Electron Transfer in Extremely Halophilic Bacteria

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Environmental stress in the form of high ionic strength has been surmounted by a number of organisms in a number of ways. In general, little is known about electron transfer or coupled energy conservation in any of the extreme halophiles. In preliminary studies, the investigator has found that electron transfer mechanisms observed with proteins from nonhalophilic bacteria must be distinct from the extreme halophiles, as electrostatics appear to play an important role in the elctron transfer proecss. Thus, proteins operating in the periplasmic space in moderate and extreme halophiles must control specificity by the use of factors other than electrostatics. In addition, extreme and moderate halophiles appear to have redox proteins which have generally lower redox potentials, are strongly acidic, and in at least two cases have redox potentials which are ionic strength-dependent at high ionic strengths. Thus it appears that in the course of adaptation to a high ionic strength environment, structural alterations at the molecular level have taken place. It should be emphasized that halotolerant bacteria, those able to live both with and without salt, are not obviously different from fresh-water bacteria. Three halophilic organisms will be studied with this grant. Soluble redox proteins (c-type cytochromes and iron-sulfur proteins) from these bacteria will be characterized in terms of location and the effect of osmoregulators and ionic strength on redox potentials, spectral properties, and thermal denaturation. Data will be analyzed in terms of known structural properties and supplemented by computer modeling utilizing 3-D structures of related proteins. Finally, some basic physiological processes will be studied. It is anticipated that the proposed studies will provide new insights into the molecular properties controlling biological electron transfer, a better understanding of the physiology of halophiles, and an increase in our knowledge of the structural and chemical parameters that control protein stability.