Heavy metal-induced structural and functional changes in clinical and environmental acinetobacter isolates


Thesis Type: Doctorate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Arts and Sciences, Department of Biology, Turkey

Approval Date: 2015

Student: TUĞBA ÖZAKTAŞ

Supervisor: AYŞE GÜL GÖZEN

Abstract:

Heavy metal pollution is a threat resulting from increased anthropogenic activities. Cadmium (Cd), lead (Pb) and silver (Ag) are among the heavily used metals in different industrial areas. The accumulation of these hazardous substances in nature affects all organisms including human. Bacteria can tolerate these toxic heavy metals up to a degree by their intrinsic resistance mechanisms. Heavy metal resistance factors generally assist the spread of resistance to other toxic substances and antibiotics. Acinetobacter species are widely distributed opportunistic pathogens in nature. For assessing the molecular patterns of resistance as well as tolerance of Acinetobacter to heavy metals, an environmental and a clinical isolates were subjected to sub-lethal concentrations of Cd, Pb, and Ag. Extent of molecular changes was measured with ATR-FTIR spectroscopy by using alive intact bacterial cells. There were remarkable differences in molecular changes which manifest themselves as apparent resistance and tolerance strategies. These different strategies then lead to differences in physiologies between the isolates originating from two very different environments. This study showed that Pb was the most influential heavy metal on the cellular molecules; in turn it was the most tolerated one. Especially in environmental strain, Pb and Ag induced the extracellular polysaccharide (EPS) synthesis. Furthermore, one of the noteworthy results of this study is that Pb, in environmental strain, caused formation of multiple strand polyribonucleotide aggregations. Interestingly, membrane dynamics were shaped by Cd and Pb in environmental isolate. In contrast clinical isolate did not exhibit measurable change in membrane dynamics. This study gave evidence on the adaptation to specific environments, by modulating the physiology of a bacterium arising from operating with different strategies. Measurable molecular changes than are attributable to the epigenetic potentials of bacteria which provides selections for modulation.