ISOLATION AND IDENTIFICATION OF ONE CAROTENOID-PRODUCING BACTERIUM

Carotenoids represent one of the most widely distributing and structurally diverse classes of natural pigments. Over 600 different carotenoids have been found in nature and some of them are widely used in foods,feeds,pharmaceuticals and cosmetics. Some microorganisms have the ability to synthesize carotenoids with complex structures. The microorganism could be used to produce carotenoids. One strain OB-2 which generates an orange pigment was isolated from water samples in East Lake,Wuhan,where algae blooms were serious. By visible light spectrum scanning,this pigment was estimated as carotenoids. For confirming the classification of OB-2,morphological,physiological and biochemical characterization were applied and PCR was carried out to measure the gene sequence of 16S rRNA. The 16S rDNA of OB-2 was compared with GenBank and the phylogenetic tree was constructed by the neighbour-joining method with related bacteria. The topology of the phylogenetic tree was evaluated by the bootstrap resampling method with 1000 replicates. Gram stains showed that they are gram-positive rods which were arranged as single cells or gemination in young cultures. The basic physiological and biochemical screening reactions were as follows: 1) Obligately aerobic. Slow and weak oxidative production of acid from glucose. 2)Catalase-positive. Do not form it endospores. Not acid-fast. Colonies on LB media are 1 to 2 mm in diameter within 48 hours at 28℃,and exhibit a orange pigment. An nearly complete 16S rRNA gene sequence of OB-2(GenBank accession number:AY262001) was obtained. Sequence analysis based on 16S rDNA suggested that the bacterium was phylogenetically related to members of the genus Microbacterium and Microbacterium kitamiense was the closest relative species of OB-2 with 99 % sequence similarity. Similar result was clearly showed in the phylogenetic dendrogram. The strain OB-2 was identified as Microbacterium kitamiense.