When death was young: an ancestral apoptotic network in bacteria

Lupeol-induced nitric oxide elicits apoptosis-like death within Escherichia coli in a DNA fragmentation-independent manner

Lupeol is known to be plentiful in fruits or plant barks and has an antimicrobial effect, however, its mode of action(s) has yet to be determined. To elucidate lupeol generates nitric oxide (NO), which is recognized for possessing an antimicrobial activity, intracellular NO was measured in Escherichia coli using DAF-FM. Using the properties of NO passing through plasma membrane easily, increased malondialdehyde levels have shown that lupeol causes lipid peroxidation, and the resulting membrane depolarization was confirmed by DiBAC4(3). These data indicated that lupeol-induced NO is related to the destruction of bacterial membrane. Further study was performed to examine whether NO, known as a cell proliferation inhibitor, affects bacterial cell division. As a result, DAPI staining verified that lupeol promotes cell division arrest, and followed by early apoptosis is observed in Annexin V/PI double staining. Even though these apoptotic hallmarks appeared, the endonuclease failed to perform properly with supporting data of decreased intracellular Mg2+ and Ca2+ levels without DNA fragmentation, which is confirmed using a TUNEL assay. These findings indicated that lupeol-induced NO occurs DNA fragmentation-independent bacterial apoptosis-like death (ALD). Additionally, lupeol triggers DNA filamentation and morphological changes in response to DNA repair system called SOS system. In accordance with the fact that ALD deems to SOS response, and that the RecA is considered as a caspase-like protein, increase in caspase-like protein activation occurred in E. coli wild-type, and no ΔRecA mutant. In conclusion, these results demonstrated that the antibacterial mode of action(s) of lupeol is an ALD while generating NO.

Functional identification behind gravity-separated sludge in high concentration organic coking wastewater: Microbial aggregation, apoptosis-like decay and community

Functional identification and elimination of activity-decayed sludge are helpful for improving the performance of biological treatment process. However, cell decay-associated changes in biological functions have not been explored for gravity-separated sludge. In this work, sludge flocs from the aerobic basin of a wastewater treatment plant treating high-concentration organic coking wastewater was fractionated according to settling velocity, i.e. sludge F (fast settling), sludge M (moderate settling) and sludge S (slow settling). Sludge volume index (SVI), mean floc size, dehydrogenase activity, specific oxygen uptake rate (SOUR), extracellular polymeric substances (EPS) content and aggregation interaction were investigated in the fractionated sludges. Apoptosis-like decayed cell distribution (ALDCD), a novel property of sludge, was proposed to describe sludge decay based on cell membrane variation. ALDCD of sludge F was 6.64% and 13.5% lower than sludge M and S, respectively. Microbial community and functional prediction revealed that sludge F exhibited the highest microbial potential for organic removal and sludge M had the highest potential for nitrogen metabolism while sludge S had the lowest potential for both. Our analysis suggests that the treatment efficiency might be enhanced by retaining compact sludge flocs while eliminating dispersive sludge flocs. This study also facilitates the identification and elimination of functional microbial groups from decayed sludge in wastewater treatment.

Ancestral State Reconstruction of the Apoptosis Machinery in the Common Ancestor of Eukaryotes

Apoptotic cell death is a type of eukaryotic cell death. In animals, it regulates development, is involved in cancer suppression, and causes cell death during pathological aging of neuronal cells in neurodegenerative diseases such as Alzheimer's. Mitochondrial apoptotic-like cell death, a form of primordial apoptosis, also occurs in unicellular organisms. Here, we ask the question why the apoptosis machinery has been acquired and maintained in unicellular organisms and attempt to answer it by performing ancestral state reconstruction. We found indications of an ancient evolutionary arms race between protomitochondria and host cells, leading to the establishment of the currently existing apoptotic pathways. According to this reconstruction, the ancestral protomitochondrial apoptosis machinery contained both caspases and metacaspases, four types of apoptosis induction factors (AIFs), both fungal and animal OMI/HTR proteases, and various apoptotic DNases. This leads to the prediction that in extant unicellular eukaryotes, the apoptotic factors are involved in mitochondrial respiration and their activity is needed exclusively in aerobic conditions. We test this prediction experimentally using yeast and find that a loss of the main apoptotic factors is beneficial under anaerobic conditions yet deleterious under aerobic conditions in the absence of lethal stimuli. We also point out potential medical implications of these findings.

Guidelines and recommendations on yeast cell death nomenclature

Elucidating the biology of yeast in its full complexity has major implications for science, medicine and industry. One of the most critical processes determining yeast life and physiology is cel-lular demise. However, the investigation of yeast cell death is a relatively young field, and a widely accepted set of concepts and terms is still missing. Here, we propose unified criteria for the defi-nition of accidental, regulated, and programmed forms of cell death in yeast based on a series of morphological and biochemical criteria. Specifically, we provide consensus guidelines on the differ-ential definition of terms including apoptosis, regulated necrosis, and autophagic cell death, as we refer to additional cell death rou-tines that are relevant for the biology of (at least some species of) yeast. As this area of investigation advances rapidly, changes and extensions to this set of recommendations will be implemented in the years to come. Nonetheless, we strongly encourage the au-thors, reviewers and editors of scientific articles to adopt these collective standards in order to establish an accurate framework for yeast cell death research and, ultimately, to accelerate the pro-gress of this vibrant field of research.

Mitochondrial regulation of cell death: a phylogenetically conserved control

Mitochondria are fundamental for eukaryotic cells as they participate in critical catabolic and anabolic pathways. Moreover, mitochondria play a key role in the signal transduction cascades that precipitate many (but not all) regulated variants of cellular demise. In this short review, we discuss the differential implication of mitochondria in the major forms of regulated cell death.

