Remedial Treatment of Corroded Iron Objects by Environmental Aeromonas Isolates

Wafa M. Kooli; Thomas Junier; Migun Shakya; Mathilde Monachon; Karen W. Davenport; Kaushik Vaideeswaran; Alexandre Vernudachi; Ivan Marozau; Teddy Monrouzeau; Cheryl D. Gleasner; Kim McMurry; Reto Lienhard; Lucien Rufener; Jean-Luc Perret; Olha Sereda; Patrick S. Chain; Edith Joseph; Pilar Junier

摘要

Using bacteria to transform reactive corrosion products into stable compounds represents an alternative to traditional methods employed in iron conservation. Two environmental Aeromonas strains (CA23 and CU5) were used to transform ferric iron corrosion products (goethite and lepidocrocite) into stable ferrous iron-bearing minerals (vivianite and siderite). A genomic and transcriptomic approach was used to analyze the metabolic traits of these strains and to evaluate their pathogenic potential. Although genes involved in solid-phase iron reduction were identified, key genes present in other environmental iron-reducing species are missing from the genome of CU5. Several pathogenicity factors were identified in the genomes of both strains, but none of these was expressed under iron reduction conditions. Additional in vivo tests showed hemolytic and cytotoxic activities for strain CA23 but not for strain CU5. Both strains were easily inactivated using ethanol and heat. Nonetheless, given a lesser potential for a pathogenic lifestyle, CU5 is the most promising candidate for the development of a bio-based iron conservation method stabilizing iron corrosion. Based on all the results, a prototype treatment was established using archaeological items. On those, the conversion of reactive corrosion products and the formation of a homogenous layer of biogenic iron minerals were achieved. This study shows how naturally occurring microorganisms and their metabolic capabilities can be used to develop bio-inspired solutions to the problem of metal corrosion.IMPORTANCE 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. KEYWORDS: Aeromonas , artifacts, corrosion, iron, reduction, vivianiteINTRODUCTIONIron corrosion represents a major problem in man-made ecosystems and causes large economic losses in fields as diverse as water supply, food industries, transport, and cultural heritage (1). While the first three fields are obviously of worldwide importance, the same is the case for the latter, as cultural heritage is a driver of tourism and sustainable development (2). The damage generated by uncontrolled corrosion of archeological objects is a clear example of the negative impact of iron corrosion. Reactive iron oxides and oxyhydroxides are the principal unstable iron corrosion products reported for these objects. Due to their molar volume (higher than that of native iron or iron alloys), these corrosion products generate cracks and irreversible damage of the objects if no intervention occurs (3).In nature, the phenomenon of iron corrosion is an essential part of the biogeochemical cycling of iron. While aerobic corrosion is considered to be primarily a chemical process, anaerobic corrosion is often related to oxidative and/or reductive bacterial activity (1). Iron is a redox-sensitive element. It oxidizes easily in the presence of oxygen to form insoluble Fe(III) oxides. Iron oxides accumulate in sediments and soils (4), where iron can be remobilized through biotic and abiotic reactions (5, 6). Some bacteria are able to catalyze transformations of iron minerals under oxic and anoxic conditions (4). These bacterial metabolisms can be exploited to transform reactive corrosion products (e.g., lepidocrocite) into stable compounds with low molar volumes (7). This represents a promising biotechnological approach to remediate the problem of iron corrosion.In two recent studies (8, 9), the feasibility of a biological treatment using bacteria to remediate iron corrosion has been demonstrated. The strategy consists of the reduction of reactive Fe(III) oxides and oxyhydroxides and the formation of biogenic minerals under anaerobic conditions. Initially, a strict anaerobe ( Desulfitobacterium hafniense ) was used to reduce reactive corrosion products during anaerobic growth. Although reductive dissolution was observed, this approach resulted in the formation of undesirable products. Indeed, in addition to bacterial iron reduction, abiotic reduction caused by the reductant in the medium also occurred and resulted in the formation of sulfur-containing Fe(II) minerals. In addition, the handling of a strict anaerobe and the medium used for reduction were not particularly suitable for application

