Respiratory electron transport and light-induced energy transduction in membranes from the aerobic photosynthetic bacterium Roseobacter denitrificans

Candela, M Zaccherini, E Zannoni, D

M. Candela et al., Respiratory electron transport and light-induced energy transduction in membranes from the aerobic photosynthetic bacterium Roseobacter denitrificans, ARCH MICROB, 175(3), 2001, pp. 168-177

53

INGLESE

Article

Microbiology

ARCHIVES OF MICROBIOLOGY

0302-8933 → ACNP

175

3

2001

168 - 177

ISI

0302-8933(200103)175:3<168:RETALE>2.0.ZU;2-G

Membrane fragments isolated from the aerobic phototrophic bacterium Roseoba cter denitrificans were examined. Ninety-five percent of the total NADH-dep endent oxidative activity was inhibited either by antimycin A or myxothiazo l, two specific inhibitors of the cytochrome hc, complex, which indicates t hat the respiratory electron transport chain is linear. In agreement with t his finding, light-induced oxygen uptake, an electron transport activity ca talyzed by the ,,alternative quinol oxidase pathway" in membranes of severa l facultative phototrophic species, was barely detectable in membranes of R sb. denitrificans. Redox titrations at 561-575 nm, 552-540 nm, and 602-630 nm indicated the presence of three h-type cytochromes (E-m.7 of +244+/-8, 24+/-3, -163+/-11 mV), four c-type cytochromes (E-m.7 of +280+/-10, +210+/- 5, +125+/-8, and 20+/-3 mV) and two a-type cytochromes (E-m.7 of +335+/-15, +218+/-18 mV). The latter two a-type hemes were shown to be involved in cy tochrome c oxidase activity, which was inhibited by both cyanide (I-50=2 mu M) and azide (I-50=1 mM), while a soluble cytochrome c (c(551), E-m.7=+217/-2 mV) was shown to be the physiological electron carrier connecting the b c(1) complex to the cytochrome c oxidase. A comparison of the ATP synthesis generated by continuous light in membranes of Rsb. denitrificans and Rhodo bacter capsulatus showed that in both bacterial species photophosphorylatio n requires a membrane redox poise at the equilibrium (E(h)greater than or e qual to +80 less than or equal to +140 mV), close to the oxidation-reductio n potential of the ubiquinone pool. These data, taken together, suggest tha t, although the photosynthetic apparatus of Rsb. denitrificans is functiona lly similar to that of typical anoxygenic phototrophs, e.g. Rba. capsulatus , the in vivo requirement of a suitable redox state at the ubiquinone pool level restricts the growth capacity of Rsb. denitrificans to oxic condition s.