Metabolic Engineering of Actinobacillus succinogenes Provides Insights into Succinic Acid Biosynthesis.

, a Gram-negative facultative anaerobe, exhibits the native capacity to convert pentose and hexose sugars to succinic acid (SA) with high yield as a tricarboxylic acid (TCA) cycle intermediate. In addition, is capnophilic, incorporating CO into SA, making this organism an ideal candidate host for conversion of lignocellulosic sugars and CO to an emerging commodity bioproduct sourced from renewable feedstocks. In this work, we report the development of facile metabolic engineering capabilities in , enabling examination of SA flux determinants via knockout of the primary competing pathways-namely, acetate and formate production-and overexpression of the key enzymes in the reductive branch of the TCA cycle leading to SA.

Metabolic engineering of Zymomonas mobilis for 2,3-butanediol production from lignocellulosic biomass sugars.

Background: To develop pathways for advanced biofuel production, and to understand the impact of host metabolism and environmental conditions on heterologous pathway engineering for economic advanced biofuels production from biomass, we seek to redirect the carbon flow of the model ethanologen Zymomonas mobilis to produce desirable hydrocarbon intermediate 2,3-butanediol (2,3-BDO). 2,3-BDO is a bulk chemical building block, and can be upgraded in high yields to gasoline, diesel, and jet fuel.

Results: 2,3-BDO biosynthesis pathways from various bacterial species were examined, which include three genes encoding acetolactate synthase, acetolactate decarboxylase, and butanediol dehydrogenase.

Succinic acid production from lignocellulosic hydrolysate by Basfia succiniciproducens.

The production of chemicals alongside fuels will be essential to enhance the feasibility of lignocellulosic biorefineries. Succinic acid (SA), a naturally occurring C4-diacid, is a primary intermediate of the tricarboxylic acid cycle and a promising building block chemical that has received significant industrial attention. Basfia succiniciproducens is a relatively unexplored SA-producing bacterium with advantageous features such as broad substrate utilization, genetic tractability, and facultative anaerobic metabolism.

Succinic acid production on xylose-enriched biorefinery streams by Actinobacillus succinogenes in batch fermentation.

Background: Co-production of chemicals from lignocellulosic biomass alongside fuels holds promise for improving the economic outlook of integrated biorefineries. In current biochemical conversion processes that use thermochemical pretreatment and enzymatic hydrolysis, fractionation of hemicellulose-derived and cellulose-derived sugar streams is possible using hydrothermal or dilute acid pretreatment (DAP), which then offers a route to parallel trains for fuel and chemical production from xylose- and glucose-enriched streams. Succinic acid (SA) is a co-product of particular interest in biorefineries because it could potentially displace petroleum-derived chemicals and polymer precursors for myriad applications.

Continuous succinic acid production by Actinobacillus succinogenes on xylose-enriched hydrolysate.

Background: Bio-manufacturing of high-value chemicals in parallel to renewable biofuels has the potential to dramatically improve the overall economic landscape of integrated lignocellulosic biorefineries. However, this will require the generation of carbohydrate streams from lignocellulose in a form suitable for efficient microbial conversion and downstream processing appropriate to the desired end use, making overall process development, along with selection of appropriate target molecules, crucial to the integrated biorefinery. Succinic acid (SA), a high-value target molecule, can be biologically produced from sugars and has the potential to serve as a platform chemical for various chemical and polymer applications.

Improving a recombinant Zymomonas mobilis strain 8b through continuous adaptation on dilute acid pretreated corn stover hydrolysate.

Background: Complete conversion of the major sugars of biomass including both the C5 and C6 sugars is critical for biofuel production processes. Several inhibitory compounds like acetate, hydroxymethylfurfural (HMF), and furfural are produced from the biomass pretreatment process leading to 'hydrolysate toxicity,' a major problem for microorganisms to achieve complete sugar utilization. Therefore, development of more robust microorganisms to utilize the sugars released from biomass under toxic environment is critical.

Improving xylose utilization by recombinant Zymomonas mobilis strain 8b through adaptation using 2-deoxyglucose.

Background: Numerous attempts have been made to improve xylose utilization in Z. mobilis including adaptive approaches. However, no one has yet found a way to overcome the reduced xylose utilization observed in fermentations carried out in the presence of glucose as well as the inhibitory compounds found within pretreated and saccharified biomass.

