Iron Bacteria in Drinking-Water Distribution Systems: Elemental Analysis of Gallionella Stalks, Using X-Ray Energy-Dispersive Microanalysis

Abstract

“Iron” bacteria belonging to the genus Gallionella were observed by scanning electron microscopy in water samples and attached to pipe surfaces in a Southern California drinking-water distribution system. The cells were recognized by their characteristic elongated helical stalks composed of numerous intertwined microfibrils. Many of the stalks were partially coated with insoluble ferric salt deposits. Stalks recovered directly from water samples were analyzed for their elemental composition by using X-ray energy-dispersive microanalysis. Silicon, aluminum, calcium, and iron were the predominant elements present in the stalks. Smaller quantities of the elements phosphorous, sulfur, chlorine, copper, and zinc were also detected. Manganese, though present in measurable quantities in the water supply, was not detected in the stalks, suggesting that this organism is unable to utilize this element as an electron donor. This represents the first such analysis of Gallionella stalks recovered from environmental samples without prior subculturing in artificial laboratory media.