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Applied and Environmental Microbiology, April 2007, p. 2451-2457, Vol. 73, No. 8
0099-2240/07/$08.00+0     doi:10.1128/AEM.02899-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Persistence and Decontamination of Bacillus atrophaeus subsp. globigii Spores on Corroded Iron in a Model Drinking Water System

Department of Civil and Environmental Engineering, 765 Baldwin Hall, University of Cincinnati, Cincinnati, Ohio 45221,¹ National Homeland Security Research Center, Water Infrastructure Protection Division, U.S. Environmental Protection Agency (MS 163), Cincinnati, Ohio 45268²²

Received 14 December 2006/ Accepted 6 February 2007

Persistence of Bacillus atrophaeus subsp. globigii spores on corroded iron coupons in drinking water was studied using a biofilm annular reactor. Spores were inoculated at 10⁶ CFU/ml in the dechlorinated reactor bulk water. The dechlorination allowed for observation of the effects of hydraulic shear and biofilm sloughing on persistence. Approximately 50% of the spores initially adhered to the corroded iron surface were not detected after 1 month. Addition of a stable 10 mg/liter free chlorine residual after 1 month led to a 2-log₁₀ reduction of adhered B. atrophaeus subsp. globigii, but levels on the coupons quickly stabilized thereafter. Increasing the free chlorine concentration to 25 or 70 mg/liter had no additional effect on inactivation. B. atrophaeus subsp. globigii spores injected in the presence of a typical distribution system chlorine residual (0.75 mg/liter) resulted in a steady reduction of adhered B. atrophaeus subsp. globigii over 1 month, but levels on the coupons eventually stabilized. Adding elevated chlorine levels (10, 25, and 70 mg/liter) after 1 month had no effect on the rate of inactivation. Decontamination with elevated free chlorine levels immediately after spore injection resulted in a 3-log₁₀ reduction within 2 weeks, but the rate of inactivation leveled off afterward. This indicates that free chlorine did not reach portions of the corroded iron surface where B. atrophaeus subsp. globigii spores had adhered. B. atrophaeus subsp. globigii spores are capable of persisting for an extended time in the presence of high levels of free chlorine.

Published ahead of print on 16 February 2007.

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