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DnaK protein alleviates toxicity induced by citrate-coated gold nanoparticles in Escherichia coli.

Makumire S, Revaprasadu N, Shonhai A - PLoS ONE (2015)

Bottom Line: We further investigated the effects of the AuNPs on the solubility of the E. coli BB1553 proteome.The toxic effects of the AuNPs were alleviated by transforming the E. coli BB1553 cells with a construct expressing DnaK.Our study suggests a role for DnaK in alleviating nanoparticle induced stress in E. coli.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, School of Mathematics & Natural Sciences, University of Venda, Thohoyandou, South Africa; Department of Biochemistry & Microbiology, University of Zululand, KwaDlangezwa, South Africa.

ABSTRACT
A number of previously reported studies suggest that synthetic gold nanoparticles (AuNPs) are capable of stabilising proteins against heat stress in vitro. However, it remains to be understood if AuNPs confer stability to proteins against cellular stress in vivo. Heat shock proteins (Hsps) are conserved molecules whose main role is to facilitate folding of other proteins (chaperone function). Hsp70 (called DnaK in prokaryotes) is one of the most prominent molecular chaperones. Since gold nanoparticles exhibit chaperone-like function in vitro, we investigated the effect of citrate-coated gold nanoparticles on the growth of E. coli BB1553 cells that possess a deleted dnaK gene. We further investigated the effects of the AuNPs on the solubility of the E. coli BB1553 proteome. E. coli BB1553 cells exposed to AuNPs exhibited cellular defects such as filamentation and plasma membranes pulled off the cell wall. The toxic effects of the AuNPs were alleviated by transforming the E. coli BB1553 cells with a construct expressing DnaK. We also noted that cells in which DnaK was restored exhibited distinct zones to which the nanoparticles were restricted. Our study suggests a role for DnaK in alleviating nanoparticle induced stress in E. coli.

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Comparative analysis of the effects of citrate AuNPs on E. coli DnaK- and E. coli DnaK+ cells.TEM images showing E. coli DnaK- and E. coli DnaK+ cells exposed to citrate-AuNPs. A comparative population overview of E. coli DnaK- cells cultured in the presence of AuNPs is shown (panel A1) versus E. coli DnaK+ cells cultured under similar conditions (panel A2). Panels B1-B2 and C1-C2 illustrate comparative morphological features of E. coli DnaK- cells versus E. coli DnaK+ cells, respectively. AuNP aggregates are seen as black spots inside the cells. Note the evident delineation zones in panels C2 and D2, associated with E. coli DnaK+ cells that are missing in E. coli DnaK- cells (panels C1and D1).
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pone.0121243.g003: Comparative analysis of the effects of citrate AuNPs on E. coli DnaK- and E. coli DnaK+ cells.TEM images showing E. coli DnaK- and E. coli DnaK+ cells exposed to citrate-AuNPs. A comparative population overview of E. coli DnaK- cells cultured in the presence of AuNPs is shown (panel A1) versus E. coli DnaK+ cells cultured under similar conditions (panel A2). Panels B1-B2 and C1-C2 illustrate comparative morphological features of E. coli DnaK- cells versus E. coli DnaK+ cells, respectively. AuNP aggregates are seen as black spots inside the cells. Note the evident delineation zones in panels C2 and D2, associated with E. coli DnaK+ cells that are missing in E. coli DnaK- cells (panels C1and D1).

Mentions: E. coli DnaK- cells that were cultured in the presence of 40 μgmL-1 citrate AuNPs exhibiting various stages of cell deformity were observed by TEM (Fig. 2). It has been previously demonstrated that AuNPs are readily internalised by E. coli cells [10][11]. The internalisation of AuNPs by the E. coli DnaK- cells was evident (Fig. 2) and the nanoparticles appeared to complex with cytoplasmic material, leading to cell death. Comparative TEM views of E. coli DnaK- cells versus E. coli DnaK+ cells cultured in the presence of AuNPs show distinct features between the two groups of cells (Fig. 3). While a few nanoparticles were internalised as single entities, most of the AuNPs appeared in agglomerations in the cells. Based on TEM images, there is evidence that the AuNPs complexed with the cytosolic material both in DnaK- and DnaK+E. coli cells. Both E. coli DnaK+ cells and E. coli DnaK- cells exposed to AuNPs at 30°C had cells of normal shape and size as well as some that had filamented (Fig. 3, panels A1; A2). However, a higher proportion of filamented cells were observed in the E. coli DnaK- sample. Filamentation of bacteria is associated with cellular stress and DnaK deficiency promotes this phenomenon [23]. It is possible that the filamentation observed in some cells from the E. coli DnaK+ cell population may have been induced by AuNP toxicity. We also noticed that a large proportion of E. coli DnaK- cells had invaginations and their plasma membranes pulled off from the cell wall (Fig. 3; panels B1-B2; C1-C2). However, a large proportion of E. coli DnaK+ cells exhibited normal cellular integrity. We also noticed distinct “zones” that confined the nanoparticles to specific sites within the cytosol of E. coli DnaK+ cells (Fig. 3; panels C1-C2; D1-D2). It is not clear what role DnaK played in the development of these distinct structural features. However, it is evident that DnaK was involved in the development of these features, as E. coli DnaK- cells did not exhibit similar features. As a result, most of the E. coli DnaK- cells did not appear to restrict the localisation of the AuNP nucleation zones to specific locations within the cell (Fig. 3; panels D1-D2).


