Evidence for Microbial Involvement in Pool Finger Precipitation,Hidden Cave,New Mexico

Although speleothems are usually considered inorganic precipitates, recent work has demonstrated hitherto unsuspected biogenic influence in some twilight areas. We have expanded this notion to the dark zone, examining pool fingers from Hidden Cave, New Mexico, to test for possible bacterial involvement. The pool fingers in Hidden Cave are pendant speleothems that formed subaqueously in paleo-pools. They are 1 to 4 cm in diameter and 5 to 50 cm long. A knobby, irregular external shape is underlaid by a layered interior on two scales, a 0.5 to 1.0 cm alternation between dense and porous layers and a mm-scale alternation between dark micritic calcite and clear dogtooth spar. The micrite is similar to microbialites identified in modern and ancient carbonates. Fossil bacteria were found in all layers. These include (1) calcified filaments 1 w m in diameter and 5–50 w m long and (2) micro-rods 0.1 w m by 1–2 w m. Most filaments are curved rods with a smooth surface but rare examples display a diamond crosshatch surface. The micro-rods occur as isolated crystals to dense meshes. We interpret the micro-rods as calcified bacilliform bacteria and the filaments as calcified filamentous bacteria. Carbon isotopic data are slightly more negative (by - 0.5 to - 1.0% in micritic layers than in dogtooth spar layers, suggesting a greater microbial influence in the micritic layers. Based on these similarities to known microbialites (e.g., petrographic fabrics, the presence of fossil bacteria, and the suggestive carbon isotopic data), we conclude that microbial activity was an intimate part of pool finger formation in Hidden Cave. The significance of such involvement goes beyond speleological contexts to wider questions of identification of biosignatures in rocks on earth and beyond.     

Novel, Attached, Sulfur-Oxidizing Bacteria at Shallow Hydrothermal Vents Possess Vacuoles Not Involved in Respiratory Nitrate Accumulation

Novel, vacuolate sulfur bacteria occur at shallow hydrothermal vents near White Point, Calif. There, these filaments are attached densely to diverse biotic and abiotic substrates and extend one to several centimeters into the surrounding environment, where they are alternately exposed to sulfidic and oxygenated seawater. Characterizations of native filaments collected from this location indicate that these filaments possess novel morphological and physiological properties compared to all other vacuolate bacteria characterized to date. Attached filaments, ranging in diameter from 4 to 100 μm or more, were composed of cylindrical cells, each containing a thin annulus of sulfur globule-filled cytoplasm surrounding a large central vacuole. A near-complete 16S rRNA gene sequence was obtained and confirmed by fluorescent in situ hybridization to be associated only with filaments having a diameter of 10 μm or more. Phylogenetic analysis indicates that these wider, attached filaments form within the gamma proteobacteria a monophyletic group that includes all previously described vacuolate sulfur bacteria (the genera Beggiatoa, Thioploca, and Thiomargarita) and no nonvacuolate genera. However, unlike for all previously described vacuolate bacteria, repeated measurements of cell lysates from samples collected over 2 years indicate that the attached White Point filaments do not store internal nitrate. It is possible that these vacuoles are involved in transient storage of oxygen or contribute to the relative buoyancy of these filaments.     

Investigation of iron-containing products from natural and laboratory cultivated Sphaerotilus-Leptothrix bacteria

Bacterial biomass collected from sheath-forming bacteria of the genera Sphaerotilus and Leptothrix was collected from a high-mountain natural stream water source. The elemental constitution and oxide phases of the products after selective cultivation of the bacteria on two different elective media using neutron activation analysis (NAA), electron microscopy (SEM, TEM), and X-ray diffraction (XRD) were studied. A high enrichment level of iron was revealed by the NAA technique in cultivated isolates as compared to the reference sample from nature. Three types of iron oxide compounds were established after cultivation in Adler’s medium: lepidocrocite (γ-FeOOH), magnetite (Fe₃O₄), and goethite (α-FeOOH). The cultivation in the Isolation medium yielded a single phase, that of goethite, excluding one sample with a distinguishable amount of lepidocrocite. XRD and EM investigations show that the biogenic oxides are nanosized. Our study exemplifies the possibilities of the biotechnology approach for obtaining, under artificial conditions, large quantities of iron-containing by-products that could be of further used in appropriate nano- and biotechnologies.     

