Abstract:
Purple non-sulfur bacteria (PNSB) are a group of Gram-negative anoxyphototrophic
bacteria. This group is recognized by its capability of growing in diverse environments,
physiological versatility and ecological importance as active participants in the carbon,
nitrogen and sulfur cycles. They draw interest because of their wide range of growth modes
which include photoautotrophic, photoheterotrophic and chemoheterotrophic modes. With
these characters, PNSB have potential applications in bioremediation and anaerobic
treatment in waste treatment processes. PNSB are pigmented with bacteriochlorophyll–a
and carotenoids. The characteristic salmon pink to red color of the PNSB is due to the
Spirilloxanthin series of rhodopsin as the major carotenoid and small amounts of Beta
carotene. Absorption spectra of PNSB have maxima at 378, 461, 488-490, 522-525, 800-
807 and 869-872nm.
The present study was aimed at isolation of PNSB from the Winogradsky column and
identifying them using morphological, cultural and biochemical methods. The Winogradsky
column is a model environment which develops highly diverse groups of microorganisms,
usually in stratification, and it was used in this study for easy isolation of PNSB from
samples of mud.
A Purple non sulfur bacterium was isolated using Glutamate-malate selective medium and
identified as Rhodomicrobium vannielii according to the characters described in the
Bergey’s manual of systematic bacteriology; Volume 3 (Staley et al, 1989). The cells were
motile, Gram negative, ovoid to spherical in shape and did not form intracellular sulfur
globules. When incubated anaerobically under light, the isolate produced a red pigment.
Spectral analysis for chlorophyll and carotenoids was done using a spectrophotometer and
Thin Layer Chromatography (TLC). The presence of bacteriochlorophyll-a and carotenoids
was indicated by the presence of a majority of peak maxima at 363, 476, 774 nm. There
were two spots in the TLC of which the Rf values were 0.40 and 0.85, which indicated the
presence of chlorophylls and carotenoids.
