JOURNAL OF BIOSCIENCE 心ID BIOENGIN皿RING

Vol. 88, No. 3, 300-305. 1999

Isolation of Iron-Oxidizing Bacteria from Corroded Concretes ofSewage Treatment Plants
TERUNOBU MAEDA,1 ATSUNORI NEGISHl,1 HIROMI KOMOT0,2 YUKO OSHIMA,2KAZUO KAMIMURA, 2 AND TSUYOSHI SUGIび ＊T砕ni四l Research Institute, Hazama Corporation, 515-1 Nishimukai, Karima, Tsukuba 305-08221 and Department ofBiological Function and Genetie釦sources Science, Faculty of Agriculture, Okayama Universi机1-1-1Tsushima Naka, Okayama 700-8530,2 Japan
Received 10 March 19勁Accepted 10 June 1 効知Thirty-血strains of iron-oxidizing bacteria weri isolated from corroded concrete s皿1ples obtained at eight
sewage treatment plants in Japan. All of the strains isolated grew autotrophieally in ferrous sulfate (3.0%),
elemental sulfur (1.0%) and FeS (1.0%) media (pH 1.5). Washed intact cells of the 36 isolates had血ivities tooxidize both ferrous iron and elemental sulfur. Strain SNA-5, a representative of the isolated strains, was agram-n喧ative, rod-shaped bacterium (0.5-0.6 x 0.9--1.5µm). The mean G + C content of its DNA was
55.9 mol%. The pH 皿 d temperature optima for growth were 1.5 and 30° C, and the bacterium had a叫vityto
邸similate叱0 2 into the cells when ferrous iron or elemental sulfur w邸 used as a sole source of ene屯y. These
re皿Itssugg邸t that SNA-5 is Thiob叫llus ferrooxid皿s strain. The pHs 皿d numbers of iron-o血izing bacteria
in corroded concrete s皿pl邸 obtained by boring to dept郎of 0-1, 1-3, and 3-5 cm below the concrete surface
werer邸pectively 1.4, 1. 7, and 2.0, and 1.2 x 108, 5 x 1飢皿d 5 x 106 cells/g concrete. The d.屯ree of corrosionin the sample obtained nearest to the surface was more severe than in the deeper s皿1ples. The :findings
indicated that the levels of addiflt'ation and corrosion of the concrete structure corresponded with the numberof iron-oxidizing bacteria in a concrete 暉mple. Sulfuric acid produced by the chemolithoautotrophic sulfur­
oTidiring畑fterimn Thio知illus thiooxidan曲known to induce con匹te corrosion. Since not only T. thiooxi,山msbut also T.ferrooxidans can oxidize reduced sulfur compounds and produce 皿lfuric acid, the results strongly
suggest that T. ferrooxi山rns as well as T. thiooxid血s is involved in concrete corrosion.
[Key words: iron-oxidizing b邸teri皿1, Thiobacill四 ferrooxidans, sulf皿oxidizing bacterium, concrete,corrosion]Parker first presented evidence that concrete structures
are corroded by sulfuric acid produced by the sulfur­
oxidizing bacterium Thiobacillus concretivourus (1-3)
Concrete in its main structure is composed of calciumoxides, hydroxi,des, and carbonates, and these com­pounds can react with sulfuric acid to give calcium sul—fate (gypsum) (4). This resultant calcium loss greatly
diminishes the strength of concrete structures. The bac­terium isolated by Parker was later identified 邸 Thio­
bacillus thiooxidans, and thiob邸illi other than T. thioox­
idans (5, 6), namely Thiobaci/lus neapolitanus, T. inter­medius, .Thiobacillus novellus, and Thiobacillus versutus
have also been isolated from sewer systems and corroded
concrete (7ー 10). The iron-oxidizing bacterium Thiobacil­
lus ferroo豆dans mainly inhabits drainage areas in acidmines and plays a crucial role in the bacterial leachingof sulfide ores (11-15). As well as T. thiooxidans, T. fer­rooxidans is also known to oxidize reduced inorganic sul­
fur compounds and Produce sulfuric acid. The enzvmes

Japan. To our knowledge, there have been no previous
reports on concrete corrosion by microorganisms thathave focussed on iron-oxidizing bacteria.

遍MATERIALS AND METHODS祢Microorg1111isms, media, conditions of cultivation, andisolation procedures
T. ferrooxidans AP19-3 (16, 19)
and 36 strains of iron-oxidizing bacteria isolated fromcorroded concrete samples obtained at eight sewage treat­ment plants in Japan were used throughout this study.
Among the 36 strains, strains SNA-1, SNA-3, and SNA-5
were isolated from samples r邸pectively obtained by boring
0-1, 1-3, and 3-5 cm in depth from the surface of cor­roded concrete at a sewage treatment plant in Saitama
prefecture, and strains SYU-2 and SYU-4 from samples
respectively obtained by boring 0-2 and 2-4 cm into cor­roded concrete obtained at a sewage treatment plant inShizuoka nrefeQfute. Strain OI'P 5-10 was isolated from