Pollen tube extract supports the movement of actin filaments in vitro

Summary Muscle actin filaments labeled with rhodamine-phalloidin were observed to move on the surface coated with a crude extract of pollen tubes ofLilium longiflorum with an average velocity of 1.99±0.55 m/sec. The movement required both Mg²⁺ and ATP. These results indicate that the extract of pollen tubes contains a myosin-like translocatorAbbreviations ATP adenosine-5-triphosphate - DTT dithiothreitol - EGTA ethyleneglycol-bis-(-aminoethylether)N,N,N,N-tetraacetic acid - PIPES piperazine-N,N-bis-(2-ethanesulfonic acid) - PMSF phenylmethylsulfonyl fluoride     

Some Observations on the Occurrence of the Iron Bacterium Leptothrix ochracea in Fresh Water, including Reference to Large Experimental Enclosures

A study of iron bacteria in the hypolimnion of Blelham Tarn and 2 large experimental tubes therein showed that counts of Leptothrix ochracea filaments were proportional to total iron concentration. A regression equation was derived which described the relationship and from which 95% prediction limits of the counts could be obtained. This equation, however, failed to account for a significant proportion of the variability of the bacterial counts, nor could this be explained by changes in the other variables measured. Possible sources of variation are noted, as are results from a vertical profile from another productive lake and the reasons for the occurrence of significantly larger numbers of Leptothrix filaments in one of the enclosures. Changes in the appearance of the sheath of L. ochracea and the capsules of other iron bacteria with a similar distribution pattern, occurred when O₂ was absent from some samples.     

Protein filaments-structural components of the phloem exudate

Summary Fine structure and chemical composition of the phloem exudate of Cucurbita maxima and Nicotaiana glauca x suaveolens are investigated. Filamentous structures, several microns in length, are identified as structural components of the exudate by means of negative staining and electron microscopy. Two types of filaments are described: one form measures nearly 40 Å in diameter and shows a beaded appearance with regular spacings of about 50 Å; it is termed elementary filament. The second form has a diameter of about 90 Å and presumably consists of two helically arranged 40 Å subunits.The proteinaceous nature of the filaments is indicated by chemical analysis. The main macromolecular component of the exudate is demonstrated to be protein. Only traces of nucleic acids are detectable, lipids and polysaccharides cannot be found. The identity of the protein filaments with the filamentous structures (slime, P-protein), as revealed in thin sections of mature sieve tubes, is discussed.     

Structures of septin filaments prepared from rat brain and expressed in bacteria

Septin forms a conserved family of cytoskeletal GTP-binding proteins that have diverse roles in protein scaffolding, vesicle trafficking and cytokinesis. There are 14 mammalian septin isoforms and these isoforms assemble into hetero-oligomeric rod-shaped complexes and these short filaments are the basal units to construct higher-order structures such as longer filaments, rings, gauzes or hourglasses. Septin expressed in a eukaryotic expression system forms various structures such as bundles, sheets, helixes, and rings. Septin expressed in bacteria formed hexameric short filaments and single or parallel long filaments, but no such higher order structures were observed so far. In a previous study, we showed maturation-dependent localization of septin isoforms to the lipid raft fraction of rat brain. In this study, we attempted further purification of raft-localized septin isoforms. Repeated cycles of extraction with high MgCl₂ solution and precipitation under low ionic solution were combined with several column procedures. The obtained fraction contained several septin isoforms and showed rings of bundled filaments with a diameter of ～0.4 μm. Several non-septin proteins were also detected in the fraction. We also attempted expression of septin isoforms in bacteria and found that the expressed septin complexes formed bundles of filaments. In addition to linear and curled filaments, circular bundles of thin filaments with a diameter of ～0.6 μm were also observed. These results suggest that the curvature of the bundles of septin filaments may be regulated by the regulatory factor(s) in the lipid raft.     

Axenic culture of the bacteria associated with phony disease of peach and plum leaf scald

Bacteria associated with phony disease of peach (PDP) and plum leaf scald (PLS) were consistently isolated from diseased trees but not from healthy trees. Colonies of the bacteria grew slowly on PW agar, reaching 0.2 mm to 0.7 mm in diameter in 2 to 3 weeks. The bacteria did not grow on nutrient agar or other general-purpose media. Cells of the bacteria were 0.3 m to 0.4 m in width and 2.6 m to 20.0 m in length. The topography of the cell walls revealed numerous ridges and furrows. Cells extracted from diseased plants and those from culture gave a strong fluorescence when stained with immunoglobulin G to cells and purified membranes of the bacteria extracted from peach and plum in earlier studies. Immunoglobulin G to cells of the Pierce's disease bacterium from culture also reacted with the bacteria. No discernible differences were observed between strains associated with PDP and PLS in the United States and PLS in Brazil.     

