Metabolic engineering of Caldicellulosiruptor bescii for hydrogen production.

Hydrogen is an alternative fuel for transportation vehicles because it is clean, sustainable, and highly flammable. However, the production of hydrogen from lignocellulosic biomass by microorganisms presents challenges. This microbial process involves multiple complex steps, including thermal, chemical, and mechanical treatment of biomass to remove hemicellulose and lignin, as well as enzymatic hydrolysis to solubilize the plant cell walls. These steps not only incur costs but also result in the production of toxic hydrolysates, which inhibit microbial growth. A hyper-thermophilic bacterium of Caldicellulosiruptor bescii can produce hydrogen by decomposing and fermenting plant biomass without the need for conventional pretreatment. It is considered as a consolidated bioprocessing (CBP) microorganism. This review summarizes the basic scientific knowledge and hydrogen-producing capacity of C. bescii. Its genetic system and metabolic engineering strategies to improve hydrogen production are also discussed. KEY POINTS: • Hydrogen is an alternative and eco-friendly fuel. • Caldicellulosiruptor bescii produces hydrogen with a high yield in nature. • Metabolic engineering can make C. bescii to improve hydrogen production.

Hydrogen Production from Barley Straw and Miscanthus by the Hyperthermophilic Bacterium, Cadicellulosirupter bescii.

This work aimed to evaluate the feasibility of biohydrogen production from Barley Straw and Miscanthus. The primary obstacle in plant biomass decomposition is the recalcitrance of the biomass itself. Plant cell walls consist of cellulose, hemicellulose, and lignin, which make the plant robust to decomposition. However, the hyperthermophilic bacterium, Caldicellulosiruptor bescii, can efficiently utilize lignocellulosic feedstocks (Barley Straw and Miscanthus) for energy production, and C. bescii can now be metabolically engineered or isolated to produce more hydrogen and other biochemicals. In the present study, two strains, C. bescii JWCB001 (wild-type) and JWCB018 (ΔpyrFA Δldh ΔcbeI), were tested for their ability to increase hydrogen production from Barley Straw and Miscanthus. The JWCB018 resulted in a redirection of carbon and electron (carried by NADH) flow from lactate production to acetate and hydrogen production. JWCB018 produced ~54% and 63% more acetate and hydrogen from Barley Straw, respectively than its wild-type counterpart, JWCB001. Also, 25% more hydrogen from Miscanthus was obtained by the JWCB018 strain with 33% more acetate relative to JWCB001. It was supported that the engineered C. bescii, such as the JWCB018, can be a parental strain to get more hydrogen and other biochemicals from various biomass.

Sustainable Production of Shinorine from Lignocellulosic Biomass by Metabolically Engineered Saccharomyces cerevisiae.

Mycosporine-like amino acids (MAAs) have been used in cosmetics and pharmaceuticals. The purpose of this work was to develop yeast strains for sustainable and economical production of MAAs, especially shinorine. First, genes involved in MAA biosynthetic pathway from Actinosynnema mirum were introduced into Saccharomyces cerevisiae for heterologous shinorine production. Second, combinatorial expression of wild and mutant xylose reductase was adopted in the engineered S. cerevisiae to facilitate xylose utilization in the pentose phosphate pathway. Finally, the accumulation of sedoheptulose 7-phosphate (S7P) was attempted by deleting transaldolase-encoding TAL1 in the pentose phosphate pathway to increase carbon flux toward shinorine production. In fed-batch fermentation, the engineered strain (DXdT-M) produced 751 mg/L shinorine in 71 h. Ultimately, 54 mg/L MAAs was produced by DXdT-M from rice straw hydrolysate. The results suggest that shinorine production by S. cerevisiae might be a promising process for sustainable production and industrial applications.

Metabolism perturbation Causedby the overexpression of carbon monoxide dehydrogenase/Acetyl-CoA synthase gene complex accelerated gas to acetate conversion rate ofEubacterium limosumKIST612.

