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Volume 6, Issue 11, pp. 494 - 526, November 2019

Issue cover
Cover: Low-temperature electron micrograph of a cluster of E. coli bacteria, magnified 10,000 times; each individual bacterium is oblong shaped (image by Eric Erbe, digital colorization by Christopher Pooley, both of the United States Department of Agriculture, Agricultural Research Service, image ID K11077-1 (USA); retrieved via Wikimedia Commons; the image was modified by MIC). The cover is published under the Creative Commons Attribution (CC BY) license. Enlarge issue cover

Research Articles

Type II-Metacaspases are involved in cell stress but not in cell death in the unicellular green alga Dunaliella tertiolecta

M. Teresa Mata, Armando Palma, Candela García-Gómez, María López-Parages, Víctor Vázquez, Iván Cheng-Sánchez, Francisco Sarabia, Félix López-Figueroa, Carlos Jiménez and María Segovia

page 494-508 | 10.15698/mic2019.11.696 | Full text | PDF | Abstract

Ultraviolet radiation (UVR; 280–400 nm) has a great impact on aquatic ecosystems by affecting ecophysiological and biogeochemical processes as a consequence of the global change scenario generated by anthropogenic activities. We studied the effect of PAR (P)+UVA (A)+UVB (B) i.e. PAB, on the molecular physiology of the unicellular green alga Dunaliella tertiolecta for six days. We assessed the relationship between the triggered UVR stress response and metacaspases and caspase-like (CL)activities, which are proteases denoted to participate in cell death (CD) in phytoplankton. UVR inhibited cell growth and in vivo chlorophyll a fluorescence but did not cause cell death. Western blot analyses reflected that Type-II metacaspases (MCs) are present and appear to be involved in UVR induced-cell stress but not in dark-induced CD in D. tertiolecta. Enzyme kinetics revealed that cleavage of the MCs-reporter substrates RVRR, QRR, GRR, LKR, HEK, and VLK was 10-fold higher than WEHD, DEVD, IETD, and LETD CLs-substrates. The lowest apparent Michaelis-Menten constants (KMap) corresponded to RVRRase (37.5 µM) indicating a high affinity by the RVRR substrate. The inhibition of enzymatic activities by using inhibitors with different target sites for hydrolyses demonstrated that from all of the R/ Kase activities only RVRRase was a potential candidate for being a metacaspase. In parallel, zymograms and peptide-mass fingerprinting analyses revealed the identities of such Rase activities suggesting an indirect evidence of possible natural physiological substrates of MCs. We present evidence of type II-MCs not being involved in CD in D. tertiolecta, but rather in survival strategies under the stressful irradiance conditions applied in this study.

Transcriptomic and chemogenomic analyses unveil the essential role of Com2-regulon in response and tolerance of Saccharomyces cerevisiae to stress induced by sulfur dioxide

Patrícia Lage, Belém Sampaio-Marques, Paula Ludovico, Nuno P. Mira and Ana Mendes-Ferreira

page 509-523 | 10.15698/mic2019.11.697 | Full text | PDF | Abstract

During vinification Saccharomyces cerevisiae cells are frequently exposed to high concentrations of sulfur dioxide (SO2) that is used to avoid overgrowth of unwanted bacteria or fungi present in the must. Up to now the characterization of the molecular mechanisms by which S. cerevisiae responds and tolerates SO2 was focused on the role of the sulfite efflux pump Ssu1 and investigation on the involvement of other players has been scarce, especially at a genome-wide level. In this work, we uncovered the essential role of the poorly characterized transcription factor Com2 in tolerance and response of S. cerevisiae to stress induced by SO2 at the enologically relevant pH of 3.5. Transcriptomic analysis revealed that Com2 controls, directly or indirectly, the expression of more than 80% of the genes activated by SO2, a percentage much higher than the one that could be attributed to any other stress-responsive transcription factor. Large-scale phenotyping of the yeast haploid mutant collection led to the identification of 50 Com2-targets contributing to the protection against SO2 including all the genes that compose the sulfate reduction pathway (MET3, MET14, MET16, MET5, MET10) and the majority of the genes required for biosynthesis of lysine (LYS2, LYS21, LYS20, LYS14, LYS4, LYS5, LYS1 and LYS9) or arginine (ARG5,6, ARG4, ARG2, ARG3, ARG7, ARG8, ORT1 and CPA1). Other uncovered determinants of resistance to SO2 (not under the control of Com2) included genes required for function and assembly of the vacuolar proton pump and enzymes of the antioxidant defense, consistent with the observed cytosolic and mitochondrial accumulation of reactive oxygen species in SO2-stressed yeast cells.

Microreviews

Yet another job for the bacterial ribosome

Andrea Origi, Ana Natriashivili, Lara Knüpffer, Clara Fehrenbach, Kärt Denks, Rosella Asti and Hans-Georg Koch

page 524-526 | 10.15698/mic2019.11.698 | Full text | PDF | Abstract

The ribosome is a sophisticated cellular machine, composed of RNA and protein, which translates the mRNA-encoded genetic information into protein and thus acts at the center of gene expression. Still, the ribosome not only decodes the genetic information, it also coordinates many ribosome-associated processes like protein folding and targeting. The ribosomal protein uL23 is crucial for this coordination and is located at the ribosomal tunnel exit where it serves as binding platform for targeting factors, chaperones and modifying enzymes. This includes the signal recognition particle (SRP), which facilitates co-translational protein targeting in pro- and eukaryotes, the chaperone Trigger Factor and methionine aminopeptidase, which removes the start methionine in many bacterial proteins. A recent report revealed the intricate interaction of uL23 with yet another essential player in bacteria, the ATPase SecA, which is best known for its role during post-translational secretion of proteins across the bacterial SecYEG translocon.

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