Respiratory interactions of soil bacteria with (semi)conductive iron‐oxide minerals

Pure‐culture studies have shown that dissimilatory metal‐reducing bacteria are able to utilize iron‐oxide nanoparticles as electron conduits for reducing distant terminal acceptors; however, the ecological relevance of such energy metabolism is poorly understood. Here, soil microbial communities were grown in electrochemical cells with acetate as the electron donor and electrodes (poised at 0.2 V versus Ag/AgCl) as the electron acceptors in the presence and absence of iron‐oxide nanoparticles, and respiratory current generation and community structures were analysed. Irrespective of the iron‐oxide species (hematite, magnetite or ferrihydrite), the supplementation with iron‐oxide minerals resulted in large increases (over 30‐fold) in current, while only a moderate increase (～10‐fold) was observed in the presence of soluble ferric/ferrous irons. During the current generation, insulative ferrihydrite was transformed into semiconductive goethite. Clone‐library analyses of 16S rRNA gene fragments PCR‐amplified from the soil microbial communities revealed that iron‐oxide supplementation facilitated the occurrence of Geobacter species affiliated with subsurface clades 1 and 2. We suggest that subsurface‐clade Geobacter species preferentially thrive in soil by utilizing (semi)conductive iron oxides for their respiration.     

The distribution of P-Protein in mature sieve elements of celery

Summary The extent of blocking of sieve-plate pores caused by release of cell turgor was investigated by fixing and processing for electron microscopy a long length of celery (Apium graveolens L.) phloem. Differences in distribution of P-protein within the pores were observed between those cells near the two cut ends, and the central cells.To assess the effect of chemical fixation on the distribution of P-protein, strands of celery phloem (fixed or unfixed, and not treated with cryoprotectants) were frozen in Freon 12 and then freeze-substituted. In sieve elements from unfixed tissue there were a greater number of sieve plates displaying partially open pores.Direct freezing of unprotected phloem tissue in Freon 12 resulted in the formation of ice crystals within the lumen of the sieve elements. Freezing of tissue at rates fast enough to avoid the formation of damaging ice crystals resulted in sieve-plate pores having an unoccluded central channel with a peripheral lining of P-protein. In the lumen of the sieve elements the P-protein filaments occurred as discrete bundles ca. 0.5 m in diameter, and as a parietal layer varying in thickness from 0.1 to 0.5 m.     

Interaction of Aromatic Amines with Iron Oxides: Implications for Prebiotic Chemistry

The interaction of aromatic amines (aniline, p-chloroaniline, p-toludine and p-anisidine) with iron oxides (goethite, akaganeite and hematite) has been studied. Maximum uptake of amines was observed around pH 7. The adsorption data obtained at neutral pH were found to follow Langmuir adsorption. Anisidine was found to be a better adsorbate probably due to its higher basicity. In alkaline medium (pH?>?8), amines reacted on goethite and akaganeite to give colored products. Analysis of the products by GC–MS showed benzoquinone and azobenzene as the reaction products of aniline while p-anisidine afforded a dimer. IR analysis of the amine–iron oxide hydroxide adduct suggests that the surface acidity of iron oxide hydroxides is responsible for the interaction. The present study suggests that iron oxide hydroxides might have played a role in the stabilization of organic molecules through their surface activity and in prebiotic condensation reactions.     

Ultrastruktur glycerinextrahierter Dünndarmmuskelzellen der Ratte vor und nach Kontraktion

Zusammenfassung Die Tunica muscularis des Dünndarms der Ratte wurde elektronenmikroskopisch vor und nach Glycerinextraktion und nach verschieden lang andauernder ATP-Behandlung untersucht. Vor und nach der Extraktion sind nur 50–80 Å breite F-Actin-Filamente in den glatten Muskelzellen nachzuweisen. Die extrahierten glatten Muskelzellen kontrahieren sich nach Zugabe von ATP. Gleichzeitig treten in der Längsrichtung der Zelle verlaufende 150–200 Å dicke Myosinfilamente auf. Während langanhaltender Inkubation mit ATP trennen sich Actin- und Myosinfilamente zunächst voneinander durch eine Art Gleitmechanismus, da die Actinfilamente noch an der Zellmembran verhaftet bleiben, die Myosinfilamente sich aber verschieben. Dann lösen sich die Actinfilamente von der Zellmembran und Actin- und Myosinfilamente bilden ein dichtes Netzwerk im Zentrum der Zelle. In der Umgebung dieses Netzwerkes verbleiben feine Filamente mit einem Durchmesser von 20–30 Å.

