Acid‐tolerant microaerophilic Fe(II)‐oxidizing bacteria promote Fe(III)‐accumulation in a fen

Abstract

The ecological importance of Fe(II)-oxidizing bacteria (FeOB) at circumneutral pH is often masked in the presence of O(2) where rapid chemical oxidation of Fe(II) predominates. This study addresses the abundance, diversity and activity of microaerophilic FeOB in an acidic fen (pH ∼ 5) located in northern Bavaria, Germany. Mean O(2) penetration depth reached 16 cm where the highest dissolved Fe(II) concentrations (up to 140 µM) were present in soil water. Acid-tolerant FeOB cultivated in gradient tubes were most abundant (10(6) cells g(-1) peat) at the 10-20 cm depth interval. A stable enrichment culture was active at up to 29% O(2) saturation and Fe(III) accumulated 1.6 times faster than in abiotic controls. An acid-tolerant, microaerophilic isolate (strain CL21) was obtained which was closely related to the neutrophilic, lithoautotrophic FeOB Sideroxydans lithotrophicus strain LD-1. CL21 oxidized Fe(II) between pH 4 and 6.0, and produced nanoscale-goethites with a clearly lower mean coherence length (7 nm) perpendicular to the (110) plane than those formed abiotically (10 nm). Our results suggest that an acid-tolerant population of FeOB is thriving at redox interfaces formed by diffusion-limited O(2) transport in acidic peatlands. Furthermore, this well-adapted population is successfully competing with chemical oxidation and thereby playing an important role in the microbial iron cycle.

Functional Gene Analysis of Freshwater Iron-Rich Flocs at Circumneutral pH and Isolation of a Stalk-Forming Microaerophilic Iron-Oxidizing Bacterium

“…S5 in the supplemental material), providing further evidence of autotrophy by FeOB. Although one member of the Gallionella-related group, "Candidatus Nitrotoga arctica," is a nitrite-oxidizing bacterium (60), to date, most isolates related to Gallionella are chemolithoautotrophic microaerophilic FeOB (6,10,17,59), strongly suggesting that the 16S and cbbM sequences also represent this metabolism. The physiological characteristics of OYT1 are similar to those of other freshwater microaerophilic FeOB isolates growing at circumneutral pH, such as R-1, S. lithotrophicus strains ES-1 and LD-1, G. capsiferriformans strain ES-2, and Sideroxydans paludicola strain BrT (6,10,17).…”

Chemolithotrophic nitrate-dependent Fe(II)-oxidizing nature of actinobacterial subdivision lineage TM3

“…Sideroxydans spp. are prevalent in iron-rich environments and prefer microaerophilic conditions (Emerson and Moyer, 1997;Weiss et al, 2007); furthermore, they have been detected in acidic peatlands indicating that some species are acidophilic or acid-tolerant (Lü decke et al, 2010). A previous study indicated that Gallionella ferruginea could perform autotrophic nitrate-dependent Fe(II) oxidation (Gouy et al, 1984), but no further studies with Gallionella have investigated this capability; however, studies have shown a complex distribution of Gallionella in relationship to the redox zonation in wetland soils (Wang et al, 2009), which is consistent with the existence of anaerobic phylotypes.…”

“…In the deeper layers of the sediment, Fe(II) oxidation is known to happen in the rhizosphere of plants by root released O 2 (Frenzel et al, 1999;Neubauer et al, 2007;Weiss et al, 2007) or in the sediment by nitrate-dependent Fe(II) oxidation by organisms growing either autotrophically or heterotrophically (Straub et al, 1996;Benz et al, 1998). An increasing body of literature over the last decade has shown that biogenic Fe(II) oxidation could have a more prominent role in iron cycling than considered previously, especially in low-pH environments (Lu et al, 2010;Lü decke et al, 2010).…”

Ecological succession among iron-oxidizing bacteria

“…Some Gal221-labeled cells were bean-shaped and attached to the end of helical stalks, typical of G. ferruginea, whereas other Gal221-labeled cells were more rod-shaped, consistent with the morphology of Sideroxydans spp., associated with particulate Fe(III)-oxyhydroxides (Weiss et al, 2007). It is important to note that several pure cultures of Gallionellales-related FeOB do not form stalks or identifiable Fe(III)-oxyhydroxide structures (Emerson and Moyer, 1997;Weiss et al, 2007;Lü decke et al, 2010); thus, the absence of stalks does not necessarily reflect the absence of this FeOB family. This may explain why Gallionellales FISH counts decreased with stalk disappearance but remained present throughout the remainder of the sampling season (Figure 2).…”