Abstract
Although some strains of Leptothrix spp. isolated from aquatic environments have been characterized by culturing them in laboratory conditions, they often show morphological and chemical features distinct from those found in natural environments. To resolve this discrepancy, a novel cultivation method was devised for culturing such strains in natural groundwater. Leptothrix sp. strain OUMS1 was pre-cultured in a medium lacking Fe for 2 days, and then injected into a small dialysis tube bag and immersed in a container with continuously flowing groundwater for 1–3 and 14 days. Microscopic analysis of the initial phase of sheath formation and arbitrary comparisons with medium cultures revealed that in groundwater the surface coat of the sheath comprised much thinner fibrils, and an inner sheath wall that was much thinner and more indistinct compared with medium cultures. These differences were probably attributable to poorer secretion from the cell surface in groundwater conditions. A nutrient-rich medium likely activates cell metabolism and promotes secretion, resulting in a thicker inner sheath wall and thicker outer coat fibrils. Aqueous-phase Fe was deposited on immature sheaths in a similar manner in both cultures. These results indicate that laboratory culture of isolated microbes does not always reflect their characteristics in natural environments.
Highlights
Some bacteria serve as distinct nucleation sites for mineral authigenesis in situ [1]
A small bag made of a dialysis tube containing a small aliquot of OUMS1 suspension was found to swell soon after immersion in a container filled with groundwater (Figure 1a)
This color did not correlate well with growing OUMS1 cells and their associated sheath structures inside the bag because the native microbes present in the groundwater multiplied on the outer surface of the bag
Summary
Some bacteria serve as distinct nucleation sites for mineral authigenesis in situ [1]. Our recent electron microscopic and spectroscopic studies have proved that the sheath comprised an ingenious inorganic/organic hybrid resulting from an interaction between bacterial secretion of exopolymers and deposition of aqueous-phase inorganics such as Fe, phosphorous (P), and silicon (Si) [8,9,10], providing further insight into the structural and spatial associations among the constitutional elements in the sheath of Leptothrix spp Strains of this genus have been successfully isolated and allocated to their taxonomic positions [3,11,12] and several researchers have examined the properties of some of these strains in various culture conditions [13,14,15,16]. Electron microscopy (STEM), STEM-secondary electron imaging (SEI), high-angle annular dark field (HAADF)-STEM, and energy dispersive X-ray (EDX) spectroscopy
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