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Ultrastructure of glycerinated small intestine muscle cells of the rat before and after contraction

Summary Tunica muscularis of the rat's small intestine was studied electron microscopically before and after glycerol-extraction and at various times after ATP treatment. Before and after extraction only F-actin-filaments with a diameter of 50–80 Å could be found in smooth muscle cells. Dense bodies disappear during extraction. Glycerinated smooth muscle cells contract when ATP is added. At the same time thick filaments with a diameter of 150–200 Å appear, which probably represent myosin filaments, running longitudinally within the cells. During prolonged ATP treatment actin and myosin filaments first separate from each other by a sort of sliding mechanism because actin filaments are still bound to the cell membrane while myosin filaments move. Then actin filaments are drawn off from the cell membrane and actin and myosin filaments assemble in an intricate network of filaments in the central part of the cell. Around this network fine filaments with a diameter of 20–30 Å remain.

Für die technische Mithilfe danke ich Frau Karla Struwe.     

The role of biomineralization in microbiologically influenced corrosion

Synthetic iron oxides (goethite, -FeO·OH; hematite, Fe₂O₃; and ferrihydrite, Fe(OH)₃) were used as model compounds to simulate the mineralogy of surface films on carbon steel. Dissolution of these oxides exposed to pure cultures of the metal-reducing bacterium, Shewanella putrefaciens, was followed by direct atomic absorption spectroscopy measurement of ferrous iron coupled with microscopic analyses using confocal laser scanning and environmental scanning electron microscopies. During an 8-day exposure the organism colonized mineral surfaces and reduced solid ferric oxides to soluble ferrous ions. Elemental composition, as monitored by energy dispersive x-ray spectroscopy, indicated mineral replacement reactions with both ferrihydrite and goethite as iron reduction occurred. When carbon steel electrodes were exposed to S. putrefaciens, microbiologically influenced corrosion was demonstrated electrochemically and microscopically.     

Filament arrangements in negatively stained cultured cells: the organization of actin

Treatment of spread, cultured cells with Triton X-100 followed by negative staining reveals the organization of the unextracted intracellular filamentous elements: actin, microtubules and the 100 angstrom filaments. The present report describes the organization of the actin-like filaments in human skin fibroblasts and mouse 3 T 3 cells. As shown in earlier studies, the cytoplasmic stress fibres were seen to be composed of bundles of colinear actin-like filaments. In addition to these large stress fibres much smaller bundles of thin filaments as well as randomly oriented thin filaments were also observed. A thick bundle of thin filaments, 0.2 microm to 0.5 microm in diameter, was found to delimit the concave cell edges most prominent in well-spread stationary cells. The leading edge and ruffled border of human skin fibroblasts appeared as a broad web, of meshwork of diagonally oriented thin filaments interconnecting radiating, linear bundles of thin filaments about 0.1 microm in diameter. These bundles corresponding to the microspikes described earlier ranged from about 1.5 microm in length and were separated by 1 microm to 3 microm laterally. The leading edge of 3 T 3 cells showed a similar organization but with fewer radiating thin filament bundles. Both the filaments in the bundles and in the meshwork formed arrowhead complexes with smooth muscle myosin subfragment - 1 which were unipolar and directed towards the main body of the cell. The findings are discussed in relation to the mechanisms of non-muscle cell motility.     

