Inhibition of growth of Zymomonas mobilis by model compounds found in lignocellulosic hydrolysates

Abstract

Background: During the pretreatment of biomass feedstocks and subsequent conditioning prior to saccharification, many toxic compounds are produced or introduced which inhibit microbial growth and in many cases, production of ethanol. An understanding of the toxic effects of compounds found in hydrolysate is critical to improving sugar utilization and ethanol yields in the fermentation process. In this study, we established a useful tool for surveying hydrolysate toxicity by measuring growth rates in the presence of toxic compounds, and examined the effects of selected model inhibitors of aldehydes, organic and inorganic acids (along with various cations), and alcohols on growth of Zymomonas mobilis 8b (a ZM4 derivative) using glucose or xylose as the carbon source. Results: Toxicity strongly correlated to hydrophobicity in Z. mobilis, which has been observed in Escherichia coli and Saccharomyces cerevisiae for aldehydes and with some exceptions, organic acids. We observed Z. mobilis 8b to be more tolerant to organic acids than previously reported, although the carbon source and growth conditions play a role in tolerance. Growth in xylose was profoundly inhibited by monocarboxylic organic acids compared to growth in glucose, whereas dicarboxylic acids demonstrated little or no effects on growth rate in either substrate. Furthermore, cations can be ranked in order of their toxicity, Ca

Mixed Carboxylic Acid Production by Megasphaera elsdenii from Glucose and Lignocellulosic Hydrolysate

“…It is worth noting that xylose is a major component of these sugars streams and the M. elsdenii strain employed here cannot utilize xylose or other pentose sugars. Regardless, it is important to demonstrate that M. elsdenii can tolerate these streams since they have been reported to be toxic for other organisms due to the presence of potential bacterial inhibitors such as acetate, furfural, and phenolic compounds [39]. Considering that xylose is not utilized by this bacterium, a batch experiment in serum bottles was performed; in a fed-batch pertractive fermentation, xylose would accumulate to high concentrations in the fermentor and may present an extra inhibitory effect in the bacterium due to increased osmotic stress.…”

Progress and perspective on lignocellulosic hydrolysate inhibitor tolerance improvement in Zymomonas mobilis

“…The major components of glucose, xylose, arabinose, acetic acid, and furans, as well as a wide variety of aliphatic acid compounds can be detected directly from hydrolysate samples by highperformance liquid chromatography (HPLC) or gas chromatography (GC) using different columns and detectors (Franden et al 2013;Gu et al 2014). Minor components, especially for phenolic compounds, have been extracted from hydrolysate using organic solvents, concentrated by evaporation, and analyzed by gas chromatographymass spectrometer (GC-MS), liquid chromatographymass spectrometer (LC-MS), and/or inductively coupled plasma mass spectrometer (ICP-MS) (Gu et al 2014;Wang et al 2014).…”

“…Although Z. mobilis demonstrates advantages in ethanol fermentation, the inhibitors derived from biomass deconstruction and hydrolysis still have detrimental effects on Z. mobilis, especially when high biomass solid loading is used during pretreatment and enzymatic hydrolysis steps to generate high concentration of sugars besides the potential additive or synergistic inhibitions of various inhibitors in the hydrolysate (Franden et al 2013). In this review, we reviewed the progress of strain improvement in Z. mobilis to enhance its lignocellulosic hydrolysate inhibitor tolerance capability for economic lignocellulosic biochemical production.…”

Development of corn silk as a biocarrier for <i>Zymomonas mobilis</i> biofilms in ethanol production from rice straw

“…Vanillin, syringaldehyde and 4-HB are formed by the degradation of lignin. The presence of these compounds has been shown to synergistically reduce the growth rate of microorganisms by disturbing the cell membrane function, inhibiting essential enzymes, negatively interacting with DNA and RNA, and specifically interacting with the Entner Doudoroff pathway mRNA (Banerjee et al, 1981;Franden et al, 2013;He et al, 2014). Despite these adverse conditions, we found that rice straw hydrolysate can be used by Z. mobilis (strains TISTR405, 550 and 551) in biofilms on polystyrene surfaces (3 days old) to produce higher ethanol yields (Y P/S ) than planktonic or suspended cultures (Table 2).…”

“…Bioethanol production from lignocellulosic material has been considered as an alternative source of bioenergy due terials and result in a reduction in ethanol production through the growth, enzymatic and metabolic effects (Franden et al, 2013;Ranatunga et al, 1997). Therefore, the detoxification process needs to be carried out either by physical and biological pretreatment, prior to the fermentation process which leads to increased production costs and process complexity (Klinke et al, 2004).…”