Microbial conversion of carbon monoxide (CO) to acetate is a promising upcycling strategy for carbon sequestration. Herein, we demonstrate that CO conversion and acetate production rates of Eubacterium limosum KIST612 strain can be improved by in silico prediction and in vivo assessment. The mimicked CO metabolic model of KIST612 predicted that overexpressing the CO dehydrogenase (CODH) increases CO conversion and acetate production rates. To validate the prediction, we constructed mutant strains overexpressing CODH gene cluster and measured their CO conversion and acetate production rates. A mutant strain (ELM031) co-overexpressing CODH, coenzyme CooC2 and ACS showed a 3.1 × increased specific CO oxidation rate as well as 1.4 × increased specific acetate production rate, compared to the wild type strain. The transcriptional and translational data with redox balance analysis showed that ELM031 has enhanced reducing potential from up-regulation of ferredoxin and related metabolism directly linked to energy conservation.

Coexpression of a ß-d-Xylosidase from Thermotoga maritima and a Family 10 Xylanase from Acidothermus cellulolyticus Significantly Improves the Xylan Degradation Activity of the Caldicellulosiruptor bescii Exoproteome.

Caldicellulosiruptor species are hyperthermophilic, Gram-positive anaerobes and the most thermophilic cellulolytic bacteria so far described. They have been engineered to convert switchgrass to ethanol without pretreatment and represent a promising platform for the production of fuels, chemicals, and materials from plant biomass. Xylooligomers, such as xylobiose and xylotriose, that result from the breakdown of plant biomass more strongly inhibit cellulase activity than do glucose or cellobiose. High concentrations of xylobiose and xylotriose are present in C. bescii fermentations after 90 h of incubation, and removal or breakdown of these types of xylooligomers is crucial to achieving high conversion of plant biomass to product. In previous studies, the addition of exogenous ß-d-xylosidase substantially improved the performance of glucanases and xylanases in vitro. ß-d-Xylosidases are, in fact, essential enzymes in commercial preparations for efficient deconstruction of plant biomass. In addition, the combination of xylanase and ß-d-xylosidase is known to exhibit synergistic action on xylan degradation. In spite of its ability to grow efficiently on xylan substrates, no extracellular ß-d-xylosidase was identified in the C. bescii genome. Here, we report that the coexpression of a thermal stable ß-d-xylosidase from Thermotoga maritima and a xylanase from Acidothermus cellulolyticus in a C. bescii strain containing the A. cellulolyticus E1 endoglucanase significantly increased the activity of the exoproteome as well as growth on xylan substrates. The combination of these enzymes also resulted in increased growth on crystalline cellulose in the presence of exogenous xylan. IMPORTANCECaldicellulosiruptor species are bacteria that grow at extremely high temperature, more than 75°C, and are the most thermophilic bacteria so far described that are capable of growth on plant biomass. This native ability allows the use of unpretreated biomass as a growth substrate, eliminating the prohibitive cost of preprocessing/pretreatment of the biomass. They only grow under strictly anaerobic conditions, and the combination of high temperature and the lack of oxygen reduces the cost of fermentation and contamination by other microbes. They have been genetically engineered to convert switchgrass to ethanol without pretreatment and represent a promising platform for the production of fuels, chemicals, and materials from plant biomass. In this study, we introduced genes from other cellulolytic bacteria and identified a combination of enzymes that improves growth on plant biomass. An important feature of this study is that it measures growth, validating predictions made from adding enzyme mixtures to biomass.

Gene-Centric Metagenome Analysis Reveals Gene Clusters for Carbon Monoxide Conversion and Validates Isolation of a Clostridial Acetogen for C2 Chemical Production.

