Effects of electric field on the photocycle of bacteriorhodopsin

The photoconversion of bacteriorhodopsin and the effects of an applied electric field (5 · 10⁷ V · m^?1) were studied in dry films of purple membranes from Halobacterium halobium. The electric field was found to cause at least two different effects: (1) it blocks in part the formation of the batho-bacteriorhodopsin (K), most probably due to electrically-induced dark transition of some bacteriorhodopsin molecules into the photochemically inactive form; (2) it decreases the rate of the intermediate M decay, the rise time of the M formation being unaffected by electric field. The observed phenomena may suggest a feedback control mechanism for the regulation of the bacteriorhodopsin photocycle in purple membranes.     

On the quantitation of bacteriochlorophyll in chromatophore suspensions from purple bacteria

A direct photometric quantitation of bacteriochlorophyll (BChl) at 375 nm in aqueous chromatophore suspensions from various purple bacteria is described. The assay is rapid and reproducible. It is utilized easily for processing large numbers of samples and is as sensitive as extraction methods usually applied today. Drawbacks of extraction methods, particularly not quantitative extractions, photo- and autooxidation are avoided. There is good linearity up to 20 μg BChl/ml suspension, and no interference by buffers is observed.     

Factors affecting poly-β-hydroxybutyrate accumulation in cyanobacteria and in purple non-sulfur bacteria

Abstract Spirulina maxima and Rhodopseudomonas palustris , which are known to be capable of synthesizing poly-β-hydroxybutyrate (PHB), were grown under different conditions in order to investigate the metabolic significance of PHB synthesis in phototrophic microorganisms. The intracellular concentration of PHB in S. maxima , growing photoautotrophically in batch cultures under either balanced or unbalanced (depletion of nitrogen or phosphorus in the mineral medium) conditions, was below 0.005% of cell dry weight. PHB was synthesized (up to 0.7% of dry weight) only after a prolonged period of N-starvation (although no PHB synthesis occurred when N-starvation was induced by azaserine addition) or when cells, after the exhaustion of intracellular phosphorus reserves, became P-starved. Under the latter condition, the PHB concentration reached a value of 1.2% of cell dry weight, the same figure reached in the presence of the uncoupler carbonylcyanide- m -chlorophenylhydrazone (CCCP). When photosynthetic activity was enhanced by a sudden shift of the culture to higher light intensity or when S. maxima was grown at 18°C, no PHB synthesis was detectable. Under all the photoautotrophic growth conditions tested, glycogen was much more heavily accumulated than PHB. Batch cultures of R. palustris , growing photoheterotrophically on acetate with varying nitrogen sources and regimens of nitrogen supplementation, demonstrated that some competition for reducing equivalents exists between nitrogenase activity and PHB biosynthetic pathway. The results seem to suggest that, in phototrophic bacteria able to synthesize both PHB and glycogen, the polyester acts mainly as a regulator of the intracellular reduction charge.     

Comparative and evolutionary aspects of the photosynthetic electron transfer system of purple bacteria

The cyclic electron transfer system in purple bacteria is composed of the photosynthetic reaction center, the cytochromebc ₁ complex, cytochromec ₂, and ubiquinone. These components share many characteristics with those of photosynthesis and respiration in other organisms. Studies of the cyclic electron transfer system have provided useful insights about the evolution and general mechanisms of membranous energy-conserving systems. The photosynthetic system in purple bacteria may represent a prototype of highly efficient, energy-conserving electron transfer systems in the organisms. Recipient of the Botanical Society Award of Young Scientists, 1992     

Benign Environments do not Explain the Increased Vigour of Non-indigenous Plants: a Cross-continental Transplant Experiment

Invasive plants tend to be taller and produce more biomass in their introduced range than conspecifics growing in their native range. Such observations are usually explained by more 'benign' environments, implying that plastic, phenotypic responses are responsible for increased vigour. We compared the growth of 10 Lythrum salicaria populations from indigenous and non-indigenous distributions in two gardens: one located in Europe (indigenous range), the other in North America (non-indigenous range). Spearman rank correlations of different growth variables were generally significant, suggesting that certain genotypes show increased vigour regardless of growing location. More benign climates or the absence of natural enemies are not sufficient to explain this increased vigour. Plant performance tended to be higher in populations from the introduced range, though few differences were statistically significant. To test alternative hypotheses of 'increased vigour' larger sample sizes will be required which was not attempted in this study.     

