Combined Approach for Characterization of Uncultivated Magnetotactic Bacteria from Various Aquatic Environments

Abstract

Both magnetic collection and "race track" purification techniques were highly effective for selective enrichment of magnetotactic bacteria (MTB) from complex communities, as suggested by amplified ribosomal DNA restriction analysis and denaturing gradient gel electrophoresis combined with sequence analysis of 16S rRNA genes. Using these purification methods, the occurrence and diversity of MTB in microcosms from various marine and freshwater environments were assayed by using a combined microscopic, molecular, and cultivation approach. Most microcosms were dominated by magnetotactic cocci. Consistently, the majority of retrieved 16S RNA sequences were affiliated with a distinct cluster in the Alphaproteobacteria. Within this lineage the levels of sequence divergence were <1 to 11%, indicating genus-level diversity between magnetotactic cocci from various microcosms, as well as between MTB from different stages of succession of the same microcosms. The community composition in microscosms underwent drastic succession during incubation, and significant heterogeneities were observed between microcosms from the same environmental sources. A novel magnetotactic rod (MHB-1) was detected in a sediment sample from a lake in northern Germany by fluorescence in situ hybridization. MHB-1 falls into the Nitrospira phylum, displaying 91% 16S rRNA sequence similarity to "Magnetobacterium bavaricum." In extensive cultivation attempts, we failed to isolate MHB-1, as well as most other MTB present in our samples. However, although magnetotactic spirilla were not frequently observed in the enrichments, 10 novel isolates of the genus Magnetospirillum which had not routinely been isolated in pure culture before were obtained.Magnetotactic bacteria (MTB) are a heterogeneous group of aquatic microorganisms which share the ability to orient themselves along magnetic field lines. Magnetic orientation is due to the presence of magnetosomes, which are intracellular membrane-bound crystals of magnetic iron mineral which consist of magnetite or greigite (3,28,29). Diverse MTB, including cocci, spirilla, rods, vibrios, and multicellular aggregates, have been found in different aquatic habitats (5,7,17). Because of their high abundance and their remarkable potential to accumulate and precipitate iron minerals, MTB are assumed to have great impact in the biogeochemical cycling in natural sediments, which, however, has remained poorly understood. Most cultivated and uncultivated MTB have been affiliated with the Alphaproteobacteria. Moreover, the magnetotactic sulfate-reducing bacterium Desulfovibrio magneticus (14) and a magnetotactic, many-celled prokaryote (9) belong to the Deltaproteobacteria, while a giant magnetotactic rod, tentatively named "Magnetobacterium bavaricum," is affiliated with the Nitrospira phylum (34). Recently, a greigite-producing rod belonging to the ␥-Proteobacteria was identified (32). The phylogenetic and morphological diversity of MTB is matched by notable variation in the shapes, organizations, and numbers of magne...

Newly Isolated but Uncultivated Magnetotactic Bacterium of the Phylum Nitrospirae from Beijing, China

“…For example, the average size of MWB-1 cells is smaller than that of LO-1 cells (2.8 by 2.4 m for MWB-1 versus 3.5 by 2.7 m for LO-1), but the average number of magnetosomes and the number of chain bun- MTB in the phylum Nitrospirae were originally described as comprising only "Ca. Magnetobacterium bavaricum" (49) but have recently been recognized to contain bacterial species showing a broad range of morphological properties and with high phylogenetic diversity (10,25,27,30,31). However, no thorough phylogenetic analysis of the Nitrospirae MTB considering all known sequences has been conducted yet.…”

Ecology, Diversity, and Evolution of Magnetotactic Bacteria

“…Magnetobacterium bavaricum" is the most studied and was first discovered in sediment samples from Lake Chiemsee and Lake Ammersee in southern Germany (143,144). Another magnetotactic member of the Nitrospirae, designated strain MHB-1, is a small rod-shaped bacterium collected from sediment of the Waller See, Germany (145). Recently, two new Nitrospirae have been described: a moderately thermophilic species tentatively named "Ca.…”

“…Strain MHB-1 is a small, rod-shaped bacterium collected from sediment of the Waller See, Germany (145). This organism is a slow-moving, rod-shaped bacterium that contains a single bundle of multiple chains of magnetite magnetosomes whose crystals are also bullet shaped.…”

Formation of magnetite by bacteria and its application

“…The cell contained up to a 1000 bullet-shaped BacMPs. Recently, a similar magnetotactic rod termed MHB-1 was identified and revealed to have 91% sequence similarity with M. bavaricum, based on 16S rDNA analysis (Flies et al 2005).…”