Cadmium stress triggers significant metabolic reprogramming in Enterococcus faecium CX 2-6

New complete genome insights into Enterobacter roggenkampii FACU2: a potential player in cadmium bio-removal

Industrial workplaces, particularly those involved in ore processing or smelting, pose a high risk of exposure to cadmium, a highly toxic metal. This study isolated and identified eight cadmium-resistant strains from industrial wastewater for their ability to resist cadmium. Enterobacter roggenkampii FACU2 demonstrated exceptional cadmium removal capabilities during our analysis, successfully eliminating 62% of the cadmium. Additionally, transmission electron microscopy (TEM) was utilized to examine the morphological change between the most and least efficient strains that responded to cadmium stress at the cellular level. Compared to the control bacteria, the treated bacteria exhibited notably higher levels of cadmium adsorption and accumulation within their cells. A complete genome analysis revealed that E. roggenkampii FACU2 has one chromosome and one plasmid with a size of 4,856,454 bp and 80,926 bp, respectively, in addition to harboring numerous heavy metal-resistant genes related to cadmium and other heavy metals. Moreover, the gene expression of four cadmium-resistant genes (czcA, cadA, czcC and czcD) showed that the high cadmium concentration led to a significant increase in czcA and cadA mRNA levels, thus indicating the activation of cadmium-resistant genes in the E. roggenkampii FACU2 compared to Enterobacter sp. strain FACU. Due to its ability to remove cadmium and other heavy metals, this strain holds promise as a source of genes for biological treatment methods. This application could contribute to environmental purification, ultimately benefiting human health.

Toxicity of cadmium on dynamic human gut microbiome cultures and the protective effect of cadmium-tolerant bacteria autochthonous to the gut

Cadmium (Cd) is a heavy metal toxic to the gut microbiome. In this study, we cultivated two human gut microbiomes (A and B) in bioreactors with Cd at 0 and 20 ppm for 7 days to investigate effects of Cd on the gut microbiome and to isolate Cd-tolerant bacteria autochthonous to the gut. Cd showed profound toxicity, abolishing butyrate production, depleting microbes in microbiome B, and simplifying microbiome A to a small Cd-tolerant community after 2 d of incubation. When spiked into the Cd-sensitive microbiome B, the Cd-tolerant community from microbiome A and isolates from that community worked synergistically with microbiome B to enhance butyrate production and maintained this synergism at Cd concentrations up to 5 ppm. Bacteria isolated from this Cd-tolerant community included Enterococcus faecium, Enterobacter cloacae, Lactococcus lactis, and Lactobacillus taiwanensis species. This work demonstrates a straightforward method for identifying Cd-tolerant bacteria autochthonous to the human gut that synergize with the microbiome to protect against Cd-related loss of butyrate production.

Soil microbial community assembly model in response to heavy metal pollution

Heavy metal pollution affected the stability and function of soil ecosystem. The impact of heavy metals on soil microbial community and the interaction of microbial community has been widely studied, but little was known about the response of community assembly to the heavy metal pollution. In this study, we collected 30 soil samples from non (CON), moderately (CL) and severely (CH) contaminated fields. The prokaryotic community was studied using high-throughput Illumina sequencing of 16s rRNA gene amplicons, and community assembly were quantified using phylogenetic-bin-based null approach (iCAMP). Results showed that diversity and composition of both bacterial and archaeal community changed significantly in response to heavy metal pollution. The microbial community assembly tended to be more deterministic with the increase of heavy metal concentration. Among the assembly processes, the relative importance of homogeneous selection (deterministic process) increased significantly (increased by 16.2%), and the relative importance of drift and dispersal limitation (stochastic process) decreased significantly (decreased by 11.4% and 5.4%, respectively). The determinacy of bacterial and archaeal community assembly also increased with heavy metal stress, but the assembly models were different. The deterministic proportion of microorganisms tolerant to heavy metals, such as Thiobacillus, Euryarchaeota and Crenarchaeota (clustered in bin 32, bin59 and bin60, respectively) increased, while the stochastic proportion of microorganisms sensitive to heavy metals, such as Koribacteraceae (clustered in bin23) increased. Therefore, the heavy metal stress made the prokaryotic community be deterministic, however, the effects on the assembly process of different microbial groups differed obviously.