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Sharma, Ravish and Shimada, T. and Mishra, V.K. and Upreti, Suchitra and Sardesai, A.A. (2016) Growth inhibition by external potassium ofEscherichia colilacking PtsN (EIIANtr) is caused by potassium limitation mediated by YcgO. Journal of Bacteriology, 198 (13). pp. 1868-1882. ISSN 0021-9193

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Absence of PtsN, the terminal phospho-acceptor of the phosphotransferase system comprising PtsP-PtsO-PtsN, in E. coli confers a potassium sensitive phenotype (K S) as the external K+ concentration ([K+]e) is increased above 5 mM. A growth inhibitory increase in intracellular K+ content, resulting from hyperactivated Trk mediated K+ uptake is thought to be causal to this KS. We provide evidence that the KS of the ΔptsN mutant is associated with K+ limitation. Accordingly, the moderate KS displayed by the ΔptsN mutant was exacerbated in the absence of the Trk and Kup K+ uptake transporters and was associated with reduced cellular K+ content. Conversely overproduction of multiple K+ uptake proteins suppressed the KS. Expression of PtsN variants bearing the H73A, H73D and the H7 3E substitutions of the phosphorylation site histidine of PtsN, complemented the KS. Absence of the predicted inner membrane protein YcgO (also called CvrA) suppressed the KS which correlated with elevated cellular K+ content in the Δ ptsN mutant but the ΔptsN mutation did not alter YcgO levels. Heterologous overexpression of ycgO also led to a KS that was associated with reduced cellular K+ content, exacerbated by the absence of Trk and Kup and alleviated by overproduction of Kup. Our findings are compatible with a model which postulates that KS in the ΔptsN mutant occurs due to K+ limitation resulting from activation of K+ efflux mediated by YcgO, that may be additionally stimulated by [K+]e, implicating a role for PtsN, possibly its dephosphorylated form as an inhibitor of YcgO activity.

Item Type: Article
Depositing User: Dr P Divakar
Date Deposited: 04 May 2016 04:20
Last Modified: 20 Jul 2016 16:47
URI: http://cdfd.sciencecentral.in/id/eprint/719

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