Arsenic respiration and detoxification by purple non-sulphur bacteria under anaerobic conditions

Two arsenic-resistant purple non-sulphur bacteria (PNSB), Q3B and Q3C, were isolated (from industrial contaminated site and paddy fields) and identified by SSU rRNA gene sequencing as Rhodospirillum and Rhodospirillaceae species, respectively. Maximum arsenic reduction by these PNSB was observed in anaerobic conditions. Rhodospirillum sp. Q3B showed 74.92% (v/v) arsenic reduction while Rhodospirillaceae sp. Q3C reduced arsenic up to 76.67% (v/v) in anaerobic conditions. Rhodospirillaceae sp. Q3C was found to contain highest carotenoid content up to 5.6 mg·g⁻¹. Under anaerobic conditions, the isolates were able to respire arsenic in the presence of lactate, citrate, and oxalate. Rhodospirillum sp. Q3B and Rhodospirillaceae sp. Q3C were also found to produce hydrogen gas. Such diverse bacteria can be useful tools for bioremediation purposes. These bacteria can be further exploited and optimized to treat wastewater containing arsenic along with bio-hydrogen production.     

Characterisation of the LH2 spectral variants produced by the photosynthetic purple sulphur bacterium Allochromatium vinosum

This study systematically investigated the different types of LH2 produced by Allochromatium (Alc.) vinosum, a photosynthetic purple sulphur bacterium, in response to variations in growth conditions. Three different spectral forms of LH2 were isolated and purified, the B800-820, B800-840 and B800-850 LH2 types, all of which exhibit an unusual split 800 peak in their low temperature absorption spectra. However, it is likely that more forms are also present. Relatively more B800-820 and B800-840 are produced under low light conditions, while relatively more B800-850 is produced under high light conditions. Polypeptide compositions of the three different LH2 types were determined by a combination of HPLC and TOF/MS. The B800-820, B800-840 and B800-850 LH2 types all have a heterogeneous polypeptide composition, containing multiple types of both α and β polypeptides, and differ in their precise polypeptide composition. They all have a mixed carotenoid composition, containing carotenoids of the spirilloxanthin series. In all cases the most abundant carotenoid is rhodopin; however, there is a shift towards carotenoids with a higher conjugation number in LH2 complexes produced under low light conditions. CD spectroscopy, together with the polypeptide analysis, demonstrates that these Alc. vinosum LH2 complexes are more closely related to the LH2 complex from Phs. molischianum than they are to the LH2 complexes from Rps. acidophila.     

Fast electric response signals in the bacteriorhodopsin photocycle

The time behavior of flash-induced charge movements during the first steps in the bacteriorhodopsin photocycle was measured on a suspension of purple membranes oriented by an electric field. The experiments were done in the temperature range 80–278 K. During the formation of the intermediate K, two negative (with respect to the direction of the proton pump) components of the response signal are well resolved with time constants τ₁ < 3 μs and $\text{τ}{}_2\text{? 150 μ}\text{s}$ at 200 K. The distances of the charge displacements responsible for the electric signals are estimated. On the basis of the results the two components are assigned to two steps in the trans-cis isomerization of the retinal. A third negative component appears at higher temperatures which is related by time constant measurements to the K → L transition.     

The biosynthesis of carbamoyl phosphate by Ectothiorhodospira shaposhnikovii and its utilization in carbamoylation reactions

Abstract Carbamoyl phosphate is synthesized by the purple bacterium Ectothiorhodospira shaposhnikovii from CO₂, NH₃ and ATP and is used for enzymatic transfer of the carbamoyl moiety to ornithine. In addition to this reaction nonenzymatic carbamoylation of some amino derivatives occurs, especially at high concentrations of the carbamoyl acceptors and at a temperature of about 45°C. The role of such reactions is discussed.