MRG Chip: A High-Throughput qPCR-Based Tool for Assessment of the Heavy Metal(loid) Resistome.

Bacterial metal detoxification mechanisms have been well studied for centuries in pure culture systems. However, profiling metal resistance determinants at the community level is still a challenge due to the lack of comprehensive and reliable quantification tools. Here, a novel high-throughput quantitative polymerase chain reaction (HT-qPCR) chip, termed the metal resistance gene (MRG) chip, has been developed for the quantification of genes involved in the homeostasis of 9 metals. The MRG chip contains 77 newly designed degenerate primer sets and 9 published primer sets covering 56 metal resistance genes. Computational evaluation of the taxonomic coverage indicated that the MRG chip had a broad coverage matching 2 kingdoms, 29 phyla, 64 classes, 130 orders, 226 families, and 382 genera. Temperature gradient PCR and HT-qPCR verified that 57 °C was the optimal annealing temperature, with amplification efficiencies of over 94% primer sets achieving 80-110%, with R2 > 0.993. Both computational evaluation and the melting curve analysis of HT-qPCR validated a high specificity. The MRG chip has been successfully applied to characterize the distribution of diverse metal resistance determinants in natural and human-related environments, confirming its wide scope of application. Collectively, the MRG chip is a powerful and efficient high-throughput quantification tool for exploring the microbial metal resistome.

Differences in cadmium absorption by 71 leaf vegetable varieties from different families and genera and their health risk assessment.

Leaf vegetables have strong capabilities to take up cadmium (Cd) compared to other vegetable varieties. Until now, the differences in Cd uptake and accumulation by leaf vegetables from different families and genera and the related health risks were unknown. To remedy this, we studied 71 leaf vegetables (multiple genotypes within 17 categories of vegetables) in soil cultivation experiments (3 Cd treatment levels). Results showed that at 2.12 mg kg-1 Cd treatment, the dry weight of only five genotypic varieties from the families Brassicaceae and Asteraceae significantly decreased compared to the control, suggesting their weak Cd tolerances. Vegetables from the Brassicaceae, Asteraceae, Apiaceae, and Convolvulaceae families had stronger Cd absorption capabilities, whereas those from the Liliaceae and Amaranthaceae families had weaker ones. Cluster analysis found that the 17 vegetable categories could be divided into three groups: vegetables with high Cd accumulation capabilities were Lactuca sativa L.var. ramosa Hort. and Lactuca sativa var. longifoliaf. Lam. Vegetables with moderate Cd accumulation capabilities were bok choy, napa cabbage, choy sum, leaf mustard, Lactuca sativa L., Sonchus oleraceus L., celery, coriander, and water spinach. Vegetables with low Cd accumulation capabilities were cabbage, crown daisy, garlic chive, Allium ascalonicum, Gynura cusimbua, and edible amaranth. Estimated daily intake (EDI) and target hazard quotient (THQ) analysis results showed that 100% genotypes of vegetables from the Apiaceae and Convolvulaceae families had health risks; 100% genotypes of Lactuca sativa L., Sonchus oleraceus L., Lactuca sativa L. var. ramosa Hort., and Lactuca sativa var. longifoliaf. Lam from the Asteraceae family carried high risks. Of vegetables in the Brassicaceae family, 42.9% showed risks. Vegetables from the Amaranthaceae and Liliaceae families, Gynura cusimbua and crown daisy from the Asteraceae family, and cabbage from the Brassicaceae family all displayed relatively low risks (all 100%).

Assessment of tea garden soils at An'xi County in southeast China reveals a mild threat from contamination of potentially harmful elements.

An extensive study of the spatial distribution characteristics of potentially harmful elements (PHEs) in tea (Camellia sinensis (L.) O. Kuntze) garden soils and ecological risk assessment at An'xi County, the birthplace of oolong tea in China, was implemented. A total of 78 soil samples were examined to determine the concentration of five PHEs (As, Cd, Cr, Hg and Pb), soil organic matter and pH by using geostatistical approaches combined with geographical information system analysis. All PHEs presented in the study area were slightly higher than their background values for provincial and national standards except Cr. Moreover, ecological risk assessment of PHEs in the tea garden soils at An'xi County was performed by means of the Håkanson method. The average ecological potential risk index (Er) of the five PHEs followed a descending order of Cd > Hg > Pb > As > Cr, and suggested a moderate ecological risk in the study area.