Syntrophic Effects in a Subsurface Clostridial Consortium on Fe(III)-(Oxyhydr)oxide Reduction and Secondary Mineralization

In this study, we cultivated from subsurface sediments an anaerobic clostridial consortium that was composed of a fermentative Fe-reducer Clostridium species (designated as strain FGH) and a novel sulfate-reducing bacterium belonging to the clostridia family Vellionellaceae (designated as strain RU4). In pure culture, Clostridium sp. strain FGH mediated the reductive dissolution/transformation of iron oxides during growth on peptone. When Clostridium sp. FGH was grown with strain RU4 on peptone, the rates of iron oxide reduction were significantly higher. Iron reduction by the consortium was mediated by multiple mechanisms, including biotic reduction by Clostridium sp. FGH and biotic/abiotic reactions involving biogenic sulfide formed by strain RU4. The Clostridium sp. FGH produced hydrogen during fermentation, and the presence of hydrogen inhibited growth and iron reduction activity. The sulfate-reducing partner strain RU4 was stimulated by the presence of H₂and generated reactive sulfide which promoted the chemical reduction of the iron oxides. Characterization of Fe(II) mineral products showed the formation of nanoparticulate magnetite during ferrihydrite reduction, and the precipitation of iron sulfides during goethite and hematite reduction. The results suggest an important pathway for iron reduction and secondary mineralization by fermentative sulfate-reducing microbial consortia through syntrophy-driven biotic/abiotic reactions with biogenic sulfide.

Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the supplemental file.     

The preservation and degradation of filamentous bacteria and biomolecules within iron oxide deposits at Rio Tinto, Spain

One of the keys to understanding and identifying life on other planets is to study the preservation of organic compounds and their precursor micro-organisms on Earth. Rio Tinto in southwestern Spain is a well documented site of microbial preservation within iron sulphates and iron oxides over a period of 2.1 Ma. This study has investigated the preservation of filamentous iron oxidising bacteria and organics through optical microscopy, scanning electron microscopy (SEM) and Fourier transform infra-red (FTIR) spectroscopy, from laboratory cultures of natural samples to contemporary natural materials to million-year old river terraces. Up to 40% elemental carbon and >7% nitrogen has been identified within microbial filaments and cell clusters in all samples through SEM EDS analyses. FTIR spectroscopy identified C-H(x) absorption bands between 2960 and 2800 cm(-1), Amide I and II absorption bands at 1656 and 1535 cm(-1), respectively and functional group vibrations from within nucleic acids at 917, 1016 and 1124 cm(-1). Absorption bands tracing the diagenetic transformation of jarosite to goethite to hematite through the samples are also identified. This combination of mineralogy, microbial morphology and biomolecular evidence allows us to further understand how organic fossils are created and preserved in iron-rich environments, and ultimately will aid in the search for the earliest life on Earth and potential organics on Mars.     

Four-Hundred-and-Ninety-Million-Year Record of Bacteriogenic Iron Oxide Precipitation at Sea-Floor Hydrothermal Vents

Fe oxide deposits are commonly found at hydrothermal vent sites at mid-ocean ridge and back-arc sea floor spreading centers, seamounts associated with these spreading centers, and intra-plate seamounts, and can cover extensive areas of the seafloor. These deposits can be attributed to several abiogenic processes and commonly contain micron-scale filamentous textures. Some filaments are cylindrical casts of Fe oxyhydroxides formed around bacterial cells and are thus unquestionably biogenic. The filaments have distinctive morphologies very like structures formed by neutrophilic Fe oxidizing bacteria. It is becoming increasingly apparent that Fe oxidizing bacteria have a significant role in the formation of Fe oxide deposits at marine hydrothermal vents. The presence of Fe oxide filaments in Fe oxides is thus of great potential as a biomarker for Fe oxidizing bacteria in modern and ancient marine hydrothermal vent deposits. The ancient analogues of modern deep-sea hydrothermal Fe oxide deposits are jaspers. A number of jaspers, ranging in age from the early Ordovician to late Eocene, contain abundant Fe oxide filamentous textures with a wide variety of morphologies. Some of these filaments are like structures formed by modern Fe oxidizing bacteria. Together with new data from the modern TAG site, we show that there is direct evidence for bacteriogenic Fe oxide precipitation at marine hydrothermal vent sites for at least the last 490 Ma of the Phanerozoic.     

