Genomic Islands Confer Heavy Metal Resistance in Mucilaginibacter kameinonensis and Mucilaginibacter rubeus Isolated from a Gold/Copper Mine.

Heavy metals (HMs) are compounds that can be hazardous and impair growth of living organisms. Bacteria have evolved the capability not only to cope with heavy metals but also to detoxify polluted environments. Three heavy metal-resistant strains of Mucilaginibacer rubeus and one of Mucilaginibacter kameinonensis were isolated from the gold/copper Zijin mining site, Longyan, Fujian, China. These strains were shown to exhibit high resistance to heavy metals with minimal inhibitory concentration reaching up to 3.5 mM Cu(II), 21 mM Zn(II), 1.2 mM Cd(II), and 10.0 mM As(III). Genomes of the four strains were sequenced by Illumina. Sequence analyses revealed the presence of a high abundance of heavy metal resistance (HMR) determinants. One of the strain, M. rubeus P2, carried genes encoding 6 putative PIB-1-ATPase, 5 putative PIB-3-ATPase, 4 putative Zn(II)/Cd(II) PIB-4 type ATPase, and 16 putative resistance-nodulation-division (RND)-type metal transporter systems. Moreover, the four genomes contained a high abundance of genes coding for putative metal binding chaperones. Analysis of the close vicinity of these HMR determinants uncovered the presence of clusters of genes potentially associated with mobile genetic elements. These loci included genes coding for tyrosine recombinases (integrases) and subunits of mating pore (type 4 secretion system), respectively allowing integration/excision and conjugative transfer of numerous genomic islands. Further in silico analyses revealed that their genetic organization and gene products resemble the Bacteroides integrative and conjugative element CTnDOT. These results highlight the pivotal role of genomic islands in the acquisition and dissemination of adaptive traits, allowing for rapid adaption of bacteria and colonization of hostile environments.

6-OHBDE-47 induces transcriptomic alterations of CYP1A1, XRCC2, HSPA1A, EGR1 genes and trigger apoptosis in HepG2 cells.

In this study, HepG2 cells were exposed to 6-hydroxy- 2,2',4,4'-tetrabromodiphenyl ether (6-OH-BDE-47) for 3 and 6 days for monitoring cytotoxic effects and alterations in its transcriptomic profile. MTT assay showed that cells exposed to 6-OH-BDE-47 (50 nM) exhibited 48.5% and 53.7% decline in cell survival after 3 and 6 days. Neutral red uptake (NRU) assay also demonstrated 47.1% and 56% reduction in cell survival at 50 nM, indicating lysosomal toxicity. The flow cytometric data confirmed an increase in intracellular reactive oxygen species (ROS) and mitochondrial dysfunction (ΔΨm). In comet assay, HepG2 cells exposed to 6-OH-BDE-47 (50 nM) showed 7.6-fold greater DNA damage. Cell cycle data revealed G2/M arrest at 10 and 25 nM after 3 days of exposure, while 50 nM induced mild apoptotic effect. The intensity of apoptosis increased after 6 days of exposure with 21.5%, 47% and 99.1% of cells recorded in subG1 apoptotic phase vis-à- vis the control showed 14.5% background apoptotic cells. Transcriptome analysis of 6-OH-BDE-47 (25 nM, 3 days) treated cells revealed cross talk between vital pathways. Especially, the genes involved in oxidative or metabolic stress, heat shock, growth arrest and senescence were differentially up- and down regulated to orchestrate the cellular toxicity and triggering apoptosis in HepG2 cells.