Establishing a microbial co-culture for production of cellulase using banana (musa paradisiaca) pseudostem

Abstract

In nature, saccharification is done by a variety of microorganisms, secreting a variety of cellulase in addition to other proteins. Co-culturing enables the production of more efficient enzyme preparations that would mimic the natural decomposition of lignocelluloses. During the decay of banana (Musa paradisiaca) pseudostem, a potential feedstock for second-generation biofuels, there may be a number of microorganisms producing cellulolytic enzymes, and other factors, which in combination might decompose the lignocelluloses more efficiently. The aim of the study was to establish a microbial co-culture for the production of highly active cellulase preparations. Banana pseudostems (BPS) and microbial samples from decaying banana pseudostems were collected in the Mopani District Allesbeste Nursery, Limpopo Province, South Africa. Fungi and bacteria were isolated using CMC agar plates. The best cellulase producing fungi and bacteria were tested for cellulase activity in monocultures and in various combinations (fungi-fungi, fungi-bacteria, bacteria-bacteria, fungi-live bacterial cells and fungi-dead bacterial cells) in submerged fermentation, using Avicel™ as a carbon source. Solid-state fermentation was also performed using banana pseudostem as a carbon source. Zymography was done in studying the variety of cellulase in the secretions from co-cultures/ mixed cultures. Identification of the bacterial and fungal isolates from decomposing banana pseudostems was also done using matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) or DNA sequencing. A mixed culture of fungi in combination with dead bacterial cells was the best combination to produce higher levels of endoglucosidase and β-glucosidase activities in both submerged fermentation and solid-state fermentation. During SmF, endoglucosidase was (0.229 after 144 h) and β-glucosidase (4.519 after 96 h) activities and SSF, endoglucosidase (12.793 after 48 h) and β-glucosidase (37.45 after 144 h). Endoglucosidase zymography showed that monocultures and co-cultures produced four active bands for endoglucanase, except for the monoculture Trichoderma longibrachiatum 1B that produced a faint or unclear band. The current study demonstrated that three fungal strains namely, T longibrachiatum 1B, Aspergillus fumigatus 5A, and Aspergillus flavus 2A and one bacterial strain Enterobacter asburiae 1 are capable of producing a variety of endoglucanases. It seems that a combination of fungi with dead cells could significantly improve endoglucosidase and v β-glucosidase activities. The use of A. fumigatus in mixed cultures is highly recommended in order to produce high levels of β-glucosidases, no matter the combination used.