Correlation between the respiration-driven Na+ pump and Na+-dependent amino acid transport in moderately halophilic bacteria

Abstract

The effect of Na+ on amino acid uptake by moderately halophilic bacteria was examined using a-aminoisobutyric acid (AIB) as a nonmetabolizable amino acid analogue. Of the eight moderate halophiles investigated, the six Gram-negative bacteria that have a respiration-driven Na+ pump specifically required Na+ for AIB uptake. On the other hand, the two Gram-positive bacteria that have no respiration-driven Na+ pump showed no requirement for Na+ for AIB uptake. Thus, the mode of energy coupling to amino acid transport was quite different between the Gram-negative and Gram-positive moderate halophiles tested : the former, but not the latter, utilized Na+ circulation for the active uptake of AIB.

Halophilic Microorganisms and their Environments

“…Two Grampositive bacteria that lack a respiration-driven pump (Marinococcus halophilns, "Micrococcus varians subsp. halophilus") do not require for AIB uptake (Unemoto et al, 1993). NaCl causes a 2-3 fold stimulation of the transport activity of proline in Chromohalobacter israelensis.…”

The Conformational Changes Induced by Ubiquinone Binding in the Na+-pumping NADH:Ubiquinone Oxidoreductase (Na+-NQR) Are Kinetically Controlled by Conserved Glycines 140 and 141 of the NqrB Subunit

“…Na ϩ -pumping NADH:ubiquinone oxidoreductase (Na ϩ -NQR) 4 is a respiratory enzyme found in marine and pathogenic bacteria such as Haemophilus influenzae and Vibrio cholerae (1)(2)(3). Na ϩ -NQR obtains energy by oxidizing NADH and reducing ubiquinone, which allows it to maintain a sodium gradient across the inner bacterial membrane.…”

Riboflavin is a component of the Na + -pumping NADH–quinone oxidoreductase from Vibrio cholerae

“…This is the only known case in which the redox reaction is coupled directly to pumping sodium ions across the cell membrane (2). The electrochemical sodium gradient generated by Na ϩ -NQR is a source of energy for cellular functions such as driving the bacterial flagellum and transporting nutrients into the cell (3,4). Na ϩ -NQR is the entry point for electrons into the respiratory chain of a number of marine and pathogenic bacteria (5-7).…”