Oxygen is a major determinant of both survival and mortality of aerobic organisms. For the facultative anaerobe Lactococcus lactis, oxygen has negative effects on both growth and survival. We show here that oxygen can be beneficial to L. lactis if heme is present during aerated growth. The growth period is extended and long-term survival is markedly improved compared to results obtained under the usual fermentation conditions. We considered that improved growth and survival could be due to the capacity of L. lactis to undergo respiration. To test this idea, we confirmed that the metabolic behavior of lactococci in the presence of oxygen and hemin is consistent with respiration and is most pronounced late in growth. We then used a genetic approach to show the following. (i) The cydA gene, encoding cytochrome d oxidase, is required for respiration and plays a direct role in oxygen utilization. cydA expression is induced late in growth under respiration conditions. (ii) The hemZ gene, encoding ferrochelatase, which converts protoporphyrin IX to heme, is needed for respiration if the precursor, rather than the final heme product, is present in the medium. Surprisingly, survival improved by respiration is observed in a superoxide dismutase-deficient strain, a result which emphasizes the physiological differences between fermenting and respiring lactococci. These studies confirm respiratory metabolism in L. lactis and suggest that this organism may be better adapted to respiration than to traditional fermentative metabolism.The toxic cellular effects of oxygen are a major factor in aging and mortality (3, 28). Oxygen toxicity is attributed to the activity of reactive oxygen species that attack proteins, lipids, and nucleic acids (15). Effects of oxygen have been extensively studied by use of bacterial models, principally with the facultatively respiring bacterium Escherichia coli (see references 7 and 13 for reviews). In this model, respiration itself is implicated as a source of oxidative damage in E. coli (8, 9, 18, 20, 27, and 36). It has been suggested that the shutdown of respiration in nutrient-limited conditions may reduce reactive oxygen species levels and thereby improve E. coli survival. Recent evidence further suggests that survival is favored by shifting cells to anaerobic conditions during entry into stationary phase (9).Current information on the effects of oxygen is mainly based on respiring organisms. As such, the question of what anaerobes do in the presence of oxidative stress has been explored little. It is presumed that these organisms cope with stress in much the same way as aerobes, except that their defense systems, which may include superoxide dismutases (SODs) and catalases, may be more limited. However, there has been no demonstration to date that responses of anaerobes to an oxidative environment are predictable from the behavior of respiring bacteria.The effects of oxygen have been examined with Lactococcus lactis, a gram-positive facultative anaerobe with a fermentative metabolism that ca...

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The three space fillers allowed bone formation to occur. Nevertheless, augmented volumes declined in the Clot and Auto groups, while they remained stable with BHA. A slowly resorbable biomaterial might be suitable in sub-sinusal bone augmentation for preventing the re-expansion process and for augmenting the density of the regenerated tissues.