Phenotypic and genomic analysis of Zymomonas mobilis ZM4 mutants with enhanced ethanol tolerance.

Zymomonas mobilis ZM4 is an ethanol-producing microbe that is constitutively tolerant to this solvent. For a better understanding of the ethanol tolerance phenomenon we obtained and characterized two ZM4 mutants (ER79ap and ER79ag) with higher ethanol tolerance than the wild-type. Mutants were evaluated in different ethanol concentrations and this analysis showed that mutant ER79ap was more tolerant and had a better performance in terms of cell viability, than the wild-type strain and ER79ag mutant. Genotyping of the mutant strains showed that both carry non-synonymous mutations in clpP and spoT/relA genes. A third non-synonymous mutation was found only in strain ER79ap, in the clpB gene. Considering that ER79ap has the best tolerance to added ethanol, the mutant alleles of this strain were evaluated in ZM4 and here we show that while all of them contribute to ethanol tolerance, mutation within spoT/relA gene seems to be the most important.

Genomic lineages of Rhizobium etli revealed by the extent of nucleotide polymorphisms and low recombination.

BACKGROUND: Most of the DNA variations found in bacterial species are in the form of single nucleotide polymorphisms (SNPs), but there is some debate regarding how much of this variation comes from mutation versus recombination. The nitrogen-fixing symbiotic bacteria Rhizobium etli is highly variable in both genomic structure and gene content. However, no previous report has provided a detailed genomic analysis of this variation at nucleotide level or the role of recombination in generating diversity in this bacterium. Here, we compared draft genomic sequences versus complete genomic sequences to obtain reliable measures of genetic diversity and then estimated the role of recombination in the generation of genomic diversity among Rhizobium etli. RESULTS: We identified high levels of DNA polymorphism in R. etli, and found that there was an average divergence of 4% to 6% among the tested strain pairs. DNA recombination events were estimated to affect 3% to 10% of the genomic sample analyzed. In most instances, the nucleotide diversity (π) was greater in DNA segments with recombinant events than in non-recombinant segments. However, this degree of recombination was not sufficiently large to disrupt the congruence of the phylogenetic trees, and further evaluation of recombination in strains quartets indicated that the recombination levels in this species are proportionally low. CONCLUSION: Our data suggest that R. etli is a species composed of separated lineages with low homologous recombination among the strains. Horizontal gene transfer, particularly via the symbiotic plasmid characteristic of this species, seems to play an important role in diversity but the lineages maintain their evolutionary cohesiveness.

Comportamiento de la mortalidad perinatal en gestantes con avanzada edad materna (2005-2009) / Behavior of perinatal mortality in pregnant women with advanced maternal age (2005-2009)

El embarazo en los extremos de la vida reproductiva ha sido siempre una preocupación para quienes tienen la tarea de atender a las futuras madres. Se realizó un estudio transversal, descriptivo, retrospectivo, en el Hospital Universitario Gineco-Obstétrico Mariana Grajales de Villa Clara, entre el 1 ro de enero de 2005 y el 31 de diciembre de 2009, para caracterizar el comportamiento de la mortalidad perinatal en gestantes con avanzada edad materna. Se tomó una muestra no probabilística intencional constituida por las muertes perinatales ocurridas en gestantes con edad igual o mayor a 35 años en el momento del parto. Además, se consideró como referencia una muestra no probabilística intencional de todas las muertes perinatales ocurridas en gestantes entre 20-34 años. Se tuvieron en cuenta las siguientes variables: mortalidad perinatal, edad materna, sexo del producto de la concepción, edad gestacional al parto, peso del recién nacido, lugar de la defunción, ocurrencia de la defunción, causa de muerte. Se comprobó que los nacimientos en gestantes de 35 años y más representaron el 13,1 por ciento del total de nacimientos, con una tasa de mortalidad perinatal elevada que osciló entre 18,4 y 28,6 por mil nacidos vivos. Predominó la mortalidad fetal, el sexo masculino, el bajo peso y la prematuridad, con una ocurrencia intrahospitalaria intraparto, y como causa de muerte fetal, el 32,0 por ciento correspondió a enfermedades placentarias. Se recomienda prestar mayor atención al riesgo preconcepcional y profundizar en el análisis de cada defunción fetal para identificar un mayor número de causas(AU)

Conserved symbiotic plasmid DNA sequences in the multireplicon pangenomic structure of Rhizobium etli.

Strains of the same bacterial species often show considerable genomic variation. To examine the extent of such variation in Rhizobium etli, the complete genome sequence of R. etli CIAT652 and the partial genomic sequences of six additional R. etli strains having different geographical origins were determined. The sequences were compared with each other and with the previously reported genome sequence of R. etli CFN42. DNA sequences common to all strains constituted the greater part of these genomes and were localized in both the chromosome and large plasmids. About 700 to 1,000 kb of DNA that did not match sequences of the complete genomes of strains CIAT652 and CFN42 was unique to each R. etli strain. These sequences were distributed throughout the chromosome as individual genes or chromosomal islands and in plasmids, and they encoded accessory functions, such as transport of sugars and amino acids, or secondary metabolism; they also included mobile elements and hypothetical genes. Sequences corresponding to symbiotic plasmids showed high levels of nucleotide identity (about 98 to 99%), whereas chromosomal sequences and the sequences with matches to other plasmids showed lower levels of identity (on average, about 90 to 95%). We concluded that R. etli has a pangenomic structure with a core genome composed of both chromosomal and plasmid sequences, including a highly conserved symbiotic plasmid, despite the overall genomic divergence.

A common genomic framework for a diverse assembly of plasmids in the symbiotic nitrogen fixing bacteria.

This work centres on the genomic comparisons of two closely-related nitrogen-fixing symbiotic bacteria, Rhizobium leguminosarum biovar viciae 3841 and Rhizobium etli CFN42. These strains maintain a stable genomic core that is also common to other rhizobia species plus a very variable and significant accessory component. The chromosomes are highly syntenic, whereas plasmids are related by fewer syntenic blocks and have mosaic structures. The pairs of plasmids p42f-pRL12, p42e-pRL11 and p42b-pRL9 as well large parts of p42c with pRL10 are shown to be similar, whereas the symbiotic plasmids (p42d and pRL10) are structurally unrelated and seem to follow distinct evolutionary paths. Even though purifying selection is acting on the whole genome, the accessory component is evolving more rapidly. This component is constituted largely for proteins for transport of diverse metabolites and elements of external origin. The present analysis allows us to conclude that a heterogeneous and quickly diversifying group of plasmids co-exists in a common genomic framework.