Laura Dipasquale

The effect of the surface charge of hydrogel supports on thermophilic biohydrogen production.

The effect of the surface charge of different immobilizing hydrogels on biohydrogen production in batch cultures was investigated using a novel isolate associated to the genus Thermoanaerobacterium. Two crosslinked polysaccharide-based hydrogels and two acrylic hydrogels were tested as polymeric carriers for cell adsorption. Immobilization improved both substrate conversion and hydrogen cumulative production compared to the suspended culture, and a yield of 1.9 mol H(2)/mol glucose was observed after 24h for alginate-supported cultures. Cationic carriers dramatically increased cell immobilization, leading to markedly faster kinetics of substrate degradation and hydrogen production in batch operation, with a peak of 3.6 mol H(2)/mol glucose for the acrylic hydrogel HM92. Accumulation of gaseous and acidic metabolites inhibited further H(2) production, shifting the carbon flow to reduced end-products and biomass synthesis. Preliminary tests showed that all the tested hydrogels had good durability and allowed hydrogen production on repeated batch runs.

Hydrogen Production by the Thermophilic Bacterium Thermotoga neapolitana

As the only fuel that is not chemically bound to carbon, hydrogen has gained interest as an energy carrier to face the current environmental issues of greenhouse gas emissions and to substitute the depleting non-renewable reserves. In the last years, there has been a significant increase in the number of publications about the bacterium Thermotoga neapolitana that is responsible for production yields of H2 that are among the highest achievements reported in the literature. Here we present an extensive overview of the most recent studies on this hyperthermophilic bacterium together with a critical discussion of the potential of fermentative production by this bacterium. The review article is organized into sections focused on biochemical, microbiological and technical issues, including the effect of substrate, reactor type, gas sparging, temperature, pH, hydraulic retention time and organic loading parameters on rate and yield of gas production.

Continuous hydrogen production by immobilized cultures of Thermotoga neapolitana on an acrylic hydrogel with pH-buffering properties

This communication reports on the continuous biohydrogen production by Thermotoga neapolitana cells immobilized on a stable cationic hydrogel bearing amine groups. This hydrogel was designed to perform two functional activities: to promote adhesion of T. neapolitana cells, and to buffer pH changes in the bacterial cultures. Repeated fed-batch cultures showed an average hydrogen production rate and yield of 50.6 mL L−1 h−1 and 3.3 mol H2/mol glucose, respectively. To the best of our knowledge, this is the first report detailing the immobilization of this bacterial strain on a polymeric support.

Recycling of Carbon Dioxide and Acetate as Lactic Acid by the Hydrogen‐Producing Bacterium Thermotoga neapolitana

The heterotrophic bacterium Thermotoga neapolitana produces hydrogen by fermentation of sugars. Under capnophilic (carbon dioxide requiring) conditions, the process is preferentially associated with the production of lactic acid, which, as shown herein, is synthesized by reductive carboxylation of acetyl coenzyme A. The enzymatic coupling is dependent on the carbon dioxide stimulated activity of heterotetrameric pyruvate:ferredoxin oxidoreductase. Under the same culture conditions, T. neapolitana also operates the unfavorable synthesis of lactic acid from an exogenous acetate supply. This process, which requires carbon dioxide (or carbonate) and an unknown electron donor, allows for the conversion of carbon dioxide into added-value chemicals without biomass deconstruction.

Purification and characterisation of a highly thermostable extracellular protease fromBacillus thermantarcticus, strain M1

A high thermostable extracellular protease was purified to homogeneity and characterised fromBacillus thermantarcticus, strain M1. The molecular mass was about 42 kDa. Almost total inhibition of protease by phenyl methyl sulphonylfluoride (PMSF), suggested that the enzyme belonged to the serine protease family. The enzyme was active and stable in a broad range of pH with an optimum at pH 7.0. The protease showed the highest activity at 70°C and was stable for 24 h at 70°C, with an increase of the enzymatic activity of about 4 times, in the presence of CaCl2. The protease retained about 50% activity after 3 h of incubation in the presence of CaCl2 with various commercial detergents. Purified protease was found to be stable, for one week, in presence of DMSO, methanol, ethanol, acetonitrile, isopropanol.

Potential of Hydrogen Fermentative Pathways in Marine Thermophilic Bacteria: Dark Fermentation and Capnophilic Lactic Fermentation in Thermotoga and Pseudothermotoga Species

Hydrogen is a clean energy vector that could help to face the current environmental issues of greenhouse gas emissions and, over a longer time scale, to replace the depleting nonrenewable fuels. Biological production by fermentation of waste and residues has the potential to surrogate the current technologies of production of this gas. In this chapter we report a summary of the fermentative pathways related to hydrogen production in the thermophilic microorganisms of the genera Thermotoga and Pseudothermotoga that embrace several marine species with the highest hydrogen yields among eubacteria. The contribution includes a brief review of dark fermentation (DF) and capnophilic lactic fermentation (CLF), the two processes related to hydrogen synthesis in these organisms, together with a discussion of new data concerning the distribution of CLF in these bacteria. The data show a varied scenario with different metabolic capabilities spread across the two genera. Under standard conditions, CLF is active only in few species of Thermotoga genus. The study underlines the great potential of these microbes in the valorization of agro-food waste and production of fuel and chemicals. In particular, the metabolic and biochemical diversity of Thermotoga and Pseudothermotoga species, together with their resilience to different environmental conditions, suggests the possibility to overtake many of the bottlenecks related to operational factors such as substrates, temperature, pH, hydraulic retention time, and hydrogen partial pressure.