Biogenic Origin of Polymetallic Nodules from the Clarion-Clipperton Zone in the Eastern Pacific Ocean: Electron Microscopic and EDX Evidence

Polymetallic/ferromanganese nodules (Mn-nodules) have been assigned a huge economic potential since they contain considerable concentrations of manganese, copper, nickel, iron, and cobalt. It has been assumed that they are formed by, besides hydrogenous, nonbiogenic processes, biogenic processes based on metabolic processes driven by microorganisms. In the present study, we applied the techniques of digital optical microscopy and high-resolution scanning electron microscopy to search for microorganisms in Mn-nodules. They were collected from the Clarion-Clipperton Zone in the Eastern Pacific Ocean and are composed of Mn (23.9%), Cu (0.69%), Ni (1.02%), Fe (10.9%), and Co (0.29%). These Mn-nodules, between 2.3 and 4.8 cm, show a distinct lamination; they are composed of small-sized micronodules, 100 to 450 μm in size, which are bound together by an interstitial whitish material. In the micronodules, a dense accumulation of microorganisms/bacteria could be visualized. Only two morphotypes exist: (1) round-shaped cocci and (2) elongated rods. The cocci (diameter: ≈3.5 μm) are arranged in bead-like chains, while the rods (≈2 × 0.4 μm) are arranged either as palisades or in a linear row. Energy-dispersive X-ray spectroscopy analyses showed that the areas rich in microorganisms/bacteria are also rich in Mn, while in regions where no microorganisms are found, the element Si is dominant. We suggest that growth of the Mn-nodules starts with the formation of “micronodules.” The formation of micronodules is assumed to be mediated by microorganisms. After accretion of biogenic and additional nonbiogenic minerals, the micronodules assemble to large nodules on the sea floor through additional inclusion of nonbiogenic material.     

Novel, attached, sulfur-oxidizing bacteria at shallow hydrothermal vents possess vacuoles not involved in respiratory nitrate accumulation

Novel, vacuolate sulfur bacteria occur at shallow hydrothermal vents near White Point, Calif. There, these filaments are attached densely to diverse biotic and abiotic substrates and extend one to several centimeters into the surrounding environment, where they are alternately exposed to sulfidic and oxygenated seawater. Characterizations of native filaments collected from this location indicate that these filaments possess novel morphological and physiological properties compared to all other vacuolate bacteria characterized to date. Attached filaments, ranging in diameter from 4 to 100 microm or more, were composed of cylindrical cells, each containing a thin annulus of sulfur globule-filled cytoplasm surrounding a large central vacuole. A near-complete 16S rRNA gene sequence was obtained and confirmed by fluorescent in situ hybridization to be associated only with filaments having a diameter of 10 microm or more. Phylogenetic analysis indicates that these wider, attached filaments form within the gamma proteobacteria a monophyletic group that includes all previously described vacuolate sulfur bacteria (the genera Beggiatoa, Thioploca, and Thiomargarita) and no nonvacuolate genera. However, unlike for all previously described vacuolate bacteria, repeated measurements of cell lysates from samples collected over 2 years indicate that the attached White Point filaments do not store internal nitrate. It is possible that these vacuoles are involved in transient storage of oxygen or contribute to the relative buoyancy of these filaments.     

Surface chemistry and reactivity of bacteriogenic iron oxides from Axial Volcano, Juan de Fuca Ridge, north-east Pacific Ocean

Iron oxides were collected from the caldera of Axial Volcano, a site of hydrothermal vent activity along the Juan de Fuca Ridge. Mineralogical inspection using X‐ray diffraction (XRD) revealed the majority of samples to be 2‐line ferrihydrite, with one of the samples corresponding to poorly ordered goethite. Examination using environmental scanning electron microscopy (ESEM) found the constituents of the iron oxides to consist predominantly of bacterial‐like structures that resembled the iron oxidizing bacteria Leptothrix ochracea, Gallionella ferruginea and a novel PV‐1 strain. X‐ray photoelectron spectroscopy (XPS) detected the presence of Fe, O, C, N, Ca, Si and P on all the samples with the exception of poorly ordered goethite, where Ca and P were absent, in addition to a weak N peak. Binding energy shifts of the Fe 2p and O 1s peaks were indicative of ferrihydrite and hydroxyl functional groups, while the presence and speciation of the C 1s peak was attributed to the presence of bacteria. Use of acid‐base titration data modelling in conjunction with a linear programming regression method (LPM) indicated that the iron oxides are composed of heterogeneous surface functional groups. Differences in iron oxide reactivity values correlated with differences in the bacterial and mineral fabric of the samples. The diverse surface chemistry and high reactivity of these iron oxides may be important in the global cycling of various elements throughout the oceans due to their presence along widespread mid‐ocean ridges.