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, 162 (2), 108-16

Environmental Factors Affecting Indole Production in Escherichia Coli

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Environmental Factors Affecting Indole Production in Escherichia Coli

Thi Hiep Han et al. Res Microbiol.

Abstract

A variety of both Gram-positive and Gram-negative bacteria produce large quantities of indole as an intercellular signal in microbial communities. Biosynthesis of indole is well-studied, and while carbon sources and amino acids are important environmental cues for indole production in Escherichia coli, other environmental factors affecting indole production for this strain are less clear. This study demonstrates that the environmental cue pH is an important factor for indole production that further controls biofilm formation of E. coli. Moreover, E. coli produced a higher level of extracellular indole in the presence of the antibiotics ampicillin and kanamycin, and the increased indole enhanced cell survival during antibiotic stress. Additionally, we found here that temperature is another important factor for indole production; E. coli produces and accumulates a large amount of indole at 50 °C, even at low cell densities. Overall, our results suggest that indole is a stable biological compound, and E. coli may utilize indole to protect itself against other microorganisms.

Figures

Fig. 1
Fig. 1
Effect of pH on extracellular indole production (A) and biofilm formation after 24 h (B) in E. coli in LB medium. pH (5, 6, 7, 8, and 9) was adjusted with 37% HCl and 5 N NaOH and cells were cultured at 30°C and 37°C. Extracellular indole was measured at a cell turbidity (optical density at 600 nm) of 1.5. The pH at the cell turbidity of 1.5 was almost same as the initial pH. Total biofilm (OD540) was normalized by cell growth (OD620) for each condition. Each data point was averaged from at least two independent cultures and one standard deviation is shown.
Fig. 2
Fig. 2
Effect of antibiotics on extracellular indole production/cell growth in E. coli. Sub-inhibitory concentrations of ampicillin (2 μg/mL) and kanamycin (2 μg/mL) were added at the beginning of culturing in LB medium at 37°C. Each data point was averaged from at least four independent cultures and one standard deviation is shown.
Fig. 3
Fig. 3
Effect of indole on cell growth in the presence of ampicillin. Sub-inhibitory concentration of ampicillin (2 μg/mL) was added at the beginning of culturing E. coli K-12 BW25113 and E. coli K-12 BW25113 ΔtnaA (indole deficient mutant (Lee et al., 2008)) in LB medium at 37°C. Exogenous indole (1 mM) was added to test the effect of indole. Each data point was averaged from four independent cultures and one standard deviation is shown.
Fig. 4
Fig. 4
Effect of indole and ampicillin on cell morphology of E. coli. For SEM analysis, cells were grown in LB medium in the absence of exogenous indole (A), with 1 mM indole (B), with 2 μg/mL ampicillin (C), or with 2 μg/mL ampicillin and 1 mM indole (D). Cells were cultured in LB medium at 37°C for 6.5 h and were directly fixed by adding glutaraldehyde and formaldehyde and filtered with 0.45 μm Nylon filter.
Fig. 5
Fig. 5
Effect of temperature on extracellular indole production/cell growth in E. coli. Cells were cultured in LB medium at 25°C, 37°C, and 50°C. Each data point was averaged from at least four independent cultures and one standard deviation is shown.

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