Isolation and Screening of Halotolerant Fungi for Cellulase Activity from Mangrove Sediments of the Arabian Gulf

  • Celia García-Baños López

Student thesis: Master's Thesis

Abstract

Cellulases are enzymes that deconstruct cellulose to glucose. Their use is a prerequisite step for ethanol production from cellulose and there is interest world-wide in activity optimization and/or identification of highly efficient variants. The biofuel industry is also becoming interested in replacing freshwater with seawater for biomass processing. This necessitates cellulases that are effective in high salt solutions. This study explores the potential for identifying novel cellulases sourced from halotolerant fungi that are suitable for biomass processing in seawater rather than freshwater. A total of 10 fungi were isolated to purity from mangrove soil sediments using Gulf Sea water salt concentrations (4.8% w/v). They were then identified by sequencing of Internal Transcribed Spacers of ribosomal RNA genes. Two of the 10 isolates, identified as Acremonium implicatum and Alternaria sp., were examined further in the lab for their growth response and for cellulase activity present in ‘spent' filtrates when salt (NaCl) concentrations reaching up to 10% (w/v) is supplemented into their growth medium. The growth of both isolates was negatively impacted by salt concentrations above 4.8% (w/v), but total cellulase activity of crude protein fractions were not affected when measured via the filter paper assay. Interestingly though, the concentration of salt appears to differentially impact ß –glucosidase activity in the two isolates. Specifically, in Alternaria sp., the highest ß –glucosidase activity (27 pmol glucose released / µg protein x min-1) in crude filtrates was detected when it was grown in 0% salt (w/v) vs. for A. implicatum the highest activity (12 pmol glucose released / µg protein x min-1) was detected when it was grown in 2.4% (w/v) salt medium. Finally, crude extracellular proteins were fractionated on an anionic exchange column using Fast Protein Liquid Chromatography and compared with commercial Trichoderma reesei purified enzymes. Our preliminary investigation suggests promising ß-glucosidase activity results. The end goal is to develop a cellulase cocktail formulation that is suitable for deconstruction of industrially-relevant substrates in high salt solutions.
Date of Award2014
Original languageAmerican English
SupervisorLina Yousef (Supervisor)

Keywords

  • Mangrove forests; Mangrove conservation; Mangrove ecology; Mangrove swamp ecology.

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