Annual Variation, Environmental Adaptation And Culture Of Magnetotactic Bacteria From The Intertidal Zone Of Lake Yuehu, Rongcheng

Lake Yuehu is a shallow coastal lagoon located on the east side of Shandong Peninsula, China. Large numbers of magnetotactic bacteria(MTB) are found from the sediment of intertidal zone in the northern part of Lake Yuehu, including two morphotypes(spherical and ellipsoidal) of multicellular magnetotactic prokaryotes(MMPs). Two sites, marked as site A(in the area where a rivulet flows past) and site B(on the edge of the area where a rivulet flows past), were chosen according to their different type dominating at each site. Here their temporal distributions and their relationships with biogeochemical parameters were studied. Moreover, two novel marine magnetococci were cultured by use of modified media of other magnetotactic bacteria.The sample sites are located in low tide region. Samples were collected from sites A and B at approximately two-week intervals during ebb tides from September 2012 to December 2013.The variation in biogeochemical parameters was more pronounced at site A.Although two types of MMPs coexisted at both sites, their numbers were different; at most times spherical MMPs dominated at site A, while ellipsoidal MMPs dominated at site B. Geochemical analysis revealed that the environmental conditions at site A varied more than at site B. Compared with the widely distributed spherical MMPs,ellipsoidal MMPs seemed to prefer more stable habitats.The abundance of MMPs was high in summer and autumn, but low in winter andspring. Furthermore, the peaks in the numbers of the two types of MMPs were sequential, with the highest concentration of the spherical MMPs occurring prior to that of the ellipsoidal MMPs. This may be related to different optimal growth temperatures for the two types. Spherical MMPs prefer relatively higher temperatures than ellipsoidal MMPs.Salinity, organic matter, sulfur, sulfate et al. may regulate the variation in abundance of spherical MMPs, while phosphate, silicate et al. may influence the abundance of ellipsoidal MMPs.Two novel marine magnetococci, RO-1 and RO-2, which were from intertidal zone of Lake Yuehu were cultured. The concentration of these cocci can reach 106 ind./m L after 7 days’ culturation.The cells of strain RO-1 are roughly spherical, with a size of 1.91 ± 0.30 μm × 2.28± 0.44 μm. Magnetosomes arranged in a disorganized cluster and crystals are prismatic magnetite. Each cell had 1-2 flagellar bundles on the long hemisphere. We observed that RO-1 showed a helical trajectory and the average velocity of was 58.8 ±14.9 μm/s.The cells of strain RO-2 are roughly spherical, with a size of 1.17 ± 0.13 μm × 1.48± 0.17 μm. Magnetosomes arranged in one chain(occasionally 2 chains) and crystals are prismatic magnetite. Each cell had 1-2 flagella, which were speculated to be within bundles, on the long hemisphere. We observed that RO-1 showed a helical trajectory and the average velocity of was 163.4 ± 61.8 μm/s.Phylogenetic analysis revealed that 16 S r DNA gene sequences of strain RO-1showed a maximum sequence identity with uncultured bacterium clone XCQD60(KM083512)(96.7%). The sequence of strain RO-2 showed a maximum sequence identity with uncultured Magnetococcus sp. clone MRC-2(KJ591588)(98.0%), and was 96.9% and 93.4% identical to MC-1 and MO-1, respectively. Two strains both belonged to the Alphaproteobacteria and were novel cultured magnetotactic bacteria.