Syngas fermentation is largely dependent on acetogens that occur in various anaerobic environmental samples including soil, sediment, and feces. Here the authors report the metagenomic isolation of acetogens for C2 chemical production from syngas. Screening acetogens for C2 chemical production typically involves detecting the presence of the Wood-Ljungdahl Pathway for carbon monoxide conversion. The authors collect samples from river-bed sediments potentially having conditions suitable for carbon monoxide-converting anaerobes, and enrich the samples under carbon monoxide selection pressure. Changes in the microbial community during the experimental procedure are investigated using both amplicon and shotgun metagenome sequencing. Combined next-generation sequencing techniques enabl in situ tracking of the major acetogenic bacterial group and lead to the discovery of a 16 kb of gene cluster for WLP. The authors isolat an acetogenic clostridial strain from the enrichment culture (strain H21-9). The functional activity of H21-9 is confirmed by its high level of production of C2 chemicals from carbon monoxide (77.4 mM acetate and 2.5 mM of ethanol). This approach of incorporating experimental enrichment with metagenomic analysis can facilitate the discovery of novel strains from environmental habitats by tracking target strains during the screening process, combined with validation of their functional activity.

The Effects of Curcuma longa L., Purple Sweet Potato, and Mixtures of the Two on Immunomodulation in C57BL/6J Mice Infected with LP-BM5 Murine Leukemia Retrovirus.

The immune response is stimulated to protect the body from external antigens and is controlled by several types of immune cells. In the present study, the immunomodulatory effects of Curcuma longa L., purple sweet potato, and mixtures of the two (CPM) were investigated in C57BL/6 mice infected with LP-BM5 murine leukemia virus (MuLV). Mice were divided into seven groups as follows: normal control, infected control (LP-BM5 MuLV infection), positive control (LP-BM5 MuLV infection+dietary supplement of red ginseng 300 mg/kg body weight), the original powder of C. longa L. (C; LP-BM5 MuLV infection+dietary supplement of C 189 mg/kg body weight), the original powder of purple sweet potato (P; LP-BM5 MuLV infection+dietary supplement of P 1811 mg/kg body weight), CPM Low (CPL; LP-BM5 MuLV infection+CPM 2 g/kg body weight), and CPM High (CPH; LP-BM5 MuLV infection+CPM 5 g/kg body weight). Dietary supplementation lasted for 12 weeks. Dietary supplementation of CPM inhibited LP-BM5 MuLV-induced lymphadenopathy and splenomegaly and inhibited reduction of messenger RNA (mRNA) expression of major histocompatibility complex (MHC) I and II. Moreover, CPM reduced the decrease in T- and B cell proliferation, reduced the population of CD4(+)/CD8(+) T cells, and remedied the unbalanced production of T helper-1 (Th1)/T helper-2 (Th2) cytokines in LP-BM5 MuLV-infected mice. In addition, CPM inhibited reduction of phagocytosis in peritoneal macrophages and decreased serum levels of immunoglobulin A (IgA), immunoglobulin E (IgE), and immunoglobulin G (IgG). These results suggest that CPM had a positive effect on immunomodulation in C57BL/6 mice induced by LP-BM5 leukemia retrovirus infection.

Acetate-assisted increase of butyrate production by Eubacterium limosum KIST612 during carbon monoxide fermentation.

The acetate-assisted cultivation of Eubacterium limosum KIST612 was found to provide a way for enhancing cell mass, the carbon monoxide (CO) consumption rate, and butyrate production using CO as an electron and energy source. Cell growth (146%), µmax (121%), and CO consumption rates (151%) increased significantly upon the addition of 30mM acetate to microbial cultures. The main product of CO fermentation by E. limosum KIST612 shifted from acetate to butyrate in the presence of acetate, and 5.72mM butyrate was produced at the end of the reaction. The resting cell experimental conditions indicated acetate uptake and an increase in the butyrate concentration. Three routes to acetate assimilation and energy conservation were suggested based on given experimental results and previously genome sequencing data. Acetate assimilation via propionate CoA-transferase (PCT) was expected to produce 1.5mol ATP/mol butyrate, and was thus anticipated to be the most preferred route.

Deletion of a gene cluster for [Ni-Fe] hydrogenase maturation in the anaerobic hyperthermophilic bacterium Caldicellulosiruptor bescii identifies its role in hydrogen metabolism.

