The Potential Role of S-and Fe-Cycling Bacteria on the Formation of Fe-Bearing Mineral (Pyrite and Vivianite) in Alluvial Sediments from the Upper Chicamocha River Basin, Colombia

S- and Fe-cycling bacteria can decisively affect the crystallization of Fe-bearing minerals in sediments from fluvial environments. We have studied the relationships between the Fe-bearing mineral assemblage and the bacterial community composition in the sediments rich in organic matter from the upper Chicamocha river basin (Colombia). Rapid flowing sections of the river contain sediments that have a high redox potential, are poor in organic matter and are enriched in kaolinite and quartz. On the other hand, the mineral assemblage of the sediments deposited in the La Playa dam with a high content in organic matter is enriched in Fe-bearing minerals: a) vivianite and pyrite in the permanently flooded sediments of the dam and b) pyrite and goethite in the periodically emerged sediments. The bacterial community composition of these sediments reveals anthropic organic matter pollution processes and biodegradation associated with eutrophication. Moreover, periodically emerged sediments in the La Playa dam contain bacterial groups adapted to the alternation of dry and wet periods under oxic or anoxic conditions. Cell-shaped aggregates with a pyritic composition suggest that sulfate-reducing bacteria (SRB) communities were involved in the precipitation of Fe-sulfides. The precipitation of vivianite in the flooded sediments was favored by a greater availability of Fe(II), which promoted the iron-reducing bacteria (IRB) enrichment of the sediments. The presence of sulfur-oxidizing bacteria (SOB) in the flooded sediments and the activity of iron-oxidizing bacteria (IOB) in the periodically emerged sediments favored both pyrite crystallization under a high sulfide availability and the oxidation of microbially precipitated monosulfides. Moreover, IOB enhanced goethite formation in the periodically emerged sediments.

The assessment of microbiological and physicochemical characteristics in drainage waters of the Siriu dam

Based on the balneotherapeutic applications of mineral spring water and particularly sulphurous water, the aim of our research was to study the physicochemical and microbiological parameters of some drainage waters of Siriu dam that showed a strong hydrogen sulphide odour. In addition, due to the corrosive effect of some groups of microorganisms, such as iron-oxidizing bacteria and sulphatereducing bacteria, the present paper also aimed to detect their presence in order to signal the need for some disinfection measures. According to physicochemical analysis, there has been found an external drain that is suitable for use in balneotherapy, presenting a balanced content of mineral elements such as sulphur, calcium, silicon, chlorine and potassium. However, due to the presence of potentially toxic phytoplankton microorganisms such as Microcystis sp. and Phormidium sp. it is necessary to disinfect this water source before using it for any purpose. On the other hand, the identification of both sulphate-reducing bacteria and iron-oxidizing bacteria in the drainage waters of Siriu dam should be considered as an alarm signal as they may lead to bio-corrosion and deterioration of metallic or concrete structures, affecting the integrity of the dam and hydropower constructions.

Bioleaching of E-Waste: Influence of Printed Circuit Boards on the Activity of Acidophilic Iron-Oxidizing Bacteria

Bioleaching is a promising strategy to recover valuable metals from spent printed circuit boards (PCBs). The performance of the process is catalyzed by microorganisms, which the toxic effect of PCBs can inhibit. This study aimed to investigate the capacity of an acidophilic iron-oxidizing culture, mainly composed of Leptospirillum ferriphilum, to oxidize iron in PCB-enriched environments. The culture pre-adapted to 1% (w/v) PCB content successfully thrived in leachates with the equivalent of 6% of PCBs, containing 8.5 g L–1 Cu, 8 g L–1 Fe, 1 g L–1 Zn, 92 mg L–1 Ni, 12.6 mg L–1 Pb, and 4.4 mg L–1 Co, among other metals. However, the inhibiting effect of PCBs limited the microbial activity by delaying the onset of the exponential iron oxidation. Successive subcultures boosted the activity of the culture by reducing this delay by up to 2.6 times under batch conditions. Subcultures also favored the rapid establishment of high microbial activity in continuous mode.

Iron Oxidation by a Fused Cytochrome-Porin Common to Diverse Iron-Oxidizing Bacteria

Iron is practically ubiquitous across Earth’s environments, central to both life and geochemical processes, which depend heavily on the redox state of iron. Although iron oxidation, or “rusting,” can occur abiotically at near-neutral pH, we find neutrophilic iron-oxidizing bacteria (FeOB) are widespread, including in aquifers, sediments, hydrothermal vents, pipes, and water treatment systems.

Carbonate polymorphism controlled by microbial iron redox dynamics at a natural CO2 leakage site (Crystal Geyser, Utah)

Crystal Geyser (Utah, USA) is a CO2-rich low-temperature geyser that is studied as a natural analog for CO2 leakage from carbon capture and storage (CCS) sites. In order to better constrain the biogeochemical processes influencing CaCO3 precipitation at geological CO2 escape sites, we characterized fast-forming iron-rich calcium carbonate pisoids and travertines precipitating from the fluids expelled by the geyser. The pisoids, located within a few meters from the vent, are composed of concentric layers of aragonite and calcite. Calcite layers contain abundant ferrihydrite shrubs in which iron is encasing bacterial forms. The aragonite layers contain less abundant and finely dispersed iron, present either as iron-oxide microspherules or iron adsorbed to organic matter dispersed within the carbonate matrix. We propose that carbonate polymorphism in the pisoids is mostly controlled by local fluctuations of the iron redox state of the fluids from which they form, caused by episodic blooms of iron-oxidizing bacteria. Indeed, the waters expelled by Crystal Geyser contain >200 µM dissolved iron (Fe2+), a known inhibitor of calcite growth. The calcite layers of the pisoids may record episodes of intense microbial iron oxidation, consistent with observations of iron-oxide rich biofilms thriving in the rimstone pools around the geyser and previous metagenomic analyses showing abundant neutrophilic, microaerophilic iron-oxidizing bacteria in vent water. In turn, aragonite layers of the pisoids likely precipitate from Fe2+-rich waters, registering periods of less intense iron oxidation. Separately, CaCO3 polymorphism in the travertines, where calcite and aragonite precipitate concurrently, is not controlled by iron dynamics, but may be locally influenced by the presence of microbial biofilms. This study documents for the first time an influence of microbial iron oxidation on CaCO3 polymorphism in the environment, and informs our understanding of carbonate formation at CO2 leakage sites and in CCS contexts.

Respiratory Heme A-Containing Oxidases Originated in the Ancestors of Iron-Oxidizing Bacteria

Respiration is a major trait shaping the biology of many environments. Cytochrome oxidase containing heme A (COX) is a common terminal oxidase in aerobic bacteria and is the only one in mammalian mitochondria. The synthesis of heme A is catalyzed by heme A synthase (CtaA/Cox15), an enzyme that most likely coevolved with COX. The evolutionary origin of COX in bacteria has remained unknown. Using extensive sequence and phylogenetic analysis, we show that the ancestral type of heme A synthases is present in iron-oxidizing Proteobacteria such as Acidithiobacillus spp. These bacteria also contain a deep branching form of the major COX subunit (COX1) and an ancestral variant of CtaG, a protein that is specifically required for COX biogenesis. Our work thus suggests that the ancestors of extant iron-oxidizers were the first to evolve COX. Consistent with this conclusion, acidophilic iron-oxidizing prokaryotes lived on emerged land around the time for which there is the earliest geochemical evidence of aerobic respiration on earth. Hence, ecological niches of iron oxidation have apparently promoted the evolution of aerobic respiration.