Analysis of 16S rRNA gene mutations in a subset of Aeromonas strains and their impact in species delineation

Characterization of 999 Aeromonas strains using a published 16S rDNA RFLP identification method showed that 8.1% of the strains produced unexpected (hereafter called «atypical») restriction patterns, making their identification uncertain. Atypical patterns were due to the presence of nucleotide polymorphisms among the rrn operons of the 16S rRNA gene (so-called microheterogeneities). Double sequencing signals at certain positions revealed the nucleotide composition was responsible for the microheterogeneities. Although the number of microheterogeneities was relatively low (0.06-0.66%), trees inferred from the 16S rRNA gene led either to a misidentification or to an inconclusive result for the majority of these strains. Strains with atypical patterns were, however, correctly identified using the rpoD gene sequences, as belonging to Aeromonas caviae, A. veronii, and A. media. All of them, but particularly the two former species, are associated with human disease. Microheterogeneities in 16S rRNA gene sequence were significantly (P 0.01) more prevalent in clinical than in environmental strains. This work also analyzed the effects of these microheterogeneities on the taxonomic position of the investigated strains. The results suggest the need for recording microheterogeneities in the 16S rRNA gene (AU)

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Evidence of an association between poly(3-hydroxybutyrate) accumulation and phosphotransbutyrylase expression in Bacillus megaterium / Evidencia de la asociación entre la acumulación de poly(3-hidroxibutirato) y la expresión de fosfotransbutirilasa en Bacillus megaterium

Molecular analysis of a genomic region of Bacillus megaterium, a polyhydroxybutyrate (PHB)-producing microorganism, revealed the presence of a gene coding for the enzyme phosphotransbutyrylase (Ptb). Enzyme activity was measured throughout the different growth phases of B. megaterium and was found to correlate with PHB accumulation during the late-exponential growth phase. Ptb expression was repressed by glucose and activated by the branched amino acids isoleucine and valine. Overexpression of Act(Bm), a sigma(54) regulator from B. megaterium whose gene is located upstream from ptb, caused an increase in Ptb activity and PHB accumulation in B. megaterium (AU)

El análisis molecular de una región del genoma de Bacillus megaterium, un microorganismo productor de polihidroxibutirato (PHB), reveló la presencia de un gen que codifica la enzima fosfotransbutirilasa (Ptb). La actividad enzimática se midió durante las diferentes fases de crecimiento de B. megaterium y se vio que su actividad estaba asociada a la acumulación de PHB al final de la fase de crecimiento exponencial. La glucosa inhibía la expresión de Ptb, mientras que los aminoácidos ramificados isoleucina y valina la activaban. La sobreexpresión de ActBm, un regulador sigma 54 de B. megaterium cuyo gen se encuentra en dirección 5’ a partir del gen ptb, hacía aumentar la actividad de Ptb y la acumulación de PHB en B. megaterium (AU)