Abstract
In this study we demonstrate that the demosponge Suberites domuncula harbors a Mn(II)-oxidizing bacterium, a Bacillus strain, termed BAC-SubDo-03. Our studies showed that Mn(II) stimulates bacterial growth and induces sporulation. Moreover, we show that these bacteria immobilize manganese on their cell surface. Comparison of the 16S rDNA sequence allowed the grouping of BAC-SubDo-03 to the Mn-precipitating bacteria. Analysis of the spore cell wall revealed that it contains an Mn(II)-oxidizing enzyme. Co-incubation studies of BAC-SubDo-03 with 100 μM MnCl2 and >1 μM of CuCl2 showed an increase in their Mn(II)-oxidizing capacity. In order to prove that a multicopper oxidase-like enzyme(s) (MCO) exists in the cell wall of the S. domuncula-associated BAC-SubDo-03 Bacillus strain, the gene encoding this enzyme was cloned (mnxG-SubDo-03). Sequence alignment of the deduced MCO protein (MnxG-SubDo-03) revealed that the sponge bacterium clusters together with known Mn(II)-oxidizing bacteria. The expression of the mnxG-SubDo-03 gene is under strong control of extracellular Mn(II). Based on these findings, we assume that BAC-SubDo-03 might serve as a Mn reserve in the sponge providing the animal with the capacity to detoxify Mn in the environment. Applying the in vitro primmorph cell culture system we could demonstrate that sponge cells, that were co-incubated with BAC-SubDo-03 in the presence of Mn(II), show an increased proliferation potential.
Highlights
It is amazing that on the deep-sea floor in depths of around 4,000–6,000 m manganese (Mn) can be deposited in polymetallic nodules despite very low concentrations in the surrounding environment [1]of only approximately 0.2 nmol/kg
We identified for the first time a Bacillus strain of Mn(II)-oxidizing bacteria in the demosponge Suberites domuncula
Mn(II)-oxidizing bacteria were isolated from tissue of S. domuncula during a selection procedure on Mn agar plates in modified K-medium, containing 100 μM MnCl2, as described under
Summary
It is amazing that on the deep-sea floor in depths of around 4,000–6,000 m manganese (Mn) can be deposited in polymetallic nodules despite very low concentrations in the surrounding environment [1]. We identified for the first time a Bacillus strain of Mn(II)-oxidizing bacteria in the demosponge Suberites domuncula. This sponge species is especially suitable for the identification of potential symbiotic microorganisms since it can be kept under controlled laboratory conditions for over five years [18]. On the basis of recently published data [12,13], the mnxG gene coding for the MCO has been identified in the newly discovered S. domuncula-associated bacteria. The expression of this gene was found to depend on the presence of Mn in the culture medium. It was found that sizes and gene expression levels of the primmorphs increased if such cultures were incubated in the presence of Mn(II)
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