Succession of sulfur-oxidizing bacteria in the microbial community on corroding concrete in sewer systems

Abstract

Microbially induced concrete corrosion (MICC) in sewer systems has been a serious problem for a long time. A better understanding of the succession of microbial community members responsible for the production of sulfuric acid is essential for the efficient control of MICC. In this study, the succession of sulfur-oxidizing bacteria (SOB) in the bacterial community on corroding concrete in a sewer system in situ was investigated over 1 year by culture-independent 16S rRNA gene-based molecular techniques. Results revealed that at least six phylotypes of SOB species were involved in the MICC process, and the predominant SOB species shifted in the following order: Thiothrix sp., Thiobacillus plumbophilus, Thiomonas intermedia, Halothiobacillus neapolitanus, Acidiphilium acidophilum, and Acidithiobacillus thiooxidans. A. thiooxidans, a hyperacidophilic SOB, was the most dominant (accounting for 70% of EUB338-mixed probe-hybridized cells) in the heavily corroded concrete after 1 year. This succession of SOB species could be dependent on the pH of the concrete surface as well as on trophic properties (e.g., autotrophic or mixotrophic) and on the ability of the SOB to utilize different sulfur compounds (e.g., H2S, S0, and S2O3(2-)). In addition, diverse heterotrophic bacterial species (e.g., halo-tolerant, neutrophilic, and acidophilic bacteria) were associated with these SOB. The microbial succession of these microorganisms was involved in the colonization of the concrete and the production of sulfuric acid. Furthermore, the vertical distribution of microbial community members revealed that A. thiooxidans was the most dominant throughout the heavily corroded concrete (gypsum) layer and that A. thiooxidans was most abundant at the highest surface (1.5-mm) layer and decreased logarithmically with depth because of oxygen and H2S transport limitations. This suggested that the production of sulfuric acid by A. thiooxidans occurred mainly on the concrete surface and the sulfuric acid produced penetrated through the corroded concrete layer and reacted with the sound concrete below.

FIG. 1.

Concrete coupons exposed to the sewer atmosphere [H₂S_(g), ca. 30 ppm] for 42 days (A), 102 days (B), and 1 year (C and D), showing the progression of concrete corrosion.

FIG. 2.

Time-dependent changes in surface pH and weight loss of the concrete coupons exposed to the sewer atmosphere (A) and SO₄²⁻ and S⁰ concentrations on the surface of concrete coupons placed in the sewer system (B). In panel A, the line graph refers to pH measurements and the bar graph to weight loss measurements. Error bars represent the standard errors of duplicate measurements.

FIG. 3.

(A) Time-dependent changes of total DAPI-stained (DAPI) cell numbers and EUB338-mixed probe-hybridized (EUB) cell counts on the concrete surface and (B) the relative abundance of EUB338-mixed probe-hybridized cells in relation to total DAPI-stained cells. Error bars represent the standard errors of duplicate measurements.

FIG. 4.

Phylogenetic tree showing the distributions of the OTUs related to sulfur-oxidizing bacteria, which were obtained from 42-day-old (uncorroded, NC), 102-day-old (slightly corroded, SC), and 1-year-old (heavily corroded, HC) samples. The tree was generated by using approximately 1,400 bp of the 16S rRNA genes and the neighbor-joining method. The scale bar represents 2% sequence divergence. The values at the nodes are bootstrap values (500 resampling analysis). The Aquifex pyrophilus sequence served as the outgroup for rooting the tree. The numbers in parentheses indicate the frequencies of appearance of identical clones in the clones analyzed.

FIG. 5.

Time-dependent changes in numerically important SOB cell numbers detected by FISH analysis with SOB species- or genus-specific probes (Table 1). Error bars represent the standard errors of duplicate measurements.

FIG. 6.

(A) Vertical distribution of DAPI-stained total cells, Thio820 probe-hybridized Acidithiobacillus cells, ACD840 probe-hybridized Acidiphilium cells, and LF655 probe-hybridized Leptospirillum cells in the heavily corroded gypsum layer after a 1-year exposure to the sewer atmosphere. (B) Concentration profiles of O₂ and pH in the top 2,000 μm of the heavily corroded gypsum layer that was exposed to the H₂S atmosphere for 1 year. Stable total H₂S concentration profiles could not be determined in this study. The surface of corroded concrete is at a depth of 0 μm. Error bars represent the standard errors of duplicate measurements (A) and of triplicate measurements (B).