Effect of CO2 on the fermentation capacities of the acetogen Peptostreptococcus productus U-1

Abstract

The fermentative capacities of the acetogenic bacterium Peptostreptococcus productus U-1 (ATCC 35244) were examined. Although acetate was formed from all the substrates tested, additional products were produced in response to CO 2 limitation. Under CO 2 -limited conditions, fructose-dependent growth yielded high levels of lactate as a reduced end product; lactate was also produced under CO 2 -enriched conditions when fructose concentrations were elevated. In the absence of supplemental CO 2 , xylose-dependent growth yielded lactate and succinate as major reduced end products. Although supplemental CO 2 and acetogenesis stimulated cell yields on fructose, xylose-dependent cell yields were decreased in response to CO 2 and acetogenesis. In contrast, glycerol-dependent growth yielded high levels of ethanol in the absence of supplemental CO 2 , and pyruvate was subject to only acetogenic utilization independent of CO 2 . CO 2 pulsing during the growth of CO 2 -limited fructose cultures stopped lactate synthesis immediately, indicating that CO 2 -limited cells were nonetheless metabolically poised to respond quickly to exogenous CO 2 . Resting cells that were cultivated at the expense of fructose without supplemental CO 2 readily consumed fructose in the absence of exogenous CO 2 and formed only lactate. Although the specific activity of lactate dehydrogenase was not appreciably influenced by supplemental CO 2 during cultivation, cells cultivated on fructose under CO 2 -enriched conditions displayed minimal capacities to consume fructose in the absence of exogenous CO 2 . These results demonstrate that the utilization of alternative fermentations for the conservation of energy and growth of P. productus U-1 is augmented by the relative availability of CO 2 and growth substrate.Acetogenic bacteria utilize CO 2 as a terminal electron acceptor and synthesize acetate by the acetyl coenzyme A (acetyl-CoA) Wood/Ljungdahl pathway (12,16,35,36,44). The reduction of CO 2 to acetate is coupled to respiratory conservation of energy via either membranous electron transport or sodium pumping systems (11,27,33). Although supplemental CO 2 can be essential or greatly stimulatory to acetogenesis under certain conditions, acetogens can use other respiratory reductant sinks (15,17,18), including aromatic acrylate groups (2,22,32,40), fumarate (13, 31), dimethyl sulfoxide (3), and nitrate (20,37).In contrast to the numerous studies that have evaluated the respiratory capacities of acetogens, the fermentation capacities of this bacteriological group have been minimally examined. Indeed, although certain acetogens can form fermentative end products such as ethanol (8, 39), acetogens are commonly thought to route the reductant derived from glycolysis toward the respiration of CO 2 to acetate (12,16,44). The acetogenic sewage isolate Peptostreptococcus productus U-1 has been reported to form lactate (28). Although lactate production by P. productus U-1 has not been quantitatively examined, preliminary studies in our laboratory indicated th...

Metabolic modelling of syntrophic-like growth of a 1,3-propanediol producer, Clostridium butyricum, and a methanogenic archeon, Methanosarcina mazei, under anaerobic conditions

“…Acetogens or many heterotrophic sulphate reducers excrete hydrogen and carbon dioxide or acetic and formic acid, which are immediately utilised by methanogens [5][6][7][8]. Both species profit, as, for example, hydrogen is an inhibitor for acetogenic and sulphate-reducing bacteria.…”

Formate-Dependent Growth and Homoacetogenic Fermentation by a Bacterium from Human Feces: Description of Bryantella formatexigens gen. nov., sp. nov

“…Drake (6) pointed out that acetogenesis by most acetogens is conditional and depends on the availability of a reductant and a terminal electron acceptor, including CO 2. The acetogen Peptostreptococcus productus U-1 produces lactate, succinate, and acetate under CO 2 -limited conditions, and CO 2 enrichment increases acetate formation and decreases the formation of lactate and succinate (7,19). Batch growth of strain I-52…”

Transient Production of Formate During Chemolithotrophic Growth of Anaerobic Microorganisms on Hydrogen

“…Escherichia coli and related enterobacteria possess a formate-hydrogen lyase enzyme system that catalyzes the reversible conversion of formate to H 2 plus CO 2 [4,29]. Formate is also known to be a product when homoacetogenic bacteria are grown on hexoses, for example, Clostridium aceticum [16], Clostridium formicoaceticum, [1] and Peptostreptococcus productus [27]. Formate instead of H 2 is often produced when syntrophic bacteria grow on organic acids and alcohols, and then replaces H 2 in the so-called interspecies-formate-transfer to methanogenic archaea [5,13,34].…”