The anaerobic, hyperthermophlic, cellulolytic bacterium Caldicellulosiruptor bescii grows optimally at ∼80 °C and effectively degrades plant biomass without conventional pretreatment. It utilizes a variety of carbohydrate carbon sources, including both C5 and C6 sugars, released from plant biomass and produces lactate, acetate, CO2, and H2 as primary fermentation products. The C. bescii genome encodes two hydrogenases, a bifurcating [Fe-Fe] hydrogenase and a [Ni-Fe] hydrogenase. The [Ni-Fe] hydrogenase is the most widely distributed in nature and is predicted to catalyze hydrogen production and to pump protons across the cellular membrane creating proton motive force. Hydrogenases are the key enzymes in hydrogen metabolism and their crystal structure reveals complexity in the organization of their prosthetic groups suggesting extensive maturation of the primary protein. Here, we report the deletion of a cluster of genes, hypABFCDE, required for maturation of the [Ni-Fe] hydrogenase. These proteins are specific for the hydrogenases they modify and are required for hydrogenase activity. The deletion strain grew more slowly than the wild type or the parent strain and produced slightly less hydrogen overall, but more hydrogen per mole of cellobiose. Acetate yield per mole of cellobiose was increased ∼67 % and ethanol yield per mole of cellobiose was decreased ∼39 %. These data suggest that the primary role of the [Ni-Fe] hydrogenase is to generate a proton gradient in the membrane driving ATP synthesis and is not the primary enzyme for hydrogen catalysis. In its absence, ATP is generated from increased acetate production resulting in more hydrogen produced per mole of cellobiose.

Cellulosic ethanol production via consolidated bioprocessing at 75 °C by engineered Caldicellulosiruptor bescii.

BACKGROUND: The C. bescii genome does not encode an acetaldehyde/alcohol dehydrogenase or an acetaldehyde dehydrogenase and no ethanol production is detected in this strain. The recent introduction of an NADH-dependent AdhE from C. thermocellum (Fig. 1a) in an ldh mutant of this strain resulted in production of ethanol from un-pretreated switchgrass, but the thermolability of the C. thermocellum AdhE at the optimum growth temperature of C. bescii (78 °C) meant that ethanol was not produced above 65 °C.Fig. 1Proposed scheme for the pyruvate to ethanol pathway in C. thermocellum and T. pseudethanolicus 39E. a The C. thermocellum ethanol pathway. The red colored AdhE (Cthe_0423) is already expressed and tested in C. bescii [26]. b The T. pseudethanolicus 39E ethanol pathway. The green colored AdhE (Teth39_0206) and blue colored AdhB (Teth39_0218) are expressed and tested in C. bescii in this study. RESULTS: The adhB and adhE genes from Thermoanaerobacter pseudethanolicus 39E, an anaerobic thermophile that produces ethanol as a major fermentation product at 70 °C, were cloned and expressed in an ldh deletion mutant of C. bescii. The engineered strains produced ethanol at 75 °C, near the ethanol boiling point. The AdhB expressing strain produced ethanol (1.4 mM on Avicel, 0.4 mM on switchgrass) as well as acetate (13.0 mM on Avicel, 15.7 mM on switchgrass). The AdhE expressing strain produced more ethanol (2.3 mM on Avicel, 1.6 mM on switchgrass) and reduced levels of acetate (12.3 mM on Avicel, 15.1 mM on switchgrass). These engineered strains produce cellulosic ethanol at the highest temperature of any microorganism to date. In addition, the addition of 40 mM MOPS to the growth medium increased the maximal growth yield of C. bescii by approximately twofold. CONCLUSIONS: The utilization of thermostable enzymes will be critical to achieving high temperature CBP in bacteria such as C. bescii. The ability to produce ethanol at 75 °C, near its boiling point, raises the possibility that process optimization could allow in situ product removal of this end product to mitigate ethanol toxicity.

Expression of the Acidothermus cellulolyticus E1 endoglucanase in Caldicellulosiruptor bescii enhances its ability to deconstruct crystalline cellulose.

