Natural Genetic Transformation Generates a Population of Merodiploids in Streptococcus pneumoniae.

Contains fulltext : 119152.pdf (publisher's version ) (Open Access)Partial duplication of genetic material is prevalent in eukaryotes and provides potential for evolution of new traits. Prokaryotes, which are generally haploid in nature, can evolve new genes by partial chromosome duplication, known as merodiploidy. Little is known about merodiploid formation during genetic exchange processes, although merodiploids have been serendipitously observed in early studies of bacterial transformation. Natural bacterial transformation involves internalization of exogenous donor DNA and its subsequent integration into the recipient genome by homology. It contributes to the remarkable plasticity of the human pathogen Streptococcus pneumoniae through intra and interspecies genetic exchange. We report that lethal cassette transformation produced merodiploids possessing both intact and cassette-inactivated copies of the essential target gene, bordered by repeats (R) corresponding to incomplete copies of IS861. We show that merodiploidy is transiently stimulated by transformation, and only requires uptake of a approximately 3-kb DNA fragment partly repeated in the chromosome. We propose and validate a model for merodiploid formation, providing evidence that tandem-duplication (TD) formation involves unequal crossing-over resulting from alternative pairing and interchromatid integration of R. This unequal crossing-over produces a chromosome dimer, resolution of which generates a chromosome with the TD and an abortive chromosome lacking the duplicated region. We document occurrence of TDs ranging from approximately 100 to approximately 900 kb in size at various chromosomal locations, including by self-transformation (transformation with recipient chromosomal DNA). We show that self-transformation produces a population containing many different merodiploid cells. Merodiploidy provides opportunities for evolution of new genetic traits via alteration of duplicated genes, unrestricted by functional selective pressure. Transient stimulation of a varied population of merodiploids by transformation, which can be triggered by stresses such as antibiotic treatment in S. pneumoniae, reinforces the plasticity potential of this bacterium and transformable species generally

Aspergilose invasiva do seio esfenoidal e paralisia do sexto nervo

A aspergilose do seio esfenoidal é doença rara e pode se apresentar sob diferentes formas clínicas devido a envolvimento de. diversas estruturas anatomicamente adjacentes ao seio esfenoidal. Relatamos o caso de uma paciente com 74 anos de idade, diabética, com paralisia do sexto nervo esquerdo secundária a aspergilose do seio esfenoidal. Não havia história de cefaléia ou de queixas sugestivas de alergia respiratória. A tomografia computadorizada revelou lesão etmoídeo-esfenoidal à esquerda, com presença de imagem cálcica em seu interior e destruição óssea. A paciente foi submetida a cirurgia com retirada de material necrótico e debridamento da lesão, seguida de tratamento com anfote-ricina B e 5-fluorocitosina. Exame histológico revelou a presença de hifas sugestivas de Aspergilius sp. Após três meses de tratamento a paciente apresentou recuperação total da paresia do nervo abducente. O diagnóstico clínico pré-operatório de aspergilose do seio esfenoidal é difícil. No entanto, a presença de imagem cálcica ou de densidade metálica à radiografia simples de crânio ou à tomografia computadorizada sugere fortemente o diagnóstico. O exame hihstológico revela a presença de hifas dicotomatosas em 45,0 típicas do Aspergilius. O tratamento inclui excisão e debridamento da lesão seguida do uso de anfo-tericina B associada a 5-fluorocitosina ou rifampicina