fax: 52 55 58044712
E-mail: fjfp@xanum.uam.mx

Alejandro Téllez-Jurado
Departamento de Biotecnología
Universidad Politécnica de Pachuca
Ex-Hacienda de Sta. Bárbara
Carretera Pachuca-Cd. Sahagún, km. 20
Zempoala, Hidalgo, Mexico
Tel/Fax: 52 743 7911800
E-mail: alito@upp.edu.mx

Sergio Huerta-Ochoa*
Departamento de Biotecnología
Universidad Autónoma Metropolitana-Iztapalapa
Av. San Rafael Atlixco 186, Iztapalapa
09340 México D.F., México
Tel: 52 55 58044999
Fax: 52 55 58044712
E-mail: sho@xanum.uam.mx

*Corresponding author

Filamentous fungi are important in industrial enzyme production, since they are able to synthesize and secrete large amounts of extra cellular proteins. These organisms grow in liquid and solid-state cultures by hyphal extension and branching. Fungal macro- and micro-morphology affect the rheology of the liquid fermentation medium, thereby having a significant impact on the mixing, mass transfer and aeration processes within the bioreactor. In addition, micro-morphology may influence metabolite productivity, which may lead to lower net specific growth rate (McIntyre et al. 2001), or to enhanced enzyme production by strains with altered morphology (McCarthy et al. 2005).

The difference of conditions between solid-state and submerged cultures can lead to altered expression of several genes, which in turn may affect various phenotypes, such as growth, development, mycotoxin and enzyme production (Iwashita, 2002). The advantages of fungal enzyme production in solid-state over liquid fermentation systems have also been pointed out (Viniegra-González et al. 2003). However, few criteria about fungal physiology and morphology in solid-state cultures have been established in the limited studies available. There are few studies relating morphology and physiology of fungi in solid-state cultures. The objective of this study was to characterize physiologically and morphologically Aspergillus niger UAM-GS1 mutants to determine the possible relationship between morphology, growth, and mannanase, cellulase and hemicellulase production of the mutant strains in solid-state fermentation.

Results and Discussion

Mutant strains from Aspergillus niger UAM-GS1 were produced by UV radiation to increase their hemicellulolytic and cellulolytic activity production. Two mutant strains (GS1-S059 and GS1-S067) showed more enzymatic activity. The mutant GS1-S067 showed a colony radial extension rate and a biomass growth rate [g biomass/(cm² h)], 1.17 times higher than that achieved by strain UAM-GS1. The high invasive capacity makes this mutant strain a promising alternative for its use in solid substrate fermentation (SSF). Using scanning electron microscopy, the morphological properties of the two mutant strains were evaluated. The diameter of the sporangium of the mutant strains GS1-S059 and GS1-S067 was significantly larger (P < 0.05) than that found for the parental strain. The hypha length and diameter of the mutant strains significantly changed (P < 0.05) compared to the parental strain. Enzymatic profile results showed that comparing to the wild strain, mannanase activity increased 3.26 times for strain GS1-S059, and 2.85 times for strain GS1-S067. In addition, cellulase production increased 3.70 times for strain GS1-S059, and 2.65 times for the mutant GS1-S067. The highest enzymatic activity increase of the mutant strains corresponded to xylanase, where strains GS1-S059 and GS1-S067 showed increases of 6.19 and 4.82 times that of the parental strain, respectively.

The relationship between physiology, morphology and enzyme production, if any, is poorly understood. Our results using A. niger mutants, obtained using UV rays, showed enhanced hemicellulolytic enzyme production and a good linear relationship between enzyme production (mannanase, cellulase and xylanase) and morphology (hyphal length and sporangium diameter).

References

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MCCARTHY, Tracey C.; LALOR, Eoin; HANNIFFY, Orla; SAVAGE, Angela V. and TUOHY, Maria G. Comparison of wild-type and UV-mutant β-glucanase-producing strains of Talaromyces emersonii with potential in brewing applications. Journal of Industrial Microbiology and Biotechnology, April 2005, vol. 32, no. 4, p. 125-134. [CrossRef]

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