Relatively stable physical conditions in caves allow for the examination of the relationship between geochemical processes and the activity of microorganisms, reflected in substantial rock alterations, formation of new structures, surface deterioration and cave expansion. Although caves are considered as extreme environments, they are inhabited by microbial communities with unexpected diversity. While Proteobacteria and Actinobacteria are the most ubiquitous groups, also the presence of Archaea has been frequently noted recently. Here, we present a summary of results on diversity of cave microorganisms in the context of taxon distribution as well as the contribution and role of individual taxa in cave ecosystems.

PSM19035 of the pathogenic bacterium Streptococcus pyogenes is a low-copy-number plasmid carrying erythromycin resistance, stably maintained in a broad range of gram-positive bacteria. We show here that the ω -ε-ζ operon of this plasmid constitutes a novel proteic plasmid addiction system in which the ε and ζ genes encode an antitoxin and toxin, respectively, while ω plays an autoregulatory function. Expression of toxin Zeta is bactericidal for the gram-positive Bacillus subtilis and bacteriostatic for the gram-negative Escherichia coli . The toxic effects of ζ gene expression in both bacterial species are counteracted by proper expression of ε. The ε -ζ toxin-antitoxin cassette stabilizes plasmids in E. coli less efficiently than in B. subtilis .

Breast milk is a natural food and important component of infant nutrition. Apart from the alimentary substances, breast milk contains many important bioactive compounds, including endogenous microRNA molecules (miRNAs). These regulatory molecules were identified in various mammalian biological fluids and were shown to be mostly packed in exosomes. Recently, it was revealed that plant food-derived miRNAs are stably present in human blood and regulate the expression of specific human genes. Since then, the scientific community has focused its efforts on contradicting or confirming this discovery. With the same intention, qRT-PCR experiments were performed to evaluate the presence of five plant food-derived miRNAs (miR166a, miR156a, miR157a, miR172a and miR168a) in breast milk (whole milk and exosomes) from healthy volunteers. In whole milk samples, all examined miRNAs were identified, while only two of these miRNAs were confirmed to be present in exosomes. The plant miRNA concentration in the samples ranged from 4 to 700 fM. Complementary bioinformatics analysis suggests that the evaluated plant miRNAs may potentially influence several crucial biological pathways in the infant organism.

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.

Emerging important Acinetobacter strains commonly accommodate a plethora of mobile elements including plasmids of different size. Plasmids, apart from encoding modules enabling their self-replication and/or transmission, can carry a diverse number of genes, allowing the host cell to survive in an environment that would otherwise be lethal or restrictive for growth. The present study characterizes the plasmidome generated from an arsenic-resistant strain named ZS207, classified as Acinetobacter lwoffii. Sequencing effort revealed the presence of nine plasmids in the size between 4.3 and 38.4 kb as well as one 186.6 kb megaplasmid. All plasmids, except the megaplasmid, do apparently not confer distinguishing phenotypic features. In contrast, the megaplasmid carries arsenic and heavy metals resistance regions similar to those found in permafrost A. lwoffii strains. In-depth in silico analyses have shown a significant similarity between the regions from these plasmids, especially concerning multiple transposable elements, transfer and mobilization genes, and toxin-antitoxin systems. Since ars genes encode proteins of major significance in terms of potential use in bioremediation, arsenic resistance level of ZS207 was determined and the functionality of selected ars genes was examined. Additionally, we checked the functionality of plasmid-encoded toxin-antitoxin systems and their impact on the formation of persister cells.