BACKGROUND: The Caldicellulosiruptor bescii genome encodes a potent set of carbohydrate-active enzymes (CAZymes), found primarily as multi-domain enzymes that exhibit high cellulolytic and hemicellulolytic activity on and allow utilization of a broad range of substrates, including plant biomass without conventional pretreatment. CelA, the most abundant cellulase in the C. bescii secretome, uniquely combines a GH9 endoglucanase and a GH48 exoglucanase in one protein. The most effective commercial enzyme cocktails used in vitro to pretreat biomass are derived from fungal cellulases (cellobiohydrolases, endoglucanases and a ß-d-glucosidases) that act synergistically to release sugars for microbial conversion. The C. bescii genome contains six GH5 domains in five different open reading frames. Four exist in multi-domain proteins and two as single catalytic domains. E1 is a GH5 endoglucanase reported to have high specific activity and simple architecture and is active at the growth temperature of C. bescii. E1 is an endo-1,4-ß-glucanase linked to a family 2 carbohydrate-binding module shown to bind primarily to cellulosic substrates. We tested if the addition of this protein to the C. bescii secretome would improve its cellulolytic activity. RESULTS: In vitro analysis of E1 and CelA shows synergistic interaction. The E1 gene from Acidothermus cellulolyticus was cloned and expressed in C. bescii under the transcriptional control of the C. bescii S-layer promoter, and secretion was directed by the addition of the C. bescii CelA signal peptide sequence. The vector was integrated into the C. bescii chromosome at a site previously showing no detectable detrimental consequence. Increased activity of the secretome of the strain containing E1 was observed on both carboxymethylcellulose (CMC) and Avicel. Activity against CMC increased on average 10.8 % at 65 °C and 12.6 % at 75 °C. Activity against Avicel increased on average 17.5 % at 65 °C and 16.4 % at 75 °C. CONCLUSIONS: Expression and secretion of E1 in C. bescii enhanced the cellulolytic ability of its secretome. These data agree with in vitro evidence that E1 acts synergistically with CelA to digest cellulose and offer the possibility of engineering additional enzymes for improved biomass deconstruction with the knowledge that C. bescii can express a gene from Acidothermus, and perhaps other heterologous genes, effectively.

Direct conversion of plant biomass to ethanol by engineered Caldicellulosiruptor bescii.

Ethanol is the most widely used renewable transportation biofuel in the United States, with the production of 13.3 billion gallons in 2012 [John UM (2013) Contribution of the Ethanol Industry to the Economy of the United States]. Despite considerable effort to produce fuels from lignocellulosic biomass, chemical pretreatment and the addition of saccharolytic enzymes before microbial bioconversion remain economic barriers to industrial deployment [Lynd LR, et al. (2008) Nat Biotechnol 26(2):169-172]. We began with the thermophilic, anaerobic, cellulolytic bacterium Caldicellulosiruptor bescii, which efficiently uses unpretreated biomass, and engineered it to produce ethanol. Here we report the direct conversion of switchgrass, a nonfood, renewable feedstock, to ethanol without conventional pretreatment of the biomass. This process was accomplished by deletion of lactate dehydrogenase and heterologous expression of a Clostridium thermocellum bifunctional acetaldehyde/alcohol dehydrogenase. Whereas wild-type C. bescii lacks the ability to make ethanol, 70% of the fermentation products in the engineered strain were ethanol [12.8 mM ethanol directly from 2% (wt/vol) switchgrass, a real-world substrate] with decreased production of acetate by 38% compared with wild-type. Direct conversion of biomass to ethanol represents a new paradigm for consolidated bioprocessing, offering the potential for carbon neutral, cost-effective, sustainable fuel production.

Isolation and bioinformatic analysis of a novel transposable element, ISCbe4, from the hyperthermophilic bacterium, Caldicellulosiruptor bescii.

