Designer synthetic media for studying microbial-catalyzed biofuel production

Abstract

BackgroundThe fermentation inhibition of yeast or bacteria by lignocellulose-derived degradation products, during hexose/pentose co-fermentation, is a major bottleneck for cost-effective lignocellulosic biorefineries. To engineer microbial strains for improved performance, it is critical to understand the mechanisms of inhibition that affect fermentative organisms in the presence of major components of a lignocellulosic hydrolysate. The development of a synthetic lignocellulosic hydrolysate (SH) media with a composition similar to the actual biomass hydrolysate will be an important advancement to facilitate these studies. In this work, we characterized the nutrients and plant-derived decomposition products present in AFEX™ pretreated corn stover hydrolysate (ACH). The SH was formulated based on the ACH composition and was further used to evaluate the inhibitory effects of various families of decomposition products during Saccharomyces cerevisiae 424A (LNH-ST) fermentation.ResultsThe ACH contained high levels of nitrogenous compounds, notably amides, pyrazines, and imidazoles. In contrast, a relatively low content of furans and aromatic and aliphatic acids were found in the ACH. Though most of the families of decomposition products were inhibitory to xylose fermentation, due to their abundance, the nitrogenous compounds showed the most inhibition. From these compounds, amides (products of the ammonolysis reaction) contributed the most to the reduction of the fermentation performance. However, this result is associated to a concentration effect, as the corresponding carboxylic acids (products of hydrolysis) promoted greater inhibition when present at the same molar concentration as the amides.Due to its complexity, the formulated SH did not perfectly match the fermentation profile of the actual hydrolysate, especially the growth curve. However, the SH formulation was effective for studying the inhibitory effect of various compounds on yeast fermentation.ConclusionsThe formulation of SHs is an important advancement for future multi-omics studies and for better understanding the mechanisms of fermentation inhibition in lignocellulosic hydrolysates. The SH formulated in this work was instrumental for defining the most important inhibitors in the ACH. Major AFEX decomposition products are less inhibitory to yeast fermentation than the products of dilute acid or steam explosion pretreatments; thus, ACH is readily fermentable by yeast without any detoxification.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-014-0179-6) contains supplementary material, which is available to authorized users.

Transcriptome analysis revealed the dynamic oil accumulation in Symplocos paniculata fruit

“…6). Similar results were seen in Siberian apricot ( Prunus sibirica ) [15] and tung oil tree ( Vernicia fordii ) [52]. A low expression of ACC genes at 80 and 140 DAF might be related to the remarkable accumulation of fatty acids in this development stage (oleic acid, C18:1 is one major component of S. paniculata ) (Additional file 2: Figure S2).…”

“…It is widely used for exploring functional genes [11], constructing expression and transcriptional regulatory profiles [12], discovering molecular markers such as simple sequence repeats (SSRs) and single nucleotide polymorphisms (SNPs) [13, 14], and investigating comparative and evolutionary genomics [15, 16]. This technique is efficient to generate a large amount of genetic data.…”

Flowthrough pretreatment with very dilute acid provides insights into high lignin contribution to biomass recalcitrance

“…At 140 °C for 192 min, lignin removals from flowthrough pretreatments were 63% in LHW and 67% in EDA. It is important to note that while lignin removal was only slightly enhanced in EDA compared to LHW flowthrough pretreatment, Zhang et al [45] report a larger increase in lignin removal in EDA compared to LHW flowthrough pretreatment. This outcome can be due to their use of more severe pretreatment conditions ranging between 160 and 270 °C for 0–12 min at a linear velocity of 18.94 cm/min.…”

Pre-senescence Harvest of Switchgrass Inhibits Xylose Utilization by Engineered Yeast

“…This may indicate that temperature is a key factor dictating conversion of ferulic acid and pcoumaric acid to the amide form, and the relative selectivity of ammonolysis and hydrolysis reactions (Chundawat et al, 2010). The acid form is generally more inhibitory compared to the amide form (Tang et al, 2015) and this could be one contributor toward the lower ethanol yields of the switchgrass pretreated at low severity. Additionally, the formation of ketones was only observed at the higher ammonia pretreatment severity.…”