Cadmium-dependent expression of a new metallothionein identified in Trichomonas vaginalis.

Metallothioneins (MTs) have been identified in a wide variety of organisms from bacteria to humans. The biological functions of these MTs have a key role in metalloregulatory metabolism and its expression is induced in response to different stimuli, particularly by divalent metal cations. Also, the action of MTs have been implicated in the survival of pathogens in presence of microbicidal concentration of divalent cations, which allows the establishment of the infection. Trichomonas vaginalis is a protozoan parasite that adapts to the microenvironment of the male urogenital tract, where cations such as zinc (Zn2+) and cadmium (Cd2+) are present. Nevertheless, the molecular mechanisms of metal tolerance and homeostasis is not yet dilucidated in this parasite. In this study, we have identified 4 potential MT-like sequences (tvmt´s) in T. vaginalis genome. Because tvmt-2, -3, and -4 corresponds to truncated partial genes, we characterized the trichomonad tvmt-1 gene. The bioinformatic analyses and the predicted protein (TvMT-1) show similar properties to the reported in other MTs. The expression patterns of tvmt-1 in the presence of several divalent cations (Fe2+, Mn2+, Zn2+ and Cd2+) were analyzed and we demonstrated that Cd2+ induce significantly their expression. By indirect immunofluorescence assays, we corroborated this positive regulation of TvMT-1 in the cytoplasm of parasites grown in the presence of Cd2+. The tvmt-1 promoter contains putative metal responsive elements, which are probably the responsible for the Cd2+-dependent expression of this gene. Our results suggest that tvmt-1 gene encode a metallothionein that may be responsible for the homeostatis and detoxification of Cd+2 in T. vaginalis.

Dynamics of Huanglongbing-associated Bacterium Candidatus Liberibacter asiaticus in Citrus aurantifolia Swingle (Mexican Lime).

BACKGROUND: The bacterial disease citrus huanglongbing (HLB), associated with "Candidatus Liberibacter asiaticus" (C.Las) has severely impacted the citrus industry, causing a significant reduction in production and fruit quality. In the present study, it was monitored the C.Las population dynamics in symptomatic, HLB-positive Mexican lime trees (Citrus aurantifolia Swingle) in a tropical, citrus-producing area of Mexico. The objective of this study was to identify the dynamics of the population of huanglongbing-associated bacterium Candidatus Liberibacter asiaticus and its insect vector in Citrus aurantifolia Swingle (Mexican lime). MATERIALS AND METHODS: Leaf samples were collected every 2 months over a period of 26 months for quantification of bacterial titers and young and mature leaves were collected in each season to determine preferential sites of bacterial accumulation. The proportion of living and dead bacterial cells could be determined through the use of quantitative real-time PCR in the presence of ethidium monoazide (EMA-qPCR). RESULTS: It was observed a lower bacterial titer at high temperatures in the infected trees relative to titers in mild weather, despite a higher accumulation of the insect vector Diaphorina citri in these conditions. This study also revealed seasonal fluctuations in the titers of bacteria in mature leaves when compared to young leaves. No statistically significant correlation between any meteorological variable, C.Las concentration and D. citri population could be drawn. CONCLUSION: Although, HLB management strategies have focused on vector control, host tree phenology may be important. The evaluation of citrus phenology, C.Las concentration, ACP population and environmental conditions provides insights into the cyclical, seasonal variations of both the HLB pathogen and its vector. These findings should help in the design of integrative HLB control strategies that take into account the accumulation of the pathogen and the presence of its vector.