Unusual Bacterially mediated manganese-based structures within biofilms from urban streams.

Abstract

The objectives of this study were to describe the occurrence and nature of unusual brown “doughnut”-shaped microbial structures present within the biofilms of several urban streams in Auckland, New Zealand, and the bacteria responsible for their formation. These structures, termed anelli, were observed with light and scanning electron microscopy to be shallow conical microcolonies consisting of a ring, enriched in manganese and iron, surrounding a central pore. Bacteria were observed to reside within the pores, although anelli seen within biofilms were frequently vacant structures. A manganese depositing, anellus-forming bacterium (JOSHI_001) was isolated on solid media, and analysis of 16S rRNA gene sequences revealed this bacterium to belong to the order Burkholderiales within the class β-proteobacteria, closely related to the manganese-depositing genus Leptothrix. The presence of anelli within biofilms was found to require Mn(II), however, elevated levels of this element within stream water did not necessarily result in growth of anelli. Anelli were only dominant structures within biofilms from those stream sites subjected to a high level of anthropogenic impact, suggesting that Mn(II) may not be the only factor influencing competitive capability. Investigation of additional streams within the Auckland region, influenced by a range of different types of anthropogenic impact is ongoing. Molecular analysis indicated that although anelli were structurally dominant, the β-proteobacteria comprised only a minor component of the bacterial community present within the biofilms. JOSHI_001 may have a significant impact on geochemical cycling and stream ecology within streams subjected to high levels of anthropogenic impact.