Remedial Treatment of Corroded Iron Objects by Environmental Aeromonas Isolates

Abstract

Microbiology can greatly help in the quest for a sustainable solution to the problem of iron corrosion, which causes important economic losses in a wide range of fields, including the protection of cultural heritage and building materials. Using bacteria to transform reactive and unstable corrosion products into more-stable compounds represents a promising approach. The overall aim of this study was to develop a method for the conservation and restoration of corroded iron items, starting from the isolation of iron-reducing bacteria from natural environments. This resulted in the identification of a suitable candidate (Aeromonas sp. strain CU5) that mediates the formation of desirable minerals at the surfaces of the objects. This led to the proof of concept of an application method on real objects.

Investigation of Biogenic Passivating Layers on Corroded Iron

“…The development of new and ecologically friendly strategies to protect outdoor iron surfaces has a clear economical, as well as ecological, interest. We demonstrated the potential of bacteria as an alternative for the development of innovative and green methods to protect iron artifacts from detrimental corrosion [24][25][26][27][28]. Here, the obtained results allow us to better understand how reactive corrosion layers are converted into biogenic iron phosphates with Desulfitobacterium hafniense.…”

“…As part of our research topic, we investigated the potential of microbes for the stabilization of already corroded iron (archaeological objects and outdoor surfaces) by converting part of the reactive corrosion layer into more stable biogenic minerals ( Figure 1). In particular, we studied different bacterial species, Shewanella loihica, Desulfitobacterium hafniense and Aeromonas spp., for their ability to produce biogenic iron minerals on corroded steel coupons [24][25][26][27][28]. Hence, vivianite and siderite were produced by S. loihica on costal-exposed coupons, while D. hafniense and Aeromonas spp.…”

“…Hence, vivianite and siderite were produced by S. loihica on costal-exposed coupons, while D. hafniense and Aeromonas spp. induced the formation of vivianite and siderite on urban-exposed coupons [26][27][28]. In order to better understand the biomineralization process involved, corroded coupons exposed in an urban environment and treated with D. hafniense have been investigated through the present stratigraphic study.…”

The Bad and the Good—Microorganisms in Cultural Heritage Environments—An Update on Biodeterioration and Biotreatment Approaches

“…Nevertheless, it should be noted that microorganisms often shift between the dormant and active state, depending on the environmental conditions, thus, when carrying out RNA-based analyses, sampling should be conducted multiple times, to prevent time-point bias of complex microbial communities [ 50 , 51 ]. RNA-based research is still rarely performed in cultural heritage microbiology, but there are already some interesting examples of total bacterial transcriptome analyses associated with historic artworks [ 52 ]. It is important to mention that one of the limitations of metatranscriptomic analyses is the lack of well-developed databases, but this may be overcome if metagenome-guided research is performed in parallel.…”

“…Analyses of microorganisms associated with biodeterioration or biotreatment processes are more meaningful if auxiliary techniques, which visualize structural modifications or chemical changes, are applied. It has already been shown, that for complex multi-component analyses several commonly acknowledged techniques may be combined, e.g.,: (i) XRF, XRD, SEM, FM, isotope analyses, coupled with cultivation experiments on Reasoner’s 2A agar and 16S rDNA analyses (Applied Biosystems platform) [ 71 ]; (ii) SEM, RS, FTIR, together with cultivation experiments on Mueller–Hinton medium and 16S rDNA analyses (Applied Biosystems platform) [ 72 ]; (iii) XRD, RS, FTIR, SEM-EDS, confocal microscopy, accompanied with transcriptomic sequencing (Illumina) and shotgun sequencing (PacBio) [ 52 ].…”