Gudrun Wolf

Heme-dependent and heme-independent nitrite reduction by lactic acid bacteria results in different N-containing products

Seventy strains of lactic acid bacteria were investigated for nitrite reductase activity. Two types of this activity were detected. Type I was found in Lactobacillus plantarum, L. pentosus and Pediococcus pentosaceus. This activity is heme-dependent with ammonia as the sole product. Type II mechanism is heme-independent and reduces nitrite to NO and N2O.

Heme-dependent catalase activity of lactobacilli

The heme-dependent catalase in Lactobacillus pentosus, L. sake, L. delbrueckii and Enterococcus faecalis was studied. The catalase was formed by cells grown aerobically in the presence of hematin or for lactobacilli when grown without added hematin, after incubation of buffered cells in the presence of hematin. The kinetics of the production of catalase revealed maximum activity for L. pentosus and E. faecalis at late stationary and late logarithmic growth phase, respectively. The physiological role of catalase was studied with L. sake. The presence of hematin allows higher growth yields, since it protects the cells against hydrogen peroxide formed endogenously up to concentrations of 4.6 mmol/l.

Production of formate, acetate, and succinate by anaerobic fermentation of Lactobacillus pentosus in the presence of citrate

SummaryThe formation of acetate, formate and succinate was studied in Lactobacillus pentosus. These compounds were produced in addition to lactic acid when cells were exposed to anaerobic growth conditions with limited carbohydrates and in the presence of citrate. Citrate was metabolised via oxalacetate serving as an H-acceptor in a joint process together with lactate. The metabolism of citrate resulted in stoichiometric amounts of succinate and acetate. Lactate was degraded to formate and acetate in a reaction catalysed by pyruvate formate lyase. These fermentation products can potentially affect the flavour of fermented food but ecological factors in fermenting meat, e.g. the presence of glucose, nitrate or nitrite prevent this reaction.

Physiological diversity among strains of Tetragenococcus halophilus

Summary Twenty one strains of Tetragenococcus halophilus were investigated for their ecological properties, e.g. growth rate, salt tolerance, pH-dependence and influence of oxygen. All strains tolerated 26% NaCl. The growth rate was optimum at pH 7.5. Anaerobically grown cultures of the type strain achieved a higher growth rate than aerobic cultures. The addition of hematin to aerobic cultures resulted in a reduction in the lag phase and in generation time and a twofold increase in growth yield. Under these growth conditions 12 strains exhibited catalase activity. The composition of the metabolic end products was strongly affected by the growth conditions. Anaerobically grown cultures produced lactate, acetate and formate, whereas acetate was the main product of aerobic cultures.

Heme-Dependent Cytochrome Formation in Lactobacillus maltaromicus

Summary Functional cytochromes of the b and d types were detected in crude extracts of Lactobacillus maltaromicus grown aerobically in the presence of hematin. With the addition of hematin to the medium the growth yield under aerobic growth conditions was tenfold higher than observed with anaerobically grown cultures. In addition, an increase was observed of acetoin formation. Our results are consistent with the phylogenetic and metabolic relationship between enterococci and carnobacteria including L. maltaromicus as a species to be transferred to the genus Carnobacterium .

Reduction of Nitrite by Staphylococcus carnosus and Staphylococcus piscifermen tans

Summary Strains of Staphylococcus carnosus and Staphylococcus pisciferatentans are employed in food fermentations. The organisms arc expected to perform among other desired reactions an effective reduction of nitrate and nitrite. We have investigated the potential to perform these reactions with resting cells of S. carnosus (16 strains) and S. piscifermentans (10 strains). It was observed that all strains reduced nitrite and three strains that were investigated in more detail formed ammonia as the only metabolic end product. The reduction of nitrite was inhibited in the presence of nitrate, whereas neither amino acids nor ammonia exhibited an effect on the reaction. Nitrite and nitrate are used as terminal electron acceptors and support growth under anaerobic conditions as evidenced by the increase in growth yield. These data are consistent with a dissimilatory type of nitrite reduction.