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

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.

Assessing the protein concentration in commercial enzyme preparations.

Although a poor indicator of how a cellulase preparation will perform on biomass, the filter paper unit (FPU) still finds wide use in the literature as an apparent measure of performance efficacy. In actuality, the assessment of commercial enzyme preparation performance in terms of biomass conversion or solubilization of insoluble polysaccharides is largely dependent on the substrate composition, which cannot be easily standardized. Commercial cellulase preparations are evaluated based upon their performance or specific activity.

Comparative performance of precommercial cellulases hydrolyzing pretreated corn stover.

Background: Cellulases and related hydrolytic enzymes represent a key cost factor for biochemical conversion of cellulosic biomass feedstocks to sugars for biofuels and chemicals production. The US Department of Energy (DOE) is cost sharing projects to decrease the cost of enzymes for biomass saccharification. The performance of benchmark cellulase preparations produced by Danisco, DSM, Novozymes and Verenium to convert pretreated corn stover (PCS) cellulose to glucose was evaluated under common experimental conditions and is reported here in a non-attributed manner.

Review of cancer registration and cancer data in Iran, a historical prospect.

Cancer data reporting in Iran dates back to 1960, when the first report of cancer frequency data was prepared and published by the late Prof. Abdollah Habibi, an Iranian pathologist working at the Cancer Institute of Iran.The next data came from two registries, one in the Caspian littoral and the other in Fars province.

Economic impact of total solids loading on enzymatic hydrolysis of dilute acid pretreated corn stover.

In process integration studies of the biomass-to-ethanol conversion process, it is necessary to understand how cellulose conversion yields vary as a function of solids and enzyme loading and other key operating variables. The impact of solids loading on enzymatic cellulose hydrolysis of dilute acid pretreated corn stover slurry was determined using an experimental response surface design methodology. From the experimental work, an empirical correlation was obtained that expresses monomeric glucose yield from enzymatic cellulose hydrolysis as a function of solids loading, enzyme loading, and temperature.

Impact of recycling stillage on conversion of dilute sulfuric acid pretreated corn stover to ethanol.

Both the current corn starch to ethanol industry and the emerging lignocellulosic biofuels industry view recycling of spent fermentation broth or stillage as a method to reduce fresh water use. The objective of this study was to understand the impact of recycling stillage on conversion of corn stover to ethanol. Sugars in a dilute-acid pretreated corn stover hydrolysate were fermented to ethanol by the glucose-xylose fermenting bacteria Zymomonas mobilis 8b.

Specific chromosomal abnormalities in patients with acute nonlymphocytic leukemia from the Islamic Republic of Iran.

Cytogenetic analysis performed at diagnosis is considered to be the most valuable prognostic factor in acute non-lymphocytic leukemia (ANLL), a very heterogeneous disease. Little data exist in Iran regarding the cytogenetic characteristics of ANLL . Therefore, cytogenetic investigations were performed for 58 patients with various subtypes of ANLL with unstimulated short term culture and high resolution cell synchronization techniques.

Performance of a newly developed integrant of Zymomonas mobilis for ethanol production on corn stover hydrolysate.

Efficient conversion of lignocellulosic biomass requires biocatalysts able to tolerate inhibitors produced by many pretreatment processes. Recombinant Zymomonas mobilis 8b, a recently developed integrant of Zymomonas mobilis 31821(pZB5), tolerated acetic acid up to 16 g l(-1) and achieved 82%-87% (w/w) ethanol yields from pure glucose/xylose solutions at pH 6 and temperatures of 30 degrees C and 37 degrees C. An ethanol yield of 85% (w/w) was achieved on glucose/xylose from hydrolysate produced by dilute sulfuric acid pretreatment of corn stover after an overliming' process was used to improve hydrolysate fermentability.

Cofermentation of glucose, xylose, and arabinose by genomic DNA-integrated xylose/arabinose fermenting strain of Zymomonas mobilis AX101.

Cofermentation of glucose, xylose, and arabinose is critical for complete bioconversion of lignocellulosic biomass, such as agricultural residues and herbaceous energy crops, to ethanol. We have previously developed a plasmid-bearing strain of Zymomonas mobilis (206C[pZB301]) capable of cofermenting glucose, xylose, and arabinose to ethanol. To enhance its genetic stability, several genomic DNA-integrated strains of Z.