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journalArticle Phan Hoang C. Wade Scott A. Blackall Linda L. Microbial communities of orange tubercles in accelerated low water corrosion The rapid degradation of marine infrastructure at the low tide level due to accelerated low water corrosion (ALWC) is a problem encountered worldwide. Despite this, there is limited understanding of the microbial communities involved in this process. We obtained samples of the orange-coloured tubercles commonly associated with ALWC from two different types of steel sheet piling, located adjacent to each other but with different levels of localised corrosion, at a seaside harbour. The microbial communities from the outer and inner layers of the orange tubercles, and from adjacent seawater, were studied by pure culture isolation and metabarcoding of the 16S rRNA genes. A collection of 119 bacterial isolates was obtained from one orange tubercle sample, using a range of media in anaerobic and aerobic conditions. The metabarcoding results showed that sulfur and iron oxidisers were more abundant on the outer section of the orange tubercles compared to the inner layers, where Deltaproteobacteria (which includes many sulfate reducers) were more abundant. The microbial communities varied significantly between the inner and outer layers of the orange tubercles and also with the seawater, but overall did not differ significantly between the two steel sheet types. Hence we saw similar microbial communities in orange tubercles present, but different levels of localised corrosion, for two different types of co-located steel sheet piling. Metallurgical analysis found differences in composition, grain size, ferrite-pearlite ratio and the extent of inclusions present between the two steel types investigated. IMPORTANCE The presence of orange tubercles on marine steel pilings is often used as an indication that accelerated low water corrosion is taking place. We studied the microbial communities in attached orange tubercles on two closely located sheet pilings that were of different steel types. The attached orange tubercles were visually similar, but the extent of underlying corrosion on the different steel surfaces were substantially different. No clear difference was found between the microbial communities present on the two different types of sheet piling. However, there were clear differences in the microbial communities in the corrosion layers of tubercles, which were also different to the microbes present in adjacent seawater. The overall results suggest that the presence of orange tubercles, a single measurement of water quality, or the detection of certain general types of microbes (e.g. sulfate reducing bacteria) should not be taken alone as definitive indications of accelerated corrosion. 2020/04/24 en https://aem.asm.org/content/early/2020/04/20/AEM.00610-20 2020-04-29 11:40:55 aem.asm.org Copyright © 2020 American Society for Microbiology.. All Rights Reserved. Publisher: American Society for Microbiology Section: Environmental Microbiology PMID: 32332140 Applied and Environmental Microbiology Appl. Environ. Microbiol. DOI 10.1128/AEM.00610-20 ISSN 0099-2240, 1098-5336