T6SS intraspecific competition orchestrates Vibrio cholerae genotypic diversity

Vibrio cholerae is a diverse species that inhabits a wide range of environments from copepods in brackish water to the intestines of humans. In order to remain competitive, V. cholerae uses the versatile type-VI secretion system (T6SS) to secrete anti-prokaryotic and anti-eukaryotic effectors. In addition to competing with other bacterial species, V. cholerae strains also compete with one another. Some strains are able to coexist, and are referred to as belonging to the same compatibility group. Challenged by diverse competitors in various environments, different V. choleare strains secrete different combination of effectors - presumably to best suit their niche. Interestingly, all pandemic V. cholerae strains encode the same three effectors. In addition to the diversity displayed in the encoded effectors, the regulation of V. cholerae also differs between strains. Two main layers of regulation appear to exist. One strategy connects T6SS activity with behavior that is suited to fighting eukaryotic cells, while the other is linked with natural competence - the ability of the bacterium to acquire and incorporate extracellular DNA. This relationship between bacterial killing and natural competence is potentially a source of diversification for V. cholerae as it has been shown to incorporate the DNA of cells recently killed through T6SS activity. It is through this process that we hypothesize the transfer of virulence factors, including T6SS effector modules, to happen. Switching of T6SS effectors has the potential to change the range of competitors V. cholerae can kill and to newly define which strains V. cholerae can co-exist with, two important parameters for survival in diverse environments (AU)

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Genomic Plasticity of Vibrio cholerae

Vibrio cholerae is one of the deadliest pathogens in the history of humankind. It is the causative agent of cholera, a disease characterized by a profuse and watery diarrhoea that still today causes 95.000 deaths worldwide every year. V. cholerae is a free living marine organism that interacts with and infects a variety of organisms, from amoeba to humans, including insects and crustaceans. The complexity of the lifestyle and ecology of V. cholerae suggests a high genetic and phenotypic plasticity. In this review, we will focus on two peculiar genomic features that enhance genetic plasticity in this bacterium: the division of its genome in two different chromosomes and the presence of the superintegron, a gene capture device that acts as a large, low-cost memory of adaptive functions, allowing V. cholerae to adapt rapidly (AU)

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Bacteroides mobilizable and conjugative genetic elements: antibiotic resistance among clinical isolates

La conjugación es uno de los mecanismos más importantes de la transferencia horizontal de genes en procariotas, lo que lleva a la variación genética dentro de una especie y la adquisición de nuevos rasgos, como la resistencia a los antibióticos. Bacteroides es un anaerobio obligado y un patógeno oportunista importante. La resistencia a los antibióticos entre especies de Bacteroides está aumentando rápidamente, debido en gran parte a la difusión de los factores de transferencia de ADN (plásmidos y transposones) albergado por los miembros de este género. Los factores de transferencia se pueden dividir en dos clases, conjugativos y movilizables. Las especies de Bacteroides han presentado plásmidos de resistencia a los antibióticos, todos los cuales han sido intensamente estudiados. Estos plásmidos codifican de alto nivel de resistencia MLS conferida por un gen erm conservado. Se ha informado una observación interesante asociada a la transferencia de varios de estos tipos de elementos, todo lo cual confiere mayor resistencia y que aparecen en gran medida la eficiencia de transferencia después de la exposición a la tetraciclina. Muchos de los transposones conjugativos (CTn) en Bacteroides están relacionados con varios elementos genéticos (como CTnDOT, CnTnERL, NBU y otros). CTnDOT lleva un gen de resistencia a la tetraciclina, tetQ, y un gen de resistencia a la eritromicina, ermF. La resistencia a los medicamentos utilizados para tratar infecciones por Bacteroides, tales como la clindamicina, también ha ido en aumento. Estos elementos conjugativos han sido encontrados en los aislados clínicos de Bacteroides. Por lo tanto, la transferencia horizontal de genes posiblemente podría jugar un papel importante en la creciente incidencia de la resistencia bacteriana en este grupo(AU)

The conjugation is one of the most important mechanisms of horizontal gene transfer in prokaryotes, leading to genetic variation within a species and the acquisition of new traits, such as antibiotic resistance. Bacteroides is an obligate anaerobe of the colon and a significant opportunistic pathogen. Antibiotic resistance among Bacteroides spp. is rapidly increasing, largely due to the dissemination of DNA transfer factors (plasmids and transposons) harbored by members of this genus. Transfer factors can be divided into two classes, conjugative and mobilizable. Species of the intestinal Bacteroides have yielded different resistance plasmids, all of which have been intensely studied, the plasmids encode high-level MLS resistance conferred by a conserved erm gene. It has been reported an interesting observation associated with the transfer of several of these types of elements, all of which conferred Tcr and displayed greatly increased transfer efficiency following exposure to tetracycline. Many of the conjugative transposons (CTns) in Bacteroides are related to various genetic elements (such as CTnDOT, CTnERL, NBU and others). CTnDOT carries a tetracycline resistance gene, tetQ, and an erythromycin resistance gene, ermF. Resistance to drugs used to treat Bacteroides infections, such as clindamycin, has also been increasing. These conjugal elements have been found in Bacteroides clinical isolates. Thus, horizontal gene transfer could conceivably have played a role in the rising incidence of resistance in this bacterial group(AU)

Prokaryotic community structure in algal photosynthetic biofilms from extreme acidic streams in Río Tinto (Huelva, Spain)

Four algal photosynthetic biofilms were collected from the Río Tinto (SW Spain) at four localities: AG, Euglena and Pinnularia biofilms; ANG, Chlorella and Pinnularia biofilms; RI, Cyanidium and Dunaliella biofilms; and CEM, Cyanidium, Euglena and Pinnularia biofilms. Community composition and structure were studied by a polyphasic approach consisting of 16S rRNA analysis, scanning electron microscopy by back-scattered electron detection mode (SEM-BSE), and fluorescence in-situ hybridization (FISH). Acidophilic prokaryotes associated with algal photosynthetic biofilms included sequences related to the Alpha-, Beta-, and Gammaproteobacteria (phylum Proteobacteria) and to the phyla Nitrospira, Actinobacteria, Acidobacteria and Firmicutes. Sequences from the Archaea domain were also identified. No more than seven distinct lineages were detected in any biofilm, except for those from RI, which contained fewer groups of Bacteria. Prokaryotic communities of the thinnest algal photosynthetic biofilms (-100 microm) were more related to those in the water column, including Leptospirillum populations. In general, thick biofilms (200 microm) generate microniches that could facilitate the development of less-adapted microorganisms (coming from the surrounding environment) to extreme conditions, thus resulting in a more diverse prokaryotic biofilm (AU)

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Osmoadaptation mechanisms in prokaryotes: distribution of compatible solutes

Microorganisms respond to osmotic stress mostly by accumulating compatible solutes, either by uptake from the medium or by de novo synthesis. These osmotically active molecules preserve the positive turgor pressure required for cell division. The diversity of compatible solutes is large but falls into a few major chemical categories; they are usually small organic molecules such as amino acids or their derivatives, and carbohydrates or their derivatives. Some are widely distributed in nature while others seem to be exclusively present in specific groups of organisms. This review discusses the diversity and distribution of known classes of compatible solutes found in prokaryotes as well as the increasing knowledge of the genes and pathways involved in their synthesis. The alternative roles of some archetypal compatible solutes not subject to osmoregulatory constraints are also discussed (AU)

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