Caldicellulosiruptor bescii is an anaerobic thermophilic bacterium of special interest for use in the consolidated bioprocessing of plant biomass to biofuels. In the course of experiments to engineer pyruvate metabolism in C. bescii, we isolated a mutant of C. bescii that contained an insertion in the L-lactate dehydrogenase gene (ldh). PCR amplification and sequencing of the ldh gene from this mutant revealed a 1,609-bp insertion that contained a single open reading frame of 479 amino acids (1,440 bp) annotated as a hypothetical protein with unknown function. The ORF is flanked by an 8-base direct repeat sequence. Bioinformatic analysis indicated that this ORF is part of a novel transposable element, ISCbe4, which is only intact in the genus Caldicellulosiruptor, but has ancient relatives that are present in degraded (and previously unrecognized) forms across many bacterial and archaeal clades.

Metabolic engineering of Caldicellulosiruptor bescii yields increased hydrogen production from lignocellulosic biomass.

BACKGROUND: Members of the anaerobic thermophilic bacterial genus Caldicellulosiruptor are emerging candidates for consolidated bioprocessing (CBP) because they are capable of efficiently growing on biomass without conventional pretreatment. C. bescii produces primarily lactate, acetate and hydrogen as fermentation products, and while some Caldicellulosiruptor strains produce small amounts of ethanol C. bescii does not, making it an attractive background to examine the effects of metabolic engineering. The recent development of methods for genetic manipulation has set the stage for rational engineering of this genus for improved biofuel production. Here, we report the first targeted gene deletion, the gene encoding lactate dehydrogenase (ldh), for metabolic engineering of a member of this genus. RESULTS: A deletion of the C. bescii L-lactate dehydrogenase gene (ldh) was constructed on a non-replicating plasmid and introduced into the C. bescii chromosome by marker replacement. The resulting strain failed to produce detectable levels of lactate from cellobiose and maltose, instead increasing production of acetate and H2 by 21-34% relative to the wild type and ΔpyrFA parent strains. The same phenotype was observed on a real-world substrate - switchgrass (Panicum virgatum). Furthermore, the ldh deletion strain grew to a higher maximum optical density than the wild type on maltose and cellobiose, consistent with the prediction that the mutant would gain additional ATP with increased acetate production. CONCLUSIONS: Deletion of ldh in C. bescii is the first use of recently developed genetic methods for metabolic engineering of these bacteria. This deletion resulted in a redirection of electron flow from production of lactate to acetate and hydrogen. New capabilities in metabolic engineering combined with intrinsic utilization of lignocellulosic materials position these organisms to provide a new paradigm for consolidated bioprocessing of fuels and other products from biomass.

Construction of a stable replicating shuttle vector for Caldicellulosiruptor species: use for extending genetic methodologies to other members of this genus.

The recalcitrance of plant biomass is the most important barrier to its economic conversion by microbes to products of interest. Thermophiles have special advantages for biomass conversion and members of the genus Caldicellulosiruptor are the most thermophilic cellulolytic microbes known. In this study, we report the construction of a replicating shuttle vector for Caldicellulosiruptor species based on pBAS2, the smaller of two native C. bescii plasmids. The entire plasmid was cloned into an E. coli cloning vector containing a pSC101 origin of replication and an apramycin resistance cassette for selection in E. coli. The wild-type C. bescii pyrF locus was cloned under the transcriptional control of the regulatory region of the ribosomal protein S30EA (Cbes2105), and the resulting vector was transformed into a new spontaneous deletion mutant in the pyrFA locus of C. bescii that allowed complementation with the pyrF gene alone. Plasmid DNA was methylated in vitro with a recently described cognate methyltransferase, M.CbeI, and transformants were selected for uracil prototrophy. The plasmid was stably maintained in low copy with selection but rapidly lost without selection. There was no evidence of DNA rearrangement during transformation and replication in C. bescii. A similar approach was used to screen for transformability of other members of this genus using M.CbeI to overcome restriction as a barrier and was successful for transformation of C. hydrothermalis, an attractive species for many applications. Plasmids containing a carbohydrate binding domain (CBM) and linker region from the C. bescii celA gene were maintained with selection and were structurally stable through transformation and replication in C. bescii and E. coli.