DnaK protein alleviates toxicity induced by citrate-coated gold nanoparticles in Escherichia coli.

Makumire S, Revaprasadu N, Shonhai A - PLoS ONE (2015)

Comparative analysis of the effects of citrate AuNPs on E. coli DnaK- and E. coli DnaK+ cells.TEM images showing E. coli DnaK- and E. coli DnaK+ cells exposed to citrate-AuNPs. A comparative population overview of E. coli DnaK- cells cultured in the presence of AuNPs is shown (panel A1) versus E. coli DnaK+ cells cultured under similar conditions (panel A2). Panels B1-B2 and C1-C2 illustrate comparative morphological features of E. coli DnaK- cells versus E. coli DnaK+ cells, respectively. AuNP aggregates are seen as black spots inside the cells. Note the evident delineation zones in panels C2 and D2, associated with E. coli DnaK+ cells that are missing in E. coli DnaK- cells (panels C1and D1).
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Related In: Results  -  Collection

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pone.0121243.g003: Comparative analysis of the effects of citrate AuNPs on E. coli DnaK- and E. coli DnaK+ cells.TEM images showing E. coli DnaK- and E. coli DnaK+ cells exposed to citrate-AuNPs. A comparative population overview of E. coli DnaK- cells cultured in the presence of AuNPs is shown (panel A1) versus E. coli DnaK+ cells cultured under similar conditions (panel A2). Panels B1-B2 and C1-C2 illustrate comparative morphological features of E. coli DnaK- cells versus E. coli DnaK+ cells, respectively. AuNP aggregates are seen as black spots inside the cells. Note the evident delineation zones in panels C2 and D2, associated with E. coli DnaK+ cells that are missing in E. coli DnaK- cells (panels C1and D1).
Mentions: E. coli DnaK- cells that were cultured in the presence of 40 μgmL-1 citrate AuNPs exhibiting various stages of cell deformity were observed by TEM (Fig. 2). It has been previously demonstrated that AuNPs are readily internalised by E. coli cells [10][11]. The internalisation of AuNPs by the E. coli DnaK- cells was evident (Fig. 2) and the nanoparticles appeared to complex with cytoplasmic material, leading to cell death. Comparative TEM views of E. coli DnaK- cells versus E. coli DnaK+ cells cultured in the presence of AuNPs show distinct features between the two groups of cells (Fig. 3). While a few nanoparticles were internalised as single entities, most of the AuNPs appeared in agglomerations in the cells. Based on TEM images, there is evidence that the AuNPs complexed with the cytosolic material both in DnaK- and DnaK+E. coli cells. Both E. coli DnaK+ cells and E. coli DnaK- cells exposed to AuNPs at 30°C had cells of normal shape and size as well as some that had filamented (Fig. 3, panels A1; A2). However, a higher proportion of filamented cells were observed in the E. coli DnaK- sample. Filamentation of bacteria is associated with cellular stress and DnaK deficiency promotes this phenomenon [23]. It is possible that the filamentation observed in some cells from the E. coli DnaK+ cell population may have been induced by AuNP toxicity. We also noticed that a large proportion of E. coli DnaK- cells had invaginations and their plasma membranes pulled off from the cell wall (Fig. 3; panels B1-B2; C1-C2). However, a large proportion of E. coli DnaK+ cells exhibited normal cellular integrity. We also noticed distinct “zones” that confined the nanoparticles to specific sites within the cytosol of E. coli DnaK+ cells (Fig. 3; panels C1-C2; D1-D2). It is not clear what role DnaK played in the development of these distinct structural features. However, it is evident that DnaK was involved in the development of these features, as E. coli DnaK- cells did not exhibit similar features. As a result, most of the E. coli DnaK- cells did not appear to restrict the localisation of the AuNP nucleation zones to specific locations within the cell (Fig. 3; panels D1-D2).

Bottom Line: We further investigated the effects of the AuNPs on the solubility of the E. coli BB1553 proteome.The toxic effects of the AuNPs were alleviated by transforming the E. coli BB1553 cells with a construct expressing DnaK.Our study suggests a role for DnaK in alleviating nanoparticle induced stress in E. coli.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, School of Mathematics & Natural Sciences, University of Venda, Thohoyandou, South Africa; Department of Biochemistry & Microbiology, University of Zululand, KwaDlangezwa, South Africa.

ABSTRACT
A number of previously reported studies suggest that synthetic gold nanoparticles (AuNPs) are capable of stabilising proteins against heat stress in vitro. However, it remains to be understood if AuNPs confer stability to proteins against cellular stress in vivo. Heat shock proteins (Hsps) are conserved molecules whose main role is to facilitate folding of other proteins (chaperone function). Hsp70 (called DnaK in prokaryotes) is one of the most prominent molecular chaperones. Since gold nanoparticles exhibit chaperone-like function in vitro, we investigated the effect of citrate-coated gold nanoparticles on the growth of E. coli BB1553 cells that possess a deleted dnaK gene. We further investigated the effects of the AuNPs on the solubility of the E. coli BB1553 proteome. E. coli BB1553 cells exposed to AuNPs exhibited cellular defects such as filamentation and plasma membranes pulled off the cell wall. The toxic effects of the AuNPs were alleviated by transforming the E. coli BB1553 cells with a construct expressing DnaK. We also noted that cells in which DnaK was restored exhibited distinct zones to which the nanoparticles were restricted. Our study suggests a role for DnaK in alleviating nanoparticle induced stress in E. coli.

No MeSH data available.


Related in: MedlinePlus