Photoelectric effects in bacterial chromatophores. Comparison of spectral and direct electrometric methods

Generation of photoelectric potential in chromatophores of Rhodopseudomonas sphaeroides has been measured (i) spectrophotometrically, using electrochromic shift of carotenoid absorption band or (ii) electrometrically, by means of two electrodes separated by a collodion film covered on one side with chromatophores. A 15 ns laser flash was used to induce a single turnover of photosynthetic reaction centers. It was found that results obtained by both methods are similar in (i) direction of electric vector (the chromatophore interior positive) and (ii) redox titration curves (E_m = 10mV). The magnitudes of the photopotential were about 60 and 25 mV, when monitored with spectral and electrometric techniques, respectively. In both cases, the rise times of the photopotentials were faster than time resolution of the techniques used. Decay of the response of carotenoids was found to be slower than that in the collodion film system. The addition of ubiquinone Q₁₀ into the decane solution of asolectin used to impregnate the collodion film led to slowing down of the decay. The carotenoid response decay could be accelerated by FCCP or o-phenanthroline. In the latter case, the shape of the decay curve coincides with decay of the photopotential measured in the collodion film system. It is suggested that decane extracts secondary ubiquinone from chromatophores attached to the collodion film. Such an unfavorable effect can be strongly decreased by added ubiquinone     

Quantitative estimation of poly-3-hydroxybutyric acid in some oligotrophic polyprosthecate bacteria

Quantitative estimation of poly-3-hydroxybutyric acid (PHB) was done in three representative genera of polyprosthecate bacteria:Labrys monachus, Prosthecomicrobium hirschii, Stella vacuolata. The highest PHB content, up to 28% of the dry biomass matter (independent of growth phase), was found inS. vacuolata. Bacteria of generaLabrys andProsthecomicrobium produce 26% and 23% less PHB, respectively, and show a PHB accumulaton dependence on growth phase. The possible reasons of PHB accumulation by oligotrophic polyprosthecate bacteria are discussed.