Cloning and sequence analysis of the heat-stable acrylamidase from a newly isolated thermophilic bacterium, Geobacillus thermoglucosidasius AUT-01.

A thermophilic bacterium capable of degrading acrylamide, AUT-01, was isolated from soil collected from a hot spring area in Montana, USA. The thermophilic strain grew with 0.2 % glucose as the sole carbon source and 1.4 mM acrylamide as the sole nitrogen source. The isolate AUT-01 was identified as Geobacillus thermoglucosidasius based on 16S rDNA sequence. An enzyme from the strain capable of transforming acrylamide to acrylic acid was purified by a series of chromatographic columns. The molecular weight of the enzyme was estimated to be 38 kDa by SDS-PAGE. The enzyme activity had pH and temperature optima of 6.2 and 70 ºC, respectively. The influence of different metals and amino acids on the ability of the purified protein to transform acrylamide to acrylic acid was evaluated. The gene from G. thermoglucosidasius encoding the acrylamidase was cloned, sequenced, and compared to aliphatic amidases from other bacterial strains. The G. thermoglucosidasius gene, amiE, encoded a 38 kDa, monomeric, heat-stable amidase that catalysed the cleavage of carbon-nitrogen bonds in acrylamide. Comparison of the amino acid sequence to other bacterial amidases revealed 99 and 82 % similarity to the amino acid sequences of Bacillus stearothermophilus and Pseudomonas aeruginosa, respectively.

Improved growth media and culture techniques for genetic analysis and assessment of biomass utilization by Caldicellulosiruptor bescii.

Methods for efficient growth and manipulation of relatively uncharacterized bacteria facilitate their study and are essential for genetic manipulation. We report new growth media and culture techniques for Caldicellulosiruptor bescii, the most thermophilic cellulolytic bacterium known. A low osmolarity defined growth medium (LOD) was developed that avoids problems associated with precipitates that form in previously reported media allowing the monitoring of culture density by optical density at 680 nm (OD(680)) and more efficient DNA transformation by electroporation. This is a defined minimal medium and does not support growth when a carbon source is omitted, making it suitable for selection of nutritional markers as well as the study of biomass utilization by C. bescii. A low osmolarity complex growth medium (LOC) was developed that dramatically improves growth and culture viability during storage, making it a better medium for routine growth and passaging of C. bescii. Both media contain significantly lower solute concentration than previously published media, allowing for flexibility in developing more specialized media types while avoiding the issues of growth inhibition and cell lysis due to osmotic stress. Plating on LOD medium solidified by agar results in ~1,000-fold greater plating efficiency than previously reported and allows the isolation of discrete colonies. These new media represent a significant advance for both genetic manipulation and the study of biomass utilization in C. bescii, and may be applied broadly across the Caldicellulosiruptor genus.

Characterization of Acrylamidase isolated from a newly isolated acrylamide-utilizing bacterium, Ralstonia eutropha AUM-01.

A mesophilic bacterium capable of utilizing acrylamide was isolated, AUM-01, from soil collected from leaf litter at Picnic Point on the UW-Madison campus. In minimal medium with acrylamide as the sole carbon and nitrogen source, a batch culture of AUM-01 completely converted 28.0 mM acrylamide to acrylic acid in 8 h and reached a cell density of 0.3 (A600)). Afterward all the acrylic acid was degraded by 20 h with the cell density increasing to 1.9 (A600). The acrylamide-utilizing bacterium was identified as Ralstonia eutropha based on morphological observations, the BiOLOG GN2 MicroPlate™ identification system for Gram-negative bacteria, and additional physiological tests. An acrylamidase that hydrolyzes acrylamide to acrylic acid was purified from the strain AUM-01. The molecular weight of the enzyme from AUM-01 was determined to be 38 kDa by SDS-PAGE. The enzyme had pH and temperature optima of 6.3 and 55°C, and the influence of different metals and amino acids on the ability of the purified protein to transform acrylamide to acrylic acid was evaluated. The enzyme from AUM-01 was totally inhibited by ZnSO4 and AgNO3.