Growth of Rhodospirillum rubrum on synthesis gas: Conversion of CO to H₂ and poly‐β‐hydroxyalkanoate

Abstract

To examine the potential use of synthesis gas as a carbon and energy source in fermentation processes, Rhodospirillum rubrum was cultured on synthesis gas generated from discarded seed corn. The growth rates, growth and poly-beta-hydroxyalkanoates (PHA) yields, and CO oxidation/H(2) evolution rates were evaluated in comparison to the rates observed with an artificial synthesis gas mixture. Depending on the gas conditioning system used, synthesis gas either stimulated or inhibited CO-oxidation rates compared to the observations with the artificial synthesis gas mixture. Inhibitory and stimulatory compounds in synthesis gas could be removed by the addition of activated charcoal, char-tar, or char-ash filters (char, tar, and ash are gasification residues). In batch fermentations, approximately 1.4 mol CO was oxidized per day per g cell protein with the production of 0.75 mol H(2) and 340 mg PHA per day per g cell protein. The PHA produced from R. rubrum grown on synthesis gas was composed of 86% beta-hydroxybutyrate and 14% beta-hydroxyvalerate. Mass transfer of CO into the liquid phase was determined as the rate-limiting step in the fermentation.

Enhancing CO−Water Mass Transfer by Functionalized MCM41 Nanoparticles

“…[1][2][3][4] Therefore, syngas fermentation is a potential pathway for converting biomass to a variety of fuels and chemicals because of its low cost and potentially high efficiency. The actual conversion efficiency depends on the microorganism and the desired product but can easily be 35% or higher.…”

Heterologous Expression of Various PHA Synthase Genes in Rhodospirillum rubrum

“…Cultivations were carried out under heterotrophic and autotrophic conditions as well as in the absence or presence of light 14,15,16,18,42,43 . In most preceding studies, R. rubrum showed slow growth rates leading to long and inefficient cultivations.…”

“…One promising and widely investigated approach is the utilization of industrial waste products 13 . Besides complex industrial wastes, gasification processes enable the conversion of any carbonaceous material into synthesis gas (syngas) 13,14,15 . Syngas mainly consists of The phototrophic non-sulfur purple bacterium Rhodospirillum rubrum is known for its metabolic versatility.…”

“…hydrogen (H 2 ), carbon monoxide (CO) and carbon dioxide (CO 2 ), and has attracted great biotechnical interest as a cheap but undefined feedstock for the fermentation of various microorganisms in the last years 14 . The phototrophic non-sulfur purple bacterium Rhodospirillum rubrum is able to synthesize PHA under heterotrophic and even autotrophic growth with carbon monoxide (CO) and carbon dioxide (CO 2 ) as carbon and energy source 14,15 .…”

“…The phototrophic non-sulfur purple bacterium Rhodospirillum rubrum is able to synthesize PHA under heterotrophic and even autotrophic growth with carbon monoxide (CO) and carbon dioxide (CO 2 ) as carbon and energy source 14,15 . Growth of Rhodospirillum rubrum utilizing syngas has already been intensively investigated 14,15,16 . In 2008, a profitable and technically feasible concept for PHA accumulation of R. rubrum based on the utilization of synthesis gas was presented for the first time 16 .…”