Aerobic Hydrogen Production via Nitrogenase in Azotobacter vinelandii CA6

Abstract

The diazotroph Azotobacter vinelandii possesses three distinct nitrogenase isoenzymes, all of which produce molecular hydrogen as a by-product. In batch cultures, A. vinelandii strain CA6, a mutant of strain CA, displays multiple phenotypes distinct from its parent: tolerance to tungstate, impaired growth and molybdate transport, and increased hydrogen evolution. Determining and comparing the genomic sequences of strains CA and CA6 revealed a large deletion in CA6's genome, encompassing genes related to molybdate and iron transport and hydrogen reoxidation. A series of iron uptake analyses and chemostat culture experiments confirmed iron transport impairment and showed that the addition of fixed nitrogen (ammonia) resulted in cessation of hydrogen production. Additional chemostat experiments compared the hydrogen-producing parameters of different strains: in iron-sufficient, tungstate-free conditions, strain CA6's yields were identical to those of a strain lacking only a single hydrogenase gene. However, in the presence of tungstate, CA6 produced several times more hydrogen. A. vinelandii may hold promise for developing a novel strategy for production of hydrogen as an energy compound.

Natural hydrogen continuous emission from sedimentary basins: The example of a Brazilian H2-emitting structure

“…Concerning possible hydrogen sources, three main processes are envisioned (1) degassing from an original material [16] (2) water source rock interactions (i.e. REDOX chemical processes [23], or water destruction through radiolysis e [19]or crystal cracking e [42] and (3) bacterial origin [31,32]. Migration, carrier beds and reservoirs include most rocks containing a minimum of porosity and permeability.…”

“…In literature, soils are always considered as hydrogen sinks with atmospheric hydrogen concentration around 0.5 ppm, mainly generated by photoproduction from H 2 O and CH 4 [3], and is being consumed by microbial life in soils [7,8,14,34,40]. It is extensively referenced that microbiology in soils also generates molecular hydrogen, as the first source of energy for life without possibility of photosynthesis [31]. However, the measured concentrations from biological culture of nitrogenase organisms are generally minor (in the best case scenario, [31]; measure 90 ppm in their experiments, without any posterior biological consumption of the generated H 2 ).…”

“…It is extensively referenced that microbiology in soils also generates molecular hydrogen, as the first source of energy for life without possibility of photosynthesis [31]. However, the measured concentrations from biological culture of nitrogenase organisms are generally minor (in the best case scenario, [31]; measure 90 ppm in their experiments, without any posterior biological consumption of the generated H 2 ). The absence of measurable CO 2 (as reported from the GA5000 © portable gas analyzer) associated with H 2 (which would possibly indicate a biological respiration) and the observation of above atmospheric (5 ppm) helium concentrations favors the marginal effect of biological hydrogen generation.…”

Azotobacter vinelandii Nitrogenase Activity, Hydrogen Production, and Response to Oxygen Exposure

“…Strain CA6 was previously sequenced and characterized by our group to understand why these strains show a deregulated nitrogenase phenotype. This analysis revealed a large ϳ42-kb deletion encompassing the molybdate uptake operon, several regulation operons, and the entire uptake hydrogenase operon (45,46). The same 42-kb deletion is also present in strain CA11.6.…”

“…The same 42-kb deletion is also present in strain CA11.6. Without the uptake hydrogenase operon, these strains have the same hydrogen-producing phenotype driven by nitrogenase activity as the hoxK knockout mutants (45). Therefore, hydrogen gas released by cells growing under nitrogen fixing conditions can be used as a means to estimate the in vivo nitrogenase activity of each isoenzyme under various oxygen exposure conditions.…”