Production and consumption of nitrous oxide in nitrate-ammonifying Wolinella succinogenes cells.

Global warming is moving more and more into the public consciousness. Besides the commonly mentioned carbon dioxide and methane, nitrous oxide (N2O) is a powerful greenhouse gas in addition to its contribution to depletion of stratospheric ozone. The increasing concern about N2O emission has focused interest on underlying microbial energy-converting processes and organisms harbouring N2O reductase (NosZ), such as denitrifiers and ammonifiers of nitrate and nitrite. Here, the epsilonproteobacterial model organism Wolinella succinogenes is investigated with regard to its capacity to produce and consume N2O during growth by anaerobic nitrate ammonification. This organism synthesizes an unconventional cytochrome c nitrous oxide reductase (cNosZ), which is encoded by the first gene of an atypical nos gene cluster. However, W. succinogenes lacks a nitric oxide (NO)-producing nitrite reductase of the NirS- or NirK-type as well as an NO reductase of the Nor-type. Using a robotized incubation system, the wild-type strain and suitable mutants of W. succinogenes that either produced or lacked cNosZ were analysed as to their production of NO, N2O and N2 in both nitrate-sufficient and nitrate-limited growth medium using formate as electron donor. It was found that cells growing in nitrate-sufficient medium produced small amounts of N2O, which derived from nitrite and, most likely, from the presence of NO. Furthermore, cells employing cNosZ were able to reduce N2O to N2. This reaction, which was fully inhibited by acetylene, was also observed after adding N2O to the culture headspace. The results indicate that W. succinogenes cells are competent in N2O and N2 production despite being correctly grouped as respiratory nitrate ammonifiers. N2O production is assumed to result from NO detoxification and nitrosative stress defence, while N2O serves as a terminal electron acceptor in anaerobic respiration. The ecological implications of these findings are discussed.

Antimicrobial activity of flurbiprofen and ibuprofen in vitro against six common periodontal pathogens.

Nonsteroidal antiinflammatory drugs (NSAIDs) such as flurbiprofen and ibuprofen, have been shown to inhibit the inflammation and alveolar bone loss associated with chronic destructive periodontal disease. However, the direct effect of NSAIDs on the gingival crevice microflora has not been studied. The purpose of this investigation was to evaluate the antimicrobial activity of ibuprofen and flurbiprofen in vitro on six commonly isolated periodontal pathogens. The bacterial strains evaluated were Actinobacillus actinomycetemcomitans, Bacteroides gingivalis, Bacteroides intermedius, Eikenella corrodens, Fusobacterium nucleatum and Wolinella recta. Pure cultures of these organisms were inoculated into broth, allowed to grow and inoculated again into sheep blood agar plates. For preliminary dose-response studies, antibiotic sensitivity blank disks loaded with 10 microliters of flurbiprofen 250 micrograms, 50 micrograms and 5 micrograms, or ibuprofen 500 micrograms, 50 micrograms and 5 micrograms were placed on the seeded agar plates. Clindamycin 2 micrograms disks were used as positive controls and discs loaded with only drug vehicle served as negative controls. In an attempt to estimate the minimal inhibitory concentrations of these NSAIDs on specific microorganisms, additional experiments employing intermediate drug dosages were also performed. Clindamycin produced large zones of inhibition for all bacterial strains except for Eikenella corrodens which is known to be resistant to the antibiotic and Actinobacillus actinomycetemcomitans which appeared to be only moderately sensitive to the antibiotic. Zones of inhibition were not produced by any of the negative control disks or by the 5 micrograms or 50 micrograms doses of either NSAID.(ABSTRACT TRUNCATED AT 250 WORDS)