Characterization of cell death in Escherichia coli mediated by XseA, a large subunit of exonuclease VII

Exonuclease VII (ExoVII) of Escherichia coli is a single strandspecific DNA nuclease composed of two different subunits: the large subunit, XseA, and the small subunit, XseB. In this study, we found that multicopy single-stranded DNAs (msDNAs), Ec83 and Ec78, are the in vivo substrates of ExoVII; the enzyme cuts the phosphodiester bond between the fourth and fifth nucleotides from the 5'end. We used this msDNA cleavage to assess ExoVII activity in vivo. Both subunits were required for enzyme activity. Expression of XseA without XseB caused cell death, even though no ExoVII activity was detected. The lethality caused by XseA was rescued by surplus XseB. In XseA-induced death, cells were elongated and multinucleated, and their chromosomes were fragmented and condensed; these are the morphological hallmarks of apoptotic cell death in bacteria. A putative caspase recognition sequence (FVAD) was found in XseA, and its hypothetical caspase product with 257 amino acids was as active as the intact protein in inducing cell death. We propose that under ordinary conditions, XseA protects chromosome as a component of the ExoVII enzyme, but in some conditions, the protein causes cell death; the destruction of cell is probably carried out by the amino terminal fragment derived from the cleavage of XseA by caspase-like enzyme.

Multiparameter analysis of apoptosis in puromycin-treated Saccharomyces cerevisiae

In Saccharomyces cerevisiae, a typical apoptotic phenotype is induced by some stress factors such as sugars, acetic acid, hydrogen peroxide, aspirin and age. Nevertheless, no data have been reported for apoptosis induced by puromycin, a damaging agent known to induce apoptosis in mammalian cells. We treated S. cerevisiae with puromycin to induce apoptosis and evaluated the percentage of dead cells by using Hoechst 33342 staining, transmission electron microscopy (TEM) and Annexin V flow cytometry (FC) analysis. Hoechst 33342 fluorescence images were processed to acquire parameters to use for multiparameter analysis [and perform a principal component analysis, (PCA)]. Cell viability was evaluated by Rhodamine 123 (Rh 123) and Acridine Orange microscope fluorescence staining. The results show puromycin-induced apoptosis in S. cerevisiae, and the PCA analysis indicated that the increasing percentage of apoptotic cells delineated a well-defined graph profile. The results were supported by TEM and FC. This study gives new insights into yeast apoptosis using puromycin as inducer agent, and PCA analysis may complement molecular analysis facilitating further studies to its detection.

Apoptosis-like death, an extreme SOS response in Escherichia coli

In bacteria, SOS is a global response to DNA damage, mediated by the recA-lexA genes, resulting in cell cycle arrest, DNA repair, and mutagenesis. Previously, we reported that Escherichia coli responds to DNA damage via another recA-lexA-mediated pathway resulting in programmed cell death (PCD). We called it apoptosis-like death (ALD) because it is characterized by membrane depolarization and DNA fragmentation, which are hallmarks of eukaryotic mitochondrial apoptosis. Here, we show that ALD is an extreme SOS response that occurs only under conditions of severe DNA damage. Furthermore, we found that ALD is characterized by additional hallmarks of eukaryotic mitochondrial apoptosis, including (i) rRNA degradation by the endoribonuclease YbeY, (ii) upregulation of a unique set of genes that we called extensive-damage-induced (Edin) genes, (iii) a decrease in the activities of complexes I and II of the electron transport chain, and (iv) the formation of high levels of OH˙ through the Fenton reaction, eventually resulting in cell death. Our genetic and molecular studies on ALD provide additional insight for the evolution of mitochondria and the apoptotic pathway in eukaryotes.

The SOS response is the first described and the most studied bacterial response to DNA damage. It is mediated by a set of two genes, recA-lexA, and it results in DNA repair and thereby in the survival of the bacterial culture. We have shown that Escherichia coli responds to DNA damage by an additional recA-lexA-mediated pathway resulting in an apoptosis-like death (ALD). Apoptosis is a mode of cell death that has previously been reported only in eukaryotes. We found that E. coli ALD is characterized by several hallmarks of eukaryotic mitochondrial apoptosis. Altogether, our results revealed that recA-lexA is a DNA damage response coordinator that permits two opposite responses: life, mediated by the SOS, and death, mediated by the ALD. The choice seems to be a function of the degree of DNA damage in the cell.

The cell death protease Kex1p is essential for hypochlorite-induced apoptosis in yeast

Following microbial pathogen invasion, the human immune system of activated phagocytes generates and releases the potent oxidant hypochlorous acid (HOCl), which contributes to the killing of menacing microorganisms. Though tightly controlled, HOCl generation by the myeloperoxidase-hydrogen peroxide-chloride system of neutrophils/monocytes may occur in excess and lead to tissue damage. It is thus of marked importance to delineate the molecular pathways underlying HOCl cytotoxicity in both microbial and human cells. Here, we show that HOCl induces the generation of reactive oxygen species (ROS), apoptotic cell death and the formation of specific HOCl-modified epitopes in the budding yeast Saccharomyces cerevisiae. Interestingly, HOCl cytotoxicity can be prevented by treatment with ROS scavengers, suggesting oxidative stress to mediate the lethal effect. The executing pathway involves the pro-apoptotic protease Kex1p, since its absence diminishes HOCl-induced production of ROS, apoptosis and protein modification. By characterizing HOCl-induced cell death in yeast and identifying a corresponding central executor, these results pave the way for the use of Saccharomyces cerevisiae in HOCl research, not least given that it combines both being a microorganism as well as a model for programmed cell death in higher eukaryotes.