The concentrations of nitrate and nitrite were determined by a DMS 80 Spectrophotometer
according to the Standard Methods (APHA, 1989). Bacteriochlorophyll
(BChl) a was extracted from the pure culture with
acetone–methanol (7:2). Ten milliliters of the cell suspension were centrifuged
first. The pellet was resuspended in 1 ml of distilled water and 9 ml of solvent
mixture was added. After 5 h at 4°C, the mixture was centrifuged. The absorbance
(OD775) of the supernatant was measured at 775 nm. The BChl a
concentration was calculated using the extinction coefficient o775=75 l
mmol−1
·cm−1 given by Clayton (1963). All measurements were performed in
triplicate.