Studies of pigments and growth in Chloroflexus aurantiacus, a phototrophic filamentous bacterium
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The chlorophyll pigments of Chloroflexus aurantiacus were separated by column chromatography on powdered sugar and were identified by spectrophotometry in various solvents as BChl a and BChl c (chlorobium chlorophyll 660). The bacteriopheophytins were also prepared and characterized-spectrophotometrically. The identity of the BChl a is tentative because of its anomalous phase test behavior and because of changes in its absorption spectrum observed under different conditions of preparation.
Growth rates of Chloroflexus at 55°C and synthesis of the 2 chlorophylls were compared in cells growing under anaerobic conditions at different light intensities. Growth rates increased with increasing light intensity to a saturation level of about 0.30 doublings/hr at 20 000 lux and above during the second exponential phase of growth. The rate of the first exponential phase continued to increase, at least up to 50 000 lux. The specific content of both chlorophylls decreased with increasing light intensity but to different extents. A linear relationship between specific chlorophyll content and growth rate for either chlorophyll was only observed over a limited range of growth rates. The ratio of BChl c/BChl a decreased with increasing light intensity. The greatest change occurred between 300 and 5000 lux. The differential responses of BChl c and BChl a to light intensity were also demonstrated by shifting highly pigmented cells (grown at low light intensity) to high light intensity. In these cases different rates of synthesis of the 2 pigments followed initial adjustments. Carotenoid synthesis did not decrease with increasing light intensity under anaerobic conditions.
Chlorophyll synthesis was suppressed under fully aerobic conditions in dark-ness and light. In either case the pigments were diluted out by continued cell growth. At least 1 carotenoid pigment, however, was synthesized under aerobic conditions. Other carotenoids characteristic of anaerobic growth were not observed.
The chemoheterotrophic aerobic growth rate at 55°C in darkness (0.14 to 0.22 d/hr) was less than the maximum second phase phototrophic rate under anaerobic conditions (0.30 d/hr). Aerobic growth rate in the light was the same as in darkness if chlorophylls were lacking, but was enhanced if these pigments were still present. The oxygen consumption rate was partially suppressed in the light only when chlorophylls were present in the cells.
A light-minus-dark diffrence spectrum revealed the presence of a light-induced reversible decrease in absorbance of BChl a with a maximum effect at 860 nm, tentatively identifying a reaction center complex.
Key wordsChloroflexus Thermophilic Photosynthetic Bacterium Bacteriochlorophyll Pigment Regulation Respiration in Light Carotenoids
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