Identification and Characterization of a Novel Aminoglycoside 3''-Nucleotidyltransferase, ANT(3'')-IId, From Acinetobacter lwoffii

A novel plasmid-encoded aminoglycoside 3''-nucleotidyltransferase ANT(3")-IId, was discovered in Acinetobacter lwoffi strain H7 isolated from a chick on an animal farm in Wenzhou, China. The whole-genome of A. lwoffii H7 consisted of one chromosome and five plasmids (pH7-250, pH7-108, pH7-68, pH7-48, and pH7-11). ant(3")-IId was identified as being encoded on pH7-250, sharing the highest amino acid identity of 50.64% with a function-known resistance gene, ant(3")-IIb (KB849358.1). Susceptibility testing and enzyme kinetic parameter analysis were conducted to determine the function of the aminoglycoside 3"-nucleotidyltransferase. The ant(3")-IId gene conferred resistance to spectinomycin and streptomycin [the minimum inhibitory concentration (MIC) levels of both increased 16-fold compared with the control strain]. Consistent with the MIC data, kinetic analysis revealed a narrow substrate profile including spectinomycin and streptomycin, with Kcat/Km ratios of 4.99 and 4.45×103M−1 S−1, respectively. Sequencing analysis revealed that the ant(3")-IId gene was associated with insertion sequences (IS) element [ΔISAba14-ΔISAba14-hp-orf-orf-orf1-ant(3")-IId], and ant(3")-IId were identified in plasmids from various Acinetobacter species. This study of the novel aminoglycoside 3"-nucleotidyltranferase ANT(3")-IId helps us further understand the functional and sequence characteristics of aminoglycoside 3"-nucleotidyltranferases, highlights the risk of resistance gene transfer among Acinetobacter species and suggests that attention should be given to the emergence of new aminoglycoside 3"-nucleotidyltranferase genes.

DETERMINING TEMPERATURE OPTIMA OF APPLE CULTIVARS AND ROOTSTOCKS BY THE TEMPERATURE-DEPENDENT REAPPEARANCE OF VARIABLE FLUORESCENCE FOLLOWING ILLUMINATION

Development of valid temperature-based models of physiological processes such as seed germination, bud development, vegetative growth, fruit development, or fruit maturation, requires a parameter to link temperature with plant metabolism. The Thermal Kinetic Window (TKW) concept uses the temperature characteristics of an enzyme kinetic parameter, the Michaelis constant (Km) as indicators of metabolic efficiency. Recently, Burke3 has shown that the temperature dependence of the rate and magnitude of the reappearance of photosystem II (PSII) variable fluorescence following illumination corresponded with the optimal temperature described by the TKW for several plant species. The present study investigated the use of the temperature sensitivity of PSII fluorescence in the identification of temperature optima of apple cultivars and rootstocks. 3Burke, J.J. 1990. Plant Physiol. 93:652-656.