Influence of Two-Dimensional Black Phosphorus on the Horizontal Transfer of Plasmid-Mediated Antibiotic Resistance Genes: Promotion or Inhibition?

The problem of bacterial resistance caused by antibiotic abuse is seriously detrimental to global human health and ecosystem security. The two-dimensional nanomaterial (2D) such as black phosphorus (BP) is recently expected to become a new bacterial inhibitor and has been widely used in the antibacterial field due to its specific physicochemical properties. Nevertheless, the effects of 2D-BP on the propagation of antibiotic resistance genes (ARGs) in environments and the relevant mechanisms are not clear. Herein, we observed that the sub-inhibitory concentrations of 2D-BP dramatically increased the conjugative transfer of ARGs mediated by the RP4 plasmid up to 2.6-fold at the 125 mg/L exposure level compared with the untreated bacterial cells. Nevertheless, 2D-BP with the inhibitory concentration caused a dramatic decrease in the conjugative frequency. The phenotypic changes revealed that the increase of the conjugative transfer caused by 2D-BP exposure were attributed to the excessive reactive oxygen species and oxidative stress, and increased bacterial cell membrane permeability. The genotypic evidence demonstrated that 2D-BP affecting the horizontal gene transfer of ARGs was probably through the upregulation of mating pair formation genes (trbBp and traF) and DNA transfer and replication genes (trfAp and traJ), as well as the downregulation of global regulatory gene expression (korA, korB, and trbA). In summary, the changes in the functional and regulatory genes in the conjugative transfer contributed to the stimulation of conjugative transfer. This research aims to broaden our comprehension of how nanomaterials influence the dissemination of ARGs by elucidating their effects and mechanisms.

Transformation of sulfur species in lake sediments at Ardley Island and Fildes Peninsula, King George Island, Antarctic Peninsula.

In Antarctica, penguins transport sulfur and other bio-elements in the form of guano from marine to terrestrial environments where they become deposited in ornithogenic soils and sediments, including lake or pond systems. Transformation of sulfur species in these terrestrial and aquatic deposits, however, has rarely been studied. Here, we used the cold diffusion method to analyze various sulfur species in a lake deposit of ornithogenic sediment core (C1) and a pristine lake sediment core (C2), collected from Ardley Island and Fildes Peninsula, Antarctic Peninsula, respectively. The total organic carbon, total phosphorus, total nitrogen and various sulfur species in C1 were more fluctuant and much higher than those in C2, indicating a primary source from penguin guano. In core C1, organic sulfur (Org-S) was the main form of sulfur, and sulfate (SO42-) was the main form of inorganic sulfur. The acid volatile sulfur (AVS) in C1 was much higher than pyrite sulfur (CRS). In the pristine lake sediment core C2, Org-S and SO42- were the main sulfur species. CRS was the primary form of reduced inorganic sulfur in C2 sediments in contrast to the AVS in C1, indicating that AVS had been effectively transformed into CRS in C1. Our results demonstrate that the high levels of organic matter in C1 likely limited the transformation of AVS to CRS.

Restriction of sulfate reduction on the bioavailability and toxicity of trace metals in Antarctic lake sediments.

In this study, Acid-Volatile Sulfur (AVS), trace metals Cu, Cd and Zn and their chemical speciation based on BCR-sequential and simultaneous extraction (SEMs) in Antarctic lake sediments (Y2-1 and YO) were analyzed to investigate the restriction of sulfate reduction on the bioavailability and toxicity of trace metals. Much higher trace metals in Y2-1 indicating a primary source from penguin guano. The main chemical speciation of Cu and Cd in Y2-1 was their oxidizable fraction in contrast to those of weak-acid extraction in YO. Lower ratio of ΣSEM/AVS in Y2-1 indicating less toxicity of the trace metals. The main chemical speciation of Cd in Y2-1 was their oxidizable fraction in contrast to that exchangeable fraction in penguin guano, indicating that although amounts of Cd was transported from marine to lake by penguins, strong sulfate reduction in ornithogenic sediments restricts the bioavailability and toxicity of Cd through the formation of insoluble sulfide.

Levels, sources and influence mechanisms of heavy metal contamination in topsoils in Mirror Peninsula, East Antarctica.

