Comparison of culturable Gram-negative bacterial community structures in the rhizosphere of three fruit plants

This research work was oriented to outlining the diversity of Gram-negative culturable portion of the bacterial community in three fruit plants rhizosphere. Rhizosphere samples were taken from European chestnut (Castanea sativa Mill), true service tree (Sorbus domestica L.) and cornelian cherry (Cornus mas L.) plants. Experiments were conducted for three years during the vegetation period, and the bacterial community structure was assessed with cultivation-dependent approach. Many Gram-negative isolates (n = 251) from the rhizosphere survived sub culturing and were identified by biochemical tests. A total of 57 species belonging to 29 genera were identified and assigned to four broad taxonomic groups (Bacteroidetes, Alpha-, Beta- and Gamma-proteobacteria). Several specific bacterial cluster communities were identified inside all the three rhizospheres. Most of the species belonged to the genera Moraxella, Pseudomonas, Pantoea, Enterobacter and Acinetobacter. In addition, while, using the plate count analysis, large discrepancies in numbers among physiological groups of bacteria cultured from three rhizosphere samples have not been revealed, more expressive distinctions among bacterial populations were obtained concerning the relative abundance of different genera, different taxonomic groups as well as different diversity indices. Furthermore, the number of cultured bacteria and their taxonomic distribution in the rhizosphere of all three plants changed not only explicitly during vegetation period but continually during the three years of investigation. It seems that rhizosphere bacterial populations of each plant are under the influence of the specific root-released materials.     

Heterologous Escherichia coli Expression, Purification and Characterization of the GrmA Aminoglycoside-Resistance Methyltransferase

The mechanism of resistance to aminoglycosides based on methylation of their target, 16S rRNA, was until recently described only in antibiotic producing microorganisms. However, equivalent methyltransferases have now also been identified among numerous clinical Gram-negative pathogenic isolates. We have cloned, expressed, and purified GrmA, the aminoglycoside-resistance methyltransferase from Micromonospora purpurea, producer of gentamicin complex. Two vectors were created that express protein with an N-terminal 6× histidine tag with and without an enterokinase recognition producing proteins His₆-EK-GrmA and His₆-GrmA, respectively. The activity of both recombinant proteins was demonstrated in vivo. After optimized expression and native purification both protein variants proved to be active in in vitro methylation assays. This work lays a foundation for future detailed biochemical, structural and pharmacological studies with this member of an important group of aminoglycoside-resistance enzymes.     

New names for homonyms in the genus Dactylogyrus Diesing, 1850 (Monogenea, Dactylogyridae)

The following new replacement names for homonyms in the genus Dactylogyrus Diesing are proposed: Dactylogyrus acrossocheili nom. nov. for D. forcipatus Wu & Wang, 1983; D. birgii nom. nov. for D. simplex Birgi & Lambert, 1987; D. cheni nom. nov. for D. orientalis Hu & Chen, 1979; D. hui nom. nov. for D. xenocypris Hu & Chen, 1979; D. limae nom. nov. for D. hamatus Chinabut & Lim, 1994; D. mikailovi nom. nov. for D. gracilis Mikailov, 1974; D. pakistanensis nom. nov. for D. mrigali Rizvi, 1978; D. papernai nom. nov. for D. magnum Paperna, 1973; D. saurogobii nom. nov. for D. falcatus Wu, Wang & Song, 1983; and D. semifasciolatae nom. nov. for D. lineatus Luo & Lang, 1982.