A systematic apprpach for the selective isolaion of magnetotactic bacteria form marine sediments

摘要

ABSTRACT: Magnetotactic bacteria (MTB) are aquatic prokaryotes; they orient themselves under the earth"s magnetic field by the presence of magnetosomes. The studies on the isolation and identification of MTB are very less, because it lacks any systematic isolation procedure or commercial media. Up to date there is no study on magnetotactic bacteria from Indian coast. In this study, we are reporting for the first time, a magnetotactic spirillum in the Pulicat lagoon, southern coast of India is isolated using a systematic and selective procedure. The sampling site, Pulicat lagoon was chosen on the basis of physicochemical conditions that favours the growth of the MTB. The sediment analysis using FTIR and XRD revealed the presence of magnetite and other minerals such as clinochlore, phlogopite, nontronite and halloysite which are the main sources of iron for the magnetotactic bacteria in the environment. In the current study a new combination of techniques including capillary racetrack purification, oxygen sulphide gradient media and extinction dilution showed faster and easier isolation of magnetotactic spirilla from marine sediments. Based on the 16S rRNA gene sequencing analysis the strain was identified as Magnetospirillum and was designated as Magnetospirillum sp. VITRJS1. The bacteria appeared as spirillum as observed by using bright field microscopy and magnetosomes and inclusion bodies were observed by using TEM. The magnetosomes were extracted from the isolate and the size of magnetosomes was measured as 42nm. The mamE and mamO genes which are essential for magnetosome synthesis was also successfully amplified. Our results indicates that the systematic procedure using sediment analysis and a combination of isolation methods enables the selective and rapid isolation of magnetotactic bacteria from an aquatic sediment sample. Keywords: Magnetotactic bacteria; Magnetospirillum sp. VITRJS1; Magnetosomes; Pulicat Lagoon