Lead is among the most common toxic heavy metals and its contamination is of great public concern. Bacillus coagulans is the probiotic which can be considered as the lead absorption sorbent to apply in the lead contaminant water directly or indirectly. A better understanding of the lead resistance and tolerance mechanisms of B. coagulans would help further its development and utilization. Wild-type Bacillus coagulans strain R11 isolated from a lead mine, was acclimated to lead-containing culture media over 85 passages, producing two lead-adapted strains, and the two strains shown higher lead intracellular accumulation ability (38.56-fold and 19.36-fold) and reducing ability (6.94-fold and 7.44-fold) than that of wild type. Whole genome sequencing, genome resequencing, and comparative transcriptomics identified lead resistance and tolerance process significantly involved in these genes which regulated glutathione and sulfur metabolism, flagellar formation and metal ion transport pathways in the lead-adapted strains, elucidating the relationships among the mechanisms regulating lead deposition, deoxidation, and motility and the evolved tolerance to lead. In addition, the B. coagulans mutants tended to form flagellar and chemotaxis systems to avoid lead ions rather than export it, suggesting a new resistance strategy. Based on the present results, the optimum lead concentration in environment should be considered when employed B. coagulans as the lead sorbent, due to the bacteria growth ability decreased in high lead concentration and physiology morphology changed could reduce the lead removal effectiveness. The identified deoxidization and compound secretion genes and pathways in B. coagulans R11 also are potential genetic engineering candidates for synthesizing glutathione, cysteine, methionine, and selenocompounds.
Gills are the main respiratory organs of fish and bear important physiological and immunological functions, but the functional heterogeneity of interlamellar cell mass (ILCM) at the single-cell level has rarely been reported. Here, we identified 19 cell types from the gills of crucian carp (Carassius auratus) by single-cell RNA sequencing (scRNA-seq) in combination with histological analysis. We annotated ILCM and analyzed its functional heterogeneity at the single-cell level for the first time. Functional enrichment analysis and cell cycle analysis identified ILCM as a type of metabolically active cells in a state of constant proliferation, and identified the major pathways responsible for ILCM immunoregulation. Histological analysis revealed the morphology and positional relationships of 6 cell types. Meanwhile, the gene regulatory network of ILCM was established through weighted gene co-expression network analysis (WGCNA), and one transcription factor and five hub genes related to immunoregulation were identified. We found that pyroptosis might be an important pathway responsible for the immune response of ILCM. Our findings provide an insight into the physiological and immune functions of gills and ILCM at the single-cell level and lay a solid foundation for further exploration of the molecular mechanism of ILCM immunity functions.
Mandarin fish (Siniperca chuatsi) is a voracious carnivorous species, usually consuming only live bait fish, but dietary acclimation enables it to accept artificial feed. However, the effects of dietary acclimation on intestinal performance and gene expression in mandarin fish and related mechanisms remain largely unknown. Therefore, this study investigated the effects of artificial feed on intestinal physicochemical and biochemical performance and gene expression in mandarin fish. Mandarin fish were sampled on day 10 after feeding with live dace (LD), at day 40 after subsequent feeding with dead dace plus artificial feed (DD + AF) from day 11 to day 40, and at day 90 after continuous feeding with artificial feed (AF) alone from day 41 to day 90 for transcriptome sequencing. The biochemical analysis results indicated that artificial feed significantly increased the activity of antioxidant enzymes glutathione peroxidase and superoxide dismutase in the intestine, liver, and stomach. Histological analysis demonstrated intestinal damage in mandarin fish fed with artificial feed. The GO and KEGG enrichment analyses indicated that the DEGs in AF vs. DD + AF were significantly enriched in the pentose phosphate pathway, and the DEGs in AF vs. LD were mainly significantly enriched in glycolysis/gluconeogenesis and PPAR signaling pathways. Nineteen feed acclimation-related key genes such as gene pfkfb4a and scd were identified in the intestine and found to exhibit upregulated expressions. These results revealed that artificial feed domestication enhanced the antioxidant capacity of the mandarin fish intestine and reduced hepatic lipid deposition by upregulating the related gene expression of mandarin fish and that the regulation of carbon metabolisms, including sugar, lipid, and steroid metabolisms, might be fundamental mechanisms for mandarin fish to acclimatize to dietary changes. These findings provide novel insights into the feed acclimation mechanism of mandarin fish, holding implications for promoting large-scale artificial feed aquaculture of mandarin fish and improving economic efficiency.