There is an immediate need to drastically reduce the emissions associated with global fossil fuel consumption in order to limit climate change. However, carbon-based materials, chemicals, and transportation fuels are predominantly made from fossil sources and currently there is no alternative source available to adequately displace them. Gas-fermenting microorganisms that fix carbon dioxide (CO2) and carbon monoxide (CO) can break this dependence as they are capable of converting gaseous carbon to fuels and chemicals. As such, the technology can utilize a wide range of feedstocks including gasified organic matter of any sort (e.g., municipal solid waste, industrial waste, biomass, and agricultural waste residues) or industrial off-gases (e.g., from steel mills or processing plants). Gas fermentation has matured to the point that large-scale production of ethanol from gas has been demonstrated by two companies. This review gives an overview of the gas fermentation process, focusing specifically on anaerobic acetogens. Applications of synthetic biology and coupling gas fermentation to additional processes are discussed in detail. Both of these strategies, demonstrated at bench-scale, have abundant potential to rapidly expand the commercial product spectrum of gas fermentation and further improve efficiencies and yields.

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Gas Fermentation—A Flexible Platform for Commercial Scale Production of Low-Carbon-Fuels and Chemicals from Waste and Renewable Feedstocks

The feasibility of replacing yeast extract (YE) by corn steep liquor (CSL), a low cost nutrient source, for syngas fermentation to produce ethanol using Clostridium strain P11 was investigated. About 32% more ethanol (1.7 g L(-1)) was produced with 20 g L(-1) CSL media in 250-mL bottle fermentations compared to media with 1 g L(-1) YE after 360 h. Maximum ethanol concentrations after 360 h of fermentation in a 7.5-L fermentor with 10 and 20 g L(-1) CSL media were 8.6 and 9.6 g L(-1), respectively, which represent 57% and 60% of the theoretical ethanol yields from CO. Only about 6.1 g L(-1) of ethanol was obtained in the medium with 1 g L(-1) YE after 360 h, which represents 53% of the theoretical ethanol yield from CO. The use of CSL also enhanced butanol production by sevenfold compared to YE in bottle fermentations. These results demonstrate that CSL can replace YE as the primary medium component and significantly enhance ethanol production by Clostridium strain P11.

Ethanol Production from Syngas by Clostridium Strain P11 Using Corn Steep Liquor as a Nutrient Replacement

Bioethanol production from corn is a well-established technology. However, emphasis on exploring non-food based feedstocks is intensified due to dispute over utilization of food based feedstocks to generate bioethanol. Chemical and biological conversion technologies for non-food based biomass feedstocks to biofuels have been developed. First generation bioethanol was produced from sugar based feedstocks such as corn and sugar cane. Availability of alternative feedstocks such as lignocellulosic and algal biomass and technology advancement led to the development of complex biological conversion processes, such as separate hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF), simultaneous saccharification and co-fermentation (SSCF), consolidated bioprocessing (CBP), and syngas fermentation. SHF, SSF, SSCF, and CBP are direct fermentation processes in which biomass feedstocks are pretreated, hydrolyzed and then fermented into ethanol. Conversely, ethanol from syngas fermentation is an indirect fermentation that utilizes gaseous substrates (mixture of CO, CO2 and H2) made from industrial flue gases or gasification of biomass, coal or municipal solid waste. This review article provides an overview of the various biological processes for ethanol production from sugar, lignocellulosic, and algal biomass. This paper also provides a detailed insight on process development, bioreactor design, and advances and future directions in syngas fermentation.

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A review of conversion processes for bioethanol production with a focus on syngas fermentation

BACKGROUND: Ethanol production from synthesis gas (syngas) by Clostridium ljungdahlii was autotrophically carried out in a continuous flow stirred tank bioreactor (CSTR). A 2 L bioreactor was operated at 37 °C and constant agitation rate of 500 rpm. The experiments were conducted at various media flow rates and uncontrolled culture pH condition while the gas flow rate was kept constant at 14 mL min−1.

RESULTS: Continuous fermentation of the syngas containing 55% CO, 20% H2, 10% CO2 and 15% argon as internal standard resulted in cell dry weight of 2.34 g L−1 and CO conversion of 93%. Maximum concentration of ethanol and acetate was 6.50 g EthOH L−1 and 5.43 g Ac L−1.

