Quick Discrimination of Heavy Metal Resistant Bacterial Populations Using Infrared Spectroscopy Coupled with Chemometrics

Abstract

Lead and cadmium are frequently encountered heavy metals in industrially polluted areas. Many heavy metal resistant bacterial strains have a high biosorption capacity and thus are good candidates for the removal of toxic metals from the environment. However, as of yet there is no accurate method for discrimination of highly adaptive bacterial strains among the populations present in a given habitat. In this study, we aimed to find distinguishing molecular features of lead and cadmium resistant bacteria using Attenuated Total Reflectance-Fourier Transformed Infrared (ATR-FT-IR) spectroscopy and chemometric approaches. Our results demonstrated that both control and metal exposed E. coli and S. aureus strains could be successfully discriminated from each other using hierarchical cluster and principal component analysis methods. Moreover, we found that lead exposed bacterial strains could be successfully discriminated from cadmium exposed ones with a high heterogeneity value. These clear discriminations can be described by the ability of a bacterium to change its metabolism in terms of the content and structure of cellular macromolecules under heavy metal stress. In our case, cadmium and lead-induced genetic response systems in bacteria caused remarkable alterations in overall cellular metabolism. Bacteria deal with a heavy metal stress by altering nucleic acid methylations and lipid and protein synthesis. Heavy metal burden led to the development of relevant metabolic changes in proteins, lipids, and nucleic acids of the resistant bacteria described in this study. Our approach showed that infrared spectra obtained via ATR-FT-IR spectroscopy coupled with chemometric analysis can be utilized for rapid, low-cost, informative, reliable, and operator-independent discrimination of resistant bacterial populations.

Aspects of silver tolerance in bacteria: infrared spectral changes and epigenetic clues

“…A significant decrease in the band intensities for this band was measured in the Ag-exposed bacteria (Table 1), indicating diminished polysaccharide content [8], in accordance with our previous findings on Co-acclimated bacteria [9]. On the other hand, these results are opposed to those obtained from Pb exposure [8]. It is well known that polysaccharides are sugar polymers in the cell walls of bacteria and found as extracellular polysaccharides (EPSs) [19].…”

“…The changes in the polysaccharides under Ag adaptation were evaluated by calculating the intensity of C─O stretching band located at 1057 cm -1 [8]. A significant decrease in the band intensities for this band was measured in the Ag-exposed bacteria (Table 1), indicating diminished polysaccharide content [8], in accordance with our previous findings on Co-acclimated bacteria [9].…”

“…As can be seen from Table 1, the intensity of this band increased significantly in the Ag-exposed bacteria evidencing elevated lipid content [15]. On the contrary, we found a decrease in lipid amounts in Cd-and Pb-exposed bacteria in our former study [8]. On the contrary, we found a decrease in lipid amounts in Cd-and Pb-exposed bacteria in our former study [8].…”

“…The significant decrease in the intensities of this band for the Ag-exposed bacteria indicates a decreased nucleic acid concentration [8]. The comparison of the intensities of the band due to the C─O stretching of RNA revealed a significant decrease in both Ag-exposed bacteria (Table 1), demonstrating decreased RNA content [9] and supporting our former study dealing with Cd-and Pbexposed bacteria [8]. The comparison of the intensities of the band due to the C─O stretching of RNA revealed a significant decrease in both Ag-exposed bacteria (Table 1), demonstrating decreased RNA content [9] and supporting our former study dealing with Cd-and Pbexposed bacteria [8].…”

“…In our previous work [8], the growth of the same bacteria under inhibitory concentrations of Cd and Pb was evaluated. Ag inhibitory concentrations were determined as 130 μM for E. coli and 94 μM for S. aureus.…”