Tolerance and Metabolic Response of Acetogenic Bacteria toward Oxygen

Abstract

The acetogens Sporomusa silvacetica, Moorella thermoacetica, Clostridium magnum, Acetobacterium woodii, and Thermoanaerobacter kivui (i) grew in both semisolid and liquid cultivation media containing O 2 and (ii) consumed small amounts of O 2 . Low concentrations of O 2 caused a lag phase in growth but did not alter the ability of these acetogens to synthesize acetate via the acetyl coenzyme A pathway. Cell extracts of S. silvacetica, M. thermoacetica, and C. magnum contained peroxidase and NADH oxidase activities; catalase and superoxide dismutase activities were not detected.Acetogens have been termed obligate or strict anaerobes. They do not grow aerobically, are isolated mostly from anoxic habitats, and utilize a pathway (the acetyl coenzyme A pathway) that contains enzymes that are extremely sensitive to O 2 (6, 7, 22). However, acetogens (i) can be readily isolated from leaf litter and the mineral soil of well-drained, oxic soils (8, 9), (ii) can tolerate periods of oxygenation in soils (21), (iii) are active in termite guts that have steep oxygen gradients (20), and (iv) occur in high numbers in transiently oxygenated rhizosphere sediments colonized by sea grass (12). These observations suggest that certain acetogens must cope with O 2 under in situ conditions. In preliminary studies, the classic acetogen Moorella thermoacetica was found to reduce resazurin in O 2 -supplemented medium (A. Gößner and H. L. Drake, unpublished data), and the objective of the present study was to determine the tolerance and metabolic response of model acetogens toward O 2 (for a preliminary report of this study, see A. Karnholz, K. Küsel, and H. L. Drake, Abstr. 100th Gen. Meet. Am. Soc. Microbiol. 2000, abstr. I-91, p. 401, 2000.Organisms, media, and growth conditions. The acetogens used in this study were selected because each is a well-described model acetogen that has been isolated from a different habitat. The temperatures of incubation for Sporomusa silvacetica (DSM 10669; isolated from soil), M. thermoacetica (DSM 1974; isolated from horse manure), Clostridium magnum (DSM 2767; isolated from fresh water sediment), Acetobacterium woodii (DSM 1030; isolated from a marine estuary), and Thermoanaerobacter kivui (DSM 2030; isolated from lake sediment) were 30, 55, 30, 30, and 55°C, respectively. The acetogens were cultivated in a carbonate-buffered, undefined (U) medium containing yeast extract, vitamins, and trace metals but no reducing agents (4). Medium was dispensed under CO 2 into 27-ml crimp seal culture tubes (7 ml of medium per tube) or 1-liter infusion bottles (500 ml of medium per bottle; used for preparation of cell extracts), which were then sealed and autoclaved; the pH was approximately 6.7. Anoxic aqueous stock solutions of glucose or fructose (prepared under argon) were filter sterilized and added to the medium by syringe injection by using O 2 -free techniques. Culture tubes and bottles containing liquid medium were incubated in a horizontal, static position. Culture tubes were shaken vigorously before opt...

Chemolithotrophic acetogenic H2/CO2 utilization in Italian rice field soil

“…H 2 -CO 2 , formate, methanol and a few other compounds serve as substrates, and acetate is the sole reduced end product. C. magnum can assimilate N 2 (Bomar et al, 1991) and tolerate and consume small amounts of O 2 (Karnholz et al, 2002). Growth is possible at 15-45 1C with the optimum at 30-32 1C.…”

Commercial Biomass Syngas Fermentation

“…Kawasaki et al found that the peptide transcripts of A-type flavoprotein homologue and novel type rubrerythrin homologue in C. acetobutylicum were upregulated within ten minutes of an oxygen shock [246]. Other enzymes thought to be involved in oxygen metabolism in acetogens include NADH-oxidase, superoxide dismutase, and rubrerythrin [244,247]. Karnholz et al found that acetogens including M. thermoacetica and A. woodii grew in non-reduced liquid medium containing small amounts of O 2 gas; furthermore, they found that increasing this amount of O 2 caused an increase in the lag growth phase, with a decrease in final biomass achieved [244].…”

“…For example, pyruvate-ferredoxin oxidoreductase catalyses a pyruvate-CO 2 exchange reaction: its exposed iron-sulphur sites are susceptible to oxidative inactivation, leading it to be one of the most oxygen sensitive enzymes known [121,242,243]. Interestingly, some acetogens have an oxygen detoxification pathway which allows them to tolerate certain levels of oxidative stress [244]. This has been demonstrated physiologically throughout the Clostridium genus, with species such as Clostridium butyricum and C. acetobutylicum being shown to resume growth following oxygen consumption, with no lasting damage.…”

Clostridium straminisolvens sp. nov., a moderately thermophilic, aerotolerant and cellulolytic bacterium isolated from a cellulose-degrading bacterial community

“…In contrast, C. thermocellum (IAM 13660 T ) could not grow in an atmosphere containing an O 2 concentration of more than 2 %. In the genus Clostridium, some species that can grow in an atmosphere containing an O 2 concentration of up to 6 % have been reported, and the species have the ability to consume O 2 (Küsel et al, 2001;Karnholz et al, 2002). Colour changing of resazurin in the media indicated that strain CSK1 T consumes O 2 during cultivation in an atmosphere containing O 2 .…”