Heavy metal contaminants in Mirror Peninsula, East Antarctica, have rarely been studied and the source and influencing factors are poorly understood. We sampled a grid of 189 topsoil samples from Mirror Peninsula and analyzed the concentrations of Zn, Cu, U, Cr, Ga, Pb, Hg, Se and As; we also calculated the chemical index of alteration (CIA), a proxy of weathering. The results show that the distributions of Cr, Ga, Cu, and Zn are associated with weathering; the distributions of As and Pb are related to vehicle use and unloading activities at the wharfs, respectively; and the distribution of Hg is likely associated with both anthropogenic impacts and biological activity. The contamination level of these heavy metals in Mirror Peninsula is relatively low and within the controllable range. Both weathering processes and anthropogenic impacts can cause the enrichment of heavy metals; thus reliable source apportionment is crucial in studying heavy metal enrichment and contamination.

Assessment of heavy metal contamination from penguins and anthropogenic activities on Fildes Peninsula and Ardley Island, Antarctic.

Fildes Peninsula, with a high density of scientific stations, has been significantly impacted by anthropogenic activities. However, the contamination from penguins, a biovector that transports pollutants from ocean to land, has seldom been assessed. In this study, 32 lacustrine surface sediment samples on Fildes Peninsula and 8 lacustrine surface sediment samples on Ardley Island were collected to determine Cu, Zn, Pb, Ni, Cr, Cd, Co, Sb, Hg and P levels. The results showed that the heavy metal contents of lacustrine sediments on Ardley Island are significantly higher than those on Fildes Peninsula. The contaminants on Fildes Peninsula are mainly derived from anthropogenic activities, while the contaminants on Ardley Island are transported to the lacustrine sediments in the form of penguin guanos after a series of biomagnification in the food chain. The results indicated that the impact of penguin-transported contamination on Antarctic environment outweighs human activities near scientific stations in some areas. Therefore, more attention should be paid to the impacts of Antarctic animals on the Antarctic environment.

Geochemical record of high emperor penguin populations during the Little Ice Age at Amanda Bay, Antarctica.

Emperor penguins (Aptenodytes forsteri) are sensitive to the Antarctic climate change because they breed on the fast sea ice. Studies of paleohistory for the emperor penguin are rare, due to the lack of archives on land. In this study, we obtained an emperor penguin ornithogenic sediment profile (PI) and performed geochronological, geochemical and stable isotope analyses on the sediments and feather remains. Two radiocarbon dates of penguin feathers in PI indicate that emperor penguins colonized Amanda Bay as early as CE 1540. By using the bio-elements (P, Se, Hg, Zn and Cd) in sediments and stable isotope values (δ(15)N and δ(13)C) in feathers, we inferred relative population size and dietary change of emperor penguins during the period of CE 1540-2008, respectively. An increase in population size with depleted N isotope ratios for emperor penguins on N island at Amanda Bay during the Little Ice Age (CE 1540-1866) was observed, suggesting that cold climate affected the penguin's breeding habitat, prey availability and thus their population and dietary composition.

Transport of nutrients and contaminants from ocean to island by emperor penguins from Amanda Bay, East Antarctic.

Penguins play important roles in the biogeochemical cycle between Antarctic Ocean and land ecosystems. The roles of emperor penguin Aptenodytes forsteri, however, are usually ignored because emperor penguin breeds in fast sea ice. In this study, we collected two sediment profiles (EPI and PI) from the N island near a large emperor penguin colony at Amanda Bay, East Antarctic and performed stable isotope and element analyses. The organic C/N ratios and carbon and nitrogen isotopes suggested an autochthonous source of organic materials for the sediments of EPI (C/N = 10.21 ± 0.28, n = 17; δ(13)C = -13.48 ± 0.50‰, δ(15)N = 8.35 ± 0.55‰, n = 4) and an allochthonous source of marine-derived organic materials for the sediments of PI (C/N = 6.15 ± 0.08, δ(13)C = -26.85 ± 0.11‰, δ(15)N = 21.21 ± 2.02‰, n = 20). The concentrations of total phosphorus (TP), selenium (Se), mercury (Hg) and zinc (Zn) in PI sediments were much higher than those in EPI, the concentration of copper (Cu) in PI was a little lower, and the concentration of element lead (Pb) showed no difference. As measured by the geoaccumulation indexes, Zn, TP, Hg and Se were from moderately to very strongly enriched in PI, relative to local mother rock, due to the guano input from juvenile emperor penguins. Because of its high trophic level and transfer efficiency, emperor penguin can transport a large amount of nutrients and contaminants from ocean to land even with a relatively small population, and its roles in the biogeochemical cycle between ocean and terrestrial environment should not be ignored.