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Mitochondria play a pivotal role in apoptosis in multicellular organisms by releasing apoptogenic factors such as cytochrome c that activate the caspases effector pathway, and apoptosis-inducing factor (AIF) that is involved in a caspase-independent cell death pathway. Here we report that cell death in the single-celled organism Dictyostelium discoideum involves early disruption of mitochondrial transmembrane potential (⌬⌿m) that precedes the induction of several apoptosis-like features, including exposure of the phosphatidyl residues at the external surface of the plasma membrane, an intense vacuolization, a fragmentation of DNA into large fragments, an autophagy, and the release of apoptotic corpses that are engulfed by neighboring cells. We have cloned a Dictyostelium homolog of mammalian AIF that is localized into mitochondria and is translocated from the mitochondria to the cytoplasm and the nucleus after the onset of cell death. Cytoplasmic extracts from dying Dictyostelium cells trigger the breakdown of isolated mammalian and Dictyostelium nuclei in a cell-free system, and this process is inhibited by a polyclonal antibody specific for Dictyostelium discoideum apoptosis-inducing factor (DdAIF), suggesting that DdAIF is involved in DNA degradation during Dictyostelium cell death. Our findings indicate that the cell death pathway in Dictyostelium involves mitochondria and an AIF homolog, suggesting the evolutionary conservation of at least part of the cell death pathway in unicellular and multicellular organisms. INTRODUCTIONProgrammed cell death (PCD) is a genetically regulated physiological process of cell suicide that is central to the development and homeostasis of multicellular organisms (Raff, 1992;Steller, 1995;Jacobson et al., 1997;Vaux and Korsmeyer, 1999). The basic machinery that controls the onset of PCD in roundworms (Caenorhabditis elegans), insects (Drosophila melanogaster), and vertebrates (mammals) appears to be present in all cells, at all times. Crucial aspects of PCD appear to be conserved, including both the genes encoding the basic cell death machinery, and the morphological and biochemical features of apoptosis, the most frequent phenotype of PCD (Jacobson et al., 1997;Horvitz, 1999;Song and Steller, 1999;Vaux and Korsmeyer, 1999).Mitochondria play a pivotal role in PCD in mammalian cells, in particular through the permeabilization/disruption of their outer membrane, with (or followed by) the loss of mitochondrial transmembrane potential (⌬⌿m) (Kroemer et al., 1995;Green and Reed, 1998;Petit et al., 1998;Goldstein et al., 2000;Martinou et al., 2000), leading to the release of cytochrome c (Liu et al., 1996) and apoptosis-inducing factor # Corresponding author. E-mail address: pxpetit@zeus.cochin.inserm.fr. Abbreviations used: AIF, apoptosis-inducing factor; BSA, bovine serum albumin; DIF-1, differentiation-inducing factor-1; PCR, polymerase chain reaction; ⌬⌿m, mitochondrial transmembrane potential; PCD, programmed cell death; PPIX, protoporphyrin IX; PBS, phosphate-buffered saline. ©...

Campylobacter jejuni is a pathogenic, microaerophilic, gram-negative, mesophilic bacterium. Three strains isolated from humans with enteric campylobacteriosis were able to survive at high population levels (107 cells ml−1) as viable-but-nonculturable (VBNC) forms in microcosm water. The VBNC forms of the three C. jejuni strains were enumerated and characterized by using 5-cyano-2,3-ditolyl tetrazolium chloride–4′,6-diamino-2-phenylindole staining. Cellular volume, adenylate energy charge, internal pH, intracellular potassium concentration, and membrane potential values were determined in stationary-phase cell suspensions after 48 h of culture on Columbia agar and after 1 to 30 days of incubation in microcosm water and compared. A notable increase in cell volume was observed with the VBNC state; the average cell volumes were 1.73 μl mg of protein−1 for the culturable form and 10.96 μl mg of protein−1 after 30 days of incubation in microcosm water. Both the internal potassium content and the membrane potential were significantly lower in the VBNC state than in the culturable state. Culturable cells were able to maintain a difference of 0.6 to 0.9 pH unit between the internal and external pH values; with VBNC cells this difference decreased progressively with time of incubation in microcosm water. Measurements of the cellular adenylate nucleotide concentrations revealed that the cells had a low adenylate energy charge (0.66 to 0.26) after 1 day of incubation in microcosm water, and AMP was the only nucleotide detected in the three strains after 30 days of incubation in microcosm water.

Lactic beverages (LB) are products prepared with yogurt, whey, and other ingredients; they are popular among consumers in Brazil. LB containing probiotics were manufactured to study bacteria viability and to evaluate product characteristics during shelf life. Although counts decreased, 5.3 x 10 6 CFU/mL of probiotics in average after 28 d were found. LB behaved as pseudoplastic fluids with thixotropy, and flow curves were best fitted by Oswald-de-Waele model. Apparent viscosity and pH decreased slightly with storage. LB showed phase separation increasing until 35% after 14 d, stabilizing after. Finally, microscopy observations showed a dispersion of protein particles. Filamentous and spherical structures corresponded to guar and starch that were added as stabilizers. No differences were noticed between products containing yogurt bacteria and those with probiotics.