SmvA, and not AcrB, is the major efflux pump for acriflavine and related compounds in Salmonella enterica serovar Typhimurium

Indexación: Scopus.Objectives: The aim was to study the role played by SmvA pump in the efflux of quaternary ammonium compounds (QACs) in Salmonella enterica serovar Typhimurium (Salmonella Typhimurium). Methods: Mutants in the smvA, acrB and tolC genes were constructed by the red swap method. P22 was used to transduce tolC to acrB and smvA mutant strains. The susceptibility of these strains to acriflavine and a variety of QACs was determined by MIC assays. Results: In comparison with the Salmonella Typhimurium wild-type strain, the smvA mutant was more susceptible to QACs than the acrB mutant strain. A tolC single mutant was more susceptible than an acrB mutant to QACs, acriflavine, ethidium bromide, malachite green and pyronin B. The tolC - acrB double mutant was as susceptible as the single tolC mutant to QACs. Additionally, the smvA mutant strain was more susceptible to acriflavine than the acrB mutant (MICs = 31.3 versus 125 mg/L, i.e. 4-fold). Finally, the tolC - smvA double mutant (3.9 mg/L) was approximately 10 times more susceptible to acriflavine than either smvA (31.3 mg/L) or tolC (31.3 mg/L) single mutants. Conclusions: It is the SmvA efflux pump, and not AcrB, that plays the major role in the efflux of acriflavine and other QACs from Salmonella Typhimurium. This apparently conflicting report is due to the fact that in Escherichia coli the smvA gene does not exist. Our results suggest that tolC and smvA genes encode components of two different efflux systems with overlapping specificities that work in parallel to export acriflavine and other QACs. © The Author 2008. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved.https://academic-oup-com.recursosbiblioteca.unab.cl/jac/article/62/6/1273/77164

Increased xylem ingestion and decreased phloem ingestion in the aphid Acyrthosiphon pisum (Hemiptera: Aphididae) parasitised by Aphidius ervi (Hymenoptera: Braconidae)

Ramirez, C.C. Centro de Investigación en Biotecnología Silvoagrícola, Instituto de Biología Vegetal y Biotecnología, Universidad de Talca, Casilla 747, Talca, ChileThe effects of parasitisation by Aphidius ervi on the feeding behaviour of the aphid Acyrthosiphon pisum were studied. There was progressive increase in the time devoted to xylem ingestion (G waveform) and concomitant decrease in time devoted to phloem ingestion (E2 waveform) in parasitized relative to unparasitized aphids, as the time from parasitisation increased. These changes are interpreted as a way aphids compensate for metabolic changes occurring during parasitisation

Antipredator responses of aphids to parasitoids change as a function of aphid physiological state

Ramirez, C.C.Centro de Investigaciones en Biotecnología Silvoagrícola, Universidad de TalcaUnder predation risk, prey may prioritize antipredator behaviours and sacrifice feeding. However, energetically constrained animals may choose to sacrifice or change antipredator responses and accept relatively greater risk in order to secure food. In this last case, the antipredator tactics chosen must balance safety and feeding in such a way that costs are minimized and benefits maximized. We studied the antipredator behaviour of pea aphid, Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae) subjected to different periods of food deprivation, against the parasitoid Aphidius ervi (Hymenoptera: Braconidae). As the energetic internal stress of aphids increased, the predominant antipredator response changed from walking away and dropping to kicking behaviour, and parasitization avoidance decreased. Parasitoids did not show preference between food-deprived and nonfood-deprived aphids. Dropping and walking away reduced parasitization from 50 to 33%. These results support the hypothesis that the antipredator behaviour of an aphid changes as a function of internal stress. By performing less costly behaviour such as kicking under energetically constrained conditions, aphids seem to minimize their probability of energy shortfall. Given that aphid antipredator behaviour is a function of nutritional state, its occurrence under natural conditions may match host quality spatial distribution. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved

Together we stand, divided we fall: Effects of livestock grazing on vegetation patches in a desert community

Questions Vegetation patches formed by interacting xeric species are the main drivers of dryland structure and function. Plant aggregation enhances microclimatic conditions and triggers abiotic and biotic processes, such as nutrient cycling and accumulation, and species interactions. However, vegetation patches may be modified by disturbances in unpredictable ways. We tested whether livestock grazing affects vegetation structure and plant spatial associations in a desert community, by considering the role of plant species in ecological succession. Location Patagonian Monte Desert, Argentina. Methods We used high-quality standardized photographs along transects to characterize plant community structure (i.e., cover, abundance, richness), spatial patterns (i.e. plant-plant associations), and classified species based on their successional role (i.e. early, intermediate and late species). We used regression models and network analysis to evaluate the effect of grazing on vegetation. Results In general, grazing modified community structure, reducing total cover, abundance and richness. Grazing modulated community spatial patterns, simplifying and removing vegetation patches. The impact of grazing depended on the species successional role. The abundance and cover of early species were less affected by grazing than intermediate and late species, the latter being the most affected. However, species richness significantly decreased with increasing stocking rates, regardless of their successional role. Late species were present in most plant spatial associations, indicating a major contribution to multi-specific vegetation patches formation. Conclusions The reduction in species richness and low abundance of late species highlights the need to prevent irreversible degradation caused by overgrazing. Late species emerge as key structures of vegetation in desert rangelands facilitating the establishment and protecting other plant species. Due to the critical role of vegetation patches in maintaining desert ecosystem functioning, conservation and management practices should focus on late species, while early species, responsible for vegetation patch formation in overgrazed situations, should be preferred for restoration practices