Copper susceptibility in Acinetobacter junii BB1A is related to the production of extracellular polymeric substances

Acinetobacter junii BB1A cells, grown in different media, were differentially inhibited in the presence of the copper. The minimum inhibitory concentration of Cu²⁺ was influenced by the nutrient status of the media. The production of extracellular polymeric substances (EPS) was stimulated by the copper present in the growth medium. The nature of the EPS was anionic showing non-Newtonian pseudoplastic behaviour. The thermal behaviour of the EPS was studied by differential scanning calorimetry. The EPS was amorphous in nature with a crystalline index of 0.16. Scanning electron micrographs revealed its porous structure. Cells grown in the presence of quorum sensing inhibitor (QSI: 4-Nitropyridine-N-oxide) did not produce EPS and were found to be more sensitive to Cu²⁺ than cells which produced EPS in the absence of QSI. EPS production in different media in the presence and absence of Cu²⁺ was determined. The production of EPS was the highest in brain heart Infusion medium and the lowest in AB minimal medium. The sorption of Cu²⁺ by EPS extracted from cells grown in non-copper-complexing AB medium was demonstrated by energy dispersive X-ray spectroscopy. A pertinent functional aspect of EPS in providing protection to A. junii in copper stress condition has been revealed.