CONCLUSION: High ethanol concentration was achieved in continuous fermentation using C. ljungdahlii. The ethanol producing ability of this acetogene and succesful switch of the metabolic pathway from acetogenesis to solventogenesis during the fermentation process was confirmed. Copyright © 2012 Society of Chemical Industry

Sustainable ethanol fermentation from synthesis gas by Clostridium ljungdahlii in a continuous stirred tank bioreactor

Fermentative production of ethanol from syngas using novel moderately alkaliphilic strains of Alkalibaculum bacchi.

The effect of dithiothreitol (DTT) on enhancing ethanol production from syngas using Clostridium strain P11 was investigated in 250-mL serum bottles. Reducing agents help in regeneration of NADH from NAD+. NADH is utilized in the production of alcohol from aldehydes. Strain P11 was fed with syngas every 24 h and samples were collected to measure pH, cell mass and product concentrations. Various concentrations of DTT were examined. Results showed over fourfold increase in ethanol production in media that contained at least 7.5 g/L of DTT after 360 h of fermentation compared to the control medium (without DTT). Similar pH, cell mass and acetic acid profiles were observed in the control and DTT media. The results suggested that the use of small concentrations of DTT in the broth enhances ethanol production from syngas, which is an important factor towards making gasification-fermentation technology an economically viable process.

Effect of the Reducing Agent Dithiothreitol on Ethanol and Acetic Acid Production by Clostridium Strain P11

Novel cationic-chalcone phthalocyanines for photodynamic therapy eradication of S. aureus and E. coli bacterial biofilms and MCF-7 breast cancer.

Meso-tetra(4-methylthiolphenyl)chlorin (3) and its Sn(IV) complex (3-Sn) have been synthesized and characterized. The heavy atom effects of the Sn(IV) ion and sulfur atoms result in relatively high singlet oxygen quantum yield values of 0.40 and 0.48. The photodynamic activities against MCF-7 breast cancer cells were determined through irradiation with a Thorlabs 660 nm LED for 30 min (280 mW.cm-2 ). IC50 values of 7.8 and 3.9 μM were obtained, respectively. 3-Sn was found to have significant photodynamic antimicrobial activity against both gram-(+) S. aureus and gram-(-) E. coli bacteria upon irradiation with a Thorlabs 660 nm LED for 75 min.

Photodynamic Antitumor and Antimicrobial Activities of Free-Base Tetra(4-methylthiolphenyl)chlorin and Its Tin(IV) Complex.

http://manuscript.elsevier.com/S0956713521009300/pdf/S0956713521009300.pdf

Prescreening veterinary drug residues, heavy metal concentration, and genetic authentication in retail catfish fillets in the Northeast United States

Two A2B type H3corroles and two GaIIItriarylcorroles with carbazole substitutions at 10-positions were synthesized and characterized. An analysis of structure-property relationships of the corroles has been carried out by investigating the optical spectroscopy of the dyes to trends predicted in DFT and TD-DFT calculations. Interestingly, the photodynamic therapy (PDT) and photodynamic antimicrobial chemotherapy (PACT) activity properties of the GaIIItriarylcorroles were determined against the MCF-7 breast cancer line, and Staphyloccocus aureus (S. aureus) and Escherichia coli (E. coli), respectively. The cationic G-2Q species exhibited the most favorable properties with an IC50 value of 7.8 μM against MCF-7 cells, and Log reduction values of 7.78 and 3.26 against planktonic S. aureus and E. coli at 0.5 and 10 μM, respectively.

Balaji Kubandra Babu

Papers

Effect of the Reducing Agent Dithiothreitol on Ethanol and Acetic Acid Production by Clostridium Strain P11

Novel cationic-chalcone phthalocyanines for photodynamic therapy eradication of S. aureus and E. coli bacterial biofilms and MCF-7 breast cancer.

Photodynamic Antitumor and Antimicrobial Activities of Free-Base Tetra(4-methylthiolphenyl)chlorin and Its Tin(IV) Complex.

Prescreening veterinary drug residues, heavy metal concentration, and genetic authentication in retail catfish fillets in the Northeast United States

GaIIItriarylcorroles with push-pull substitutions: synthesis, electronic structure and biomedical applications.