Effects of gas condition on acetic acid fermentation by Clostridium thermocellum and Moorella thermoacetica (C. thermoaceticum)

Acetate Production from Syngas Produced from Lignocellulosic Biomass Materials along with Gaseous Fermentation of the Syngas: A Review

Biotransformation of lignocellulose-derived synthetic gas (syngas) into acetic acid is a promising way of creating biochemicals from lignocellulosic waste materials. Acetic acid has a growing market with applications within food, plastics and for upgrading into a wide range of biofuels and bio-products. In this paper, we will review the microbial conversion of syngas to acetic acid. This will include the presentation of acetate-producing bacterial strains and their optimal fermentation conditions, such as pH, temperature, media composition, and syngas composition, to enhance acetate production. The influence of syngas impurities generated from lignocellulose gasification will further be covered along with the means to alleviate impurity problems through gas purification. The problem with mass transfer limitation of gaseous fermentation will further be discussed as well as ways to improve gas uptake during the fermentation.

Advances and Applications of Clostridium Co-culture Systems in Biotechnology

Clostridium spp. are important microorganisms that can degrade complex biomasses such as lignocellulose, which is a widespread and renewable natural resource. Co-culturing Clostridium spp. and other microorganisms is considered to be a promising strategy for utilizing renewable feed stocks and has been widely used in biotechnology to produce bio-fuels and bio-solvents. In this review, we summarize recent progress on the Clostridium co-culture system, including system unique advantages, composition, products, and interaction mechanisms. In addition, biochemical regulation and genetic modifications used to improve the Clostridium co-culture system are also summarized. Finally, future prospects for Clostridium co-culture systems are discussed in light of recent progress, challenges, and trends.

Application of γ-PGA as the primary carbon source to bioremediate a TCE-polluted aquifer: A pilot-scale study

The effectiveness of using gamma poly-glutamic acid (γ-PGA) as the primary carbon and nitrogen sources to bioremediate trichloroethene (TCE)-contaminated groundwater was studied in this pilot-scale study. γ-PGA (40 L) solution was injected into the aquifer via the injection well (IW) for substrate supplement. Groundwater samples were collected from monitor wells and IW and analyzed for TCE and its byproducts, geochemical indicators, dechlorinating bacteria, and microbial diversity periodically. Injected γ-PGA resulted in an increase in total organic carbon (TOC) (up to 9820 mg/L in IW), and the TOC biodegradation caused the formation of anaerobic conditions. Increased ammonia concentration (because of amine release from γ-PGA) resulted in the neutral condition in groundwater, which benefited the growth of Dehalococcoides. The negative zeta potential and micro-scale diameter of γ-PGA allowed its globule to distribute evenly within soil pores. Up to 93% of TCE removal was observed (TCE dropped from 0.14 to 0.01 mg/L) after 59 days of γ-PGA injection, and TCE dechlorination byproducts were also biodegraded subsequently. Next generation sequence (NGS) analyses were applied to determine the dominant bacterial communities. γ-PGA supplement developed reductive dechlorinating conditions and caused variations in microbial diversity and dominant bacterial species. The dominant four groups of bacterial communities including dechlorinating bacteria, vinyl chloride degrading bacteria, hydrogen producing bacteria, and carbon biodegrading bacteria.

Microbial Degradation of Cellulosic Material and Gas Generation: Implications for the Management of Low- and Intermediate-Level Radioactive Waste

Deep geologic repositories (DGR) in Canada are designed to contain and isolate low- and intermediate-level radioactive waste. Microbial degradation of the waste potentially produces methane, carbon dioxide and hydrogen gas. The generation of these gases increase rock cavity pressure and limit water ingress which delays the mobility of water soluble radionuclides. The objective of this study was to measure gas pressure and composition over 7 years in experiments containing cellulosic material with various starting conditions relevant to a DGR and to identify micro-organisms generating gas. For this purpose, we conducted experiments in glass bottles containing (1) wet cellulosic material, (2) wet cellulosic material with compost Maker, and (3) wet cellulosic material with compost Accelerator. Results demonstrated that compost accelerated the pressure build-up in the containers and that methane gas was produced in one experiment with compost and one experiment without compost because the pH remained neutral for the duration of the 464 days experiment. Methane was not formed in the other experiment because the pH became acidic. Once the pressure became similar in all containers after 464 days, we then monitored gas pressure and composition in glass bottle containing wet cellulosic material in (1) acidic conditions, (2) neutral conditions, and (3) with an enzyme that accelerated degradation of cellulose over 1965 days. In these experiments, acetogenic bacteria degraded cellulose and produced acetic acid, which acidity suppressed methane production. Microbial community analyses suggested a diverse community of archaea, bacteria and fungi actively degrading cellulose. DNA analyses also confirmed the presence of methanogens and acetogens in our experiments. This study suggests that methane gas will be generated in DGRs if pH remains neutral. However, our results showed that microbial degradation of cellulose not only generated gas, but also generated acidity. This finding is important as acids can limit bentonite swelling and potentially degrade cement and rock barriers, thus this requires consideration in the safety case as appropriate.

Inducing effects of cellulosic hydrolysate components of lignocellulose on cellulosome synthesis in Clostridium thermocellum

Cellulosome is a highly efficient supramolecular machine for lignocellulose degradation, and its substrate‐coupled regulation requires soluble transmembrane signals. However, the inducers for cellulosome synthesis and the inducing effect have not been clarified quantitatively. Values of cellulosome production capacity (CPC) and estimated specific activity (eSA) were calculated based on the primary scaffoldin ScaA to define the stimulating effects on the cellulosome synthesis in terms of quantity and quality respectively. The estimated cellulosome production of Clostridium thermocellum on glucose was at a low housekeeping level. Both Avicel and cellobiose increased CPCs of the cells instead of the eSAs of the cellulosome. The CPC of Avicel‐grown cells was over 20‐fold of that of glucose‐grown cells, while both Avicel‐ and glucose‐derived cellulosomes showed similar eSA. The CPC of cellobiose‐grown cells was also over three times higher than glucose‐grown cells, but the eSA of cellobiose‐derived cellulosome was 16% lower than that of the glucose‐derived cellulosome. Our results indicated that cello‐oligosaccharides played the key roles in inducing the synthesis of the cellulosome, but non‐cellulosic polysaccharides showed no inducing effects.