机译：使用细菌将反应性腐蚀产物转化为稳定的化合物代表了铁保护中使用的传统方法的替代方法。使用两种环境气单胞菌菌株（CA23和CU5）将三价铁腐蚀产物（针铁矿和纤铁矿）转变为稳定的含铁铁矿物（堇青石和菱铁矿）。基因组和转录组学方法用于分析这些菌株的代谢特性并评估其致病潜力。尽管已鉴定出涉及固相铁还原的基因，但CU5基因组中却缺少其他环境中的铁还原物种中存在的关键基因。在两个菌株的基因组中都鉴定出了几种致病性因子，但在铁还原条件下均未表达。其他体内测试显示，CA23菌株具有溶血和细胞毒活性，而CU5则没有。两种菌株都可以使用乙醇和热轻松灭活。但是，由于致病性生活方式的潜力较小，CU5是开发稳定铁腐蚀的基于生物的铁保护方法的最有希望的候选者。根据所有结果，使用考古物品建立了原型处理方法。在这些材料上，实现了反应性腐蚀产物的转化和生物铁矿物均质层的形成。这项研究表明如何利用天然存在的微生物及其代谢能力来开发针对金属腐蚀问题的以生物为灵感的解决方案。重要提示微生物学可以极大地帮助寻求铁腐蚀问题的可持续解决方案，这导致了重要的经济意义。在许多领域的损失，包括文化遗产和建筑材料的保护。使用细菌将反应性和不稳定的腐蚀产物转化为更稳定的化合物代表了一种有前途的方法。这项研究的总体目标是从隔离自然环境中的还原铁细菌开始，开发一种保护和修复腐蚀的铁物品的方法。这导致鉴定出合适的候选物（气单胞菌菌株CU5），该候选物介导物体表面上所需矿物的形成。这导致在实物上应用方法的概念证明。关键词：气单胞菌，人工制品，腐蚀，铁，还原，维维石引言铁腐蚀是人造生态系统中的一个主要问题，并在供水，食品工业，交通运输和文化遗产等众多领域造成了巨大的经济损失（1）。尽管前三个领域显然具有世界范围的重要性，但后者同样如此，因为文化遗产是旅游业和可持续发展的驱动力（2）。考古对象不受控制的腐蚀所产生的损坏是铁腐蚀负面影响的一个明显例子。对于这些目的，反应性氧化铁和羟基氧化铁是主要的不稳定铁腐蚀产物。由于它们的摩尔体积（比天然铁或铁合金的摩尔体积大），如果不进行干预，这些腐蚀产物会产生裂纹和物体不可逆转的损坏（3）。自然，铁腐蚀现象是腐蚀的重要部分。铁的生物地球化学循环。尽管好氧腐蚀被认为是主要的化学过程，但厌氧腐蚀通常与氧化和/或还原细菌活性有关（1）。铁是对氧化还原敏感的元素。它在氧气存在下容易氧化，形成不溶的Fe（III）氧化物。氧化铁积聚在沉积物和土壤中（4），在那里铁可以通过生物和非生物反应而被迁移（5、6）。一些细菌能够在有氧和无氧条件下催化铁矿物质的转化（4）。可以利用这些细菌的新陈代谢将反应性腐蚀产物（例如锂铁云母）转变为低摩尔体积的稳定化合物（7）。这代表了解决铁腐蚀问题的一种有前途的生物技术方法。在两项最近的研究（8、9）中，已经证明了使用细菌进行生物处理以修复铁腐蚀的可行性。该策略包括还原反应性Fe（III）氧化物和羟基氧化物以及在厌氧条件下形成生物矿物。最初，使用严格的厌氧菌（哈弗脱硫杆菌）来减少厌氧生长过程中的反应性腐蚀产物。尽管观察到还原溶解，该方法导致形成不希望的产物。确实，除了细菌铁的还原外，还发生了由培养基中还原剂引起的非生物还原，并导致了含硫的Fe（II）矿物的形成。另外，严格厌氧菌的处理和用于还原的培养基并不特别适合于应用

Remedial Treatment of Corroded Iron Objects by Environmental Aeromonas Isolates

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