How is acetogenesis a facultative change in metabolism?
In environments with efficient H 2 sinks, such as anaerobic digesters, many of the acidogenic species direct their metabolism to acetogenesis. This facultative change in metabolism has been demonstrated in defined methanogenic co-cultures degrading alcohols, lactate, pyruvate, cellobiose, glucose, fructose, and cellulose [9].
What kind of bacteria are involved in acetogenesis?
A thermophilic butyrate-degrading species growing in association with Methanobacterium thermoautotrophicum has been described. Methanogenesis from long-chain fatty acids and 3-chlorobenzoic acid is also thought to involve obligately proton-reducing acetogenic bacteria.
Which is not obligately reducing protons during acetogenesis?
Acetogenesis species can be subdivided into those that are not obligately proton-reducing, that is, hydrogen-producing, species and those that do reduce protons to hydrogen obligately during acetogenesis.
Are there any obligate proton-reducing acetogens in axenic culture?
Other obligate proton-reducing acetogens have been described: Syntrophobacter wolinii degrades propionate, Syntrophomonas wolfei degrades butyrate, and Syntrophus buswellii degrades benzoate [9]. Conditions may yet be found which support the growth of the acetogens in axenic culture.
How are organic acids oxidized to acetate in acetogenesis?
These bacteria compete with methanogens for substrates like hydrogen, formate, and methanol. Organic acids (such as propionate and butyrate) and alcohols (such as ethanol) produced during the fermentation step are oxidized to acetate by hydrogen-producing acetogens.
How are acetogenic bacteria dependent on methanogenic archaea?
This results in an obligate dependence of acetogenic bacteria on methanogenic archaea or other hydrogen scavengers (e.g., sulfate reducers) for product removal ( McInerney et al., 2008; Sousa et al., 2009; Stams and Plugge, 2009 ).
What are the conditions for acetogenesis in axenic culture?
Conditions may yet be found which support the growth of the acetogens in axenic culture. For example, Syntrophococcus sucromutants grows well in mutualistic co-culture with a methanogen but some organic electron acceptors support its growth in pure culture.
