[Biological characteristics and phylogenetic analysis of a denitrifying photosynthetic bacterium]

Abstract

Objective: Nitrite accumulation in aquaculture water is toxic to reared animals. One of the solutions to this problem is to apply denitrifying bacteria. This paper is intended to get a strain of phototrophic bacteria for efficient removal of nitrite from aquaculture water.

Methods: We used soft agar to isolate and purify phototrophic bacteria. We investigated biological characteristics of the isolate by means of light and electronic observations, physical and chemical tests. We analyzed its phylogenetical position based on the sequences of 16S rDNA and the gene that codes for photosynthetic reaction center subunit M (pufM).

Results: A photosynthetic bacterial strain, named wps, showing high removal efficiency of nitrite, was isolated from the freshwater ponds. Cells were Gram-negative, rod-shaped, slightly curved, 0.4 - 0.6 x 1.5 - 4.0 microm, motile by means of polar multiple flagella. Intracellular membranes were of the lamellar type. It grew under facultative anaerobic conditions in the light with bacteriochlorophyll a and carotenoid of sppirilloxanthin series as photosynthetic pigment. The optimum growth was obtained at pH 5.5 - 8.5, in a range of 0 - 2% salinity and at 25 - 38 degrees C. The similarity of 16S rDNA between strain wps and Rhodopseudomonas palustris was 98.9% and 94.9% for pufM gene. However, there are significant differences between them in the morphological and physiological characteristics, i. e. grew at pH 5.5; no growth photoautotrophicaly with sodium hydrogen carbonate; could not utilize citrate or formate as only carbon source; required thiamine hydrochloride and calcium pantothenate as growth factors.

Conclusion: Strain wps may represent a novel species in genus Rhodopseudomonas and possibly find its application in the bioremediation of polluted aquaculture water.