Synthesis of gold nanoparticles using bacterial cellulase and its role in saccharification and bioethanol production from aquatic weeds

Abstract

In this investigation, gold nanoparticles (AuNPs) were synthesized using cellulase (partially purified from Glutamicibacter arilaitensis strain ALA4) as reducing agent. The biosynthesis of AuNPs was confirmed by observing the appearance of purple colour solution with surface plasmon resonance absorption peak (λmax) at 574 nm. The SEM analysis showed the synthesis of gold nanocrystals with an average size of 5–7 nm. Cellulase was partially purified from strain ALA4 using standard protocols, and further immobilized on AuNPs for assessing its role in the saccharification of alkali (4% w/v NaOH) pre-treated aquatic weeds (Alternanthera philoxeroides and Brachiaria mutica) biomass. The pre-treated biomass of A. philoxeroides exhibited maximum total reducing sugar (TRS) yield of 18.95 ± 0.18 mg/g at 72 h. The pre-treated biomass exhibited increased saccharification degree of 38.25 ± 0.8, 49.05 ± 0.7, 67.05 ± 0.7, 85.27 ± 0.8, and 67.99 ± 0.8% from 12 to 96 h. Likewise, the pre-treated biomass of B. mutica exhibited maximum TRS yield of 20.98 ± 0.17 mg/g at 72 h. The pre-treated biomass exhibited increased saccharification degree of 44.46 ± 0.7, 55.53 ± 0.8, 73.26 ± 0.7, 94.41 ± 0.8, and 73.3 ± 0.7% from 12 to 96 h. Bioethanol production from pre-treated aquatic weeds were estimated by simultaneous saccharification and fermentation process using yeast cells immobilized on sodium alginate. Ethanol content was estimated using Gas Chromatography. The yeast cells immobilized in calcium alginate beads showed ethanol production of 45.09 and 50.1% from NaOH pre-treated A. philoxeroides and B. mutica biomass, respectively. Findings of this study suggested pronounced role of bacterial cellulase-assisted-synthesized AuNPs in biofuel industries for the successful production of bioethanol from distinct aquatic weeds biomass in a cost-effective manner in future.