ABSTRACT
The heavy metal cadmium (Cd) is a toxic and bioaccumulative metal that can be enriched in the tissues and organs of living organisms through the digestive tract. However, more research is needed to determine whether food-sourced Cd affects the homeostasis of host gut microflora. In this study, the snail Bradybaena ravida (Benson) was used as a model organism fed with mulberry leaves spiked with different concentrations of Cd (0, 0.052, 0.71, and 1.94 mg kg-1). By combining 16S rRNA high-throughput sequencing with biochemical characterization, it was found that there were increases in the overall microbial diversity and abundances of pathogenic bacteria such as Corynebacterium, Enterococcus, Aeromonas, and Rickettsia in the gut of B. ravida after exposure to Cd. However, the abundances of potential Cd-resistant microbes in the host's gut, including Sphingobacterium, Lactococcus, and Chryseobacterium, decreased with increasing Cd concentrations in the mulberry leaves. In addition, there was a significant reduction in activities of energy, nutrient metabolism, and antioxidant enzymes for gut microbiota of snails treated with high concentrations of Cd compared to those with low ones. These findings highlight the interaction of snail gut microbiota with Cd exposure, indicating the potential role of terrestrial animal gut microbiota in environmental monitoring through rapid recognition and response to environmental pollution.
ABSTRACT
Hitherto, research on iron(III)-reduction has mainly focused on bacteria rather than fungal communities. To acquire insight into fungi involved in iron(III) reduction, typical organic matters (containing cellulose, glucose, lactate, and acetate) and ferrihydrite were used as electron donors and acceptors, respectively, in the presence of antibiotics. After antibiotic addition, microbial iron(III) reduction was still detected at quite high rates. In comparison, rates of iron(III) reduction were significantly lower in cellulose-amended groups than those with glucose, lactate, and acetate under the antibiotic-added condition. Patterns of intermediate (e.g., acetate, pyruvate, glucose) turnover were markedly different between treatments with and without antibiotics during organic degradation. A total of 20 genera of potential respiratory and fermentative iron(III)-reducing fungi were discovered based on ITS sequencing and genome annotation. This study provided an insight into the diversity of iron(III)-reducing fungi, indicating the underestimated contribution of fungi to iron and the coupled carbon biogeochemical cycling in environments.
