Ethanol production by a Paenibacillus species isolated from an Icelandic hot spring: Production yields from complex biomass

Abstract

Ethanol production using Paenibacillus strain J2 was studied on carbohydrates and lignocellulosic biomass hydrolysates including grass (Phleum pratense) and barley straw (Hordeum vulgare). The strain has a broad substrate spectrum; fermentation of glucose yielded ethanol (major product), acetate, butyrate (minor), hydrogen, and carbon dioxide. At glucose concentrations below 30 mM fermentation was not inhibited. Higher substrate loadings resulted in decreased glucose utilization and a shift of end products towards butyrate. The maximum yields of ethanol were 1.45 mol ethanol mol glucose-1. The end products from lignocellulosic (4.5 g L-1 dw) biomass hydrolysates pretreated with 0.5% HCl or NaOH (control was unpretreated) prior to cellulase treatment were investigated. Ethanol production from cellulose hydrolysates without chemical pre-treatment yielded 5.5 mM ethanol g-1 with lower yields from paper and lignocellulosic biomasses (1.2-1.7 mM g-1). Ethanol production was enhanced by dilute acid or base pre-treatment combined with enzymatic treatment with the highest yields from grass (3.2 mM ethanol g-1).