Influence of Seasonal and Geochemical Changes on the Geomicrobiology of an Iron Carbonate Mineral Water Spring

Abstract

Fuschna Spring in the Swiss Alps (Engadin region) is a bicarbonate iron(II)-rich, pH-neutral mineral water spring that is dominated visually by dark green microbial mats at the side of the flow channel and orange iron(III) (oxyhydr)oxides in the flow channel. Gradients of O 2 , dissolved iron(II), and bicarbonate establish in the water. Our goals were to identify the dominating biogeochemical processes and to determine to which extent changing geochemical conditions along the flow path and seasonal changes influence mineral identity, crystallinity, and microbial diversity. Geochemical analysis showed microoxic water at the spring outlet which became fully oxygenated within 2.3 m downstream. X-ray diffraction and Mössbauer spectroscopy revealed calcite (CaCO 3 ) and ferrihydrite [Fe(OH) 3 ] to be the dominant minerals which increased in crystallinity with increasing distance from the spring outlet. Denaturing gradient gel electrophoresis banding pattern cluster analysis revealed that the microbial community composition shifted mainly with seasons and to a lesser extent along the flow path. 16S rRNA gene sequence analysis showed that microbial communities differ between the flow channel and the flanking microbial mat. Microbial community analysis in combination with most-probable-number analyses and quantitative PCR (qPCR) showed that the mat was dominated by cyanobacteria and the channel was dominated by microaerophilic Fe(II) oxidizers (1.97 ؋ 10 7 ؎ 4.36 ؋ 10 6 16S rRNA gene copies g ؊1 using Gallionella-specific qPCR primers), while high numbers of Fe(III) reducers (10 9 cells/g) were identified in both the mat and the flow channel. Phototrophic and nitrate-reducing Fe(II) oxidizers were present as well, although in lower numbers (10 3 to 10 4 cells/g). In summary, our data suggest that mainly seasonal changes caused microbial community shifts, while geochemical gradients along the flow path influenced mineral crystallinity.

Ecological succession among iron-oxidizing bacteria

“…Other studies on FeOB communities (both neutrophilic and acidophilic) have observed general changes in community structure that correspond with temperature, season or rain (Edwards et al, 1999;Hegler et al, 2012;Johnson et al, 2012). In particular, Gault et al (2012) sampled a spring-fed iron mat in Chalk River, Ontario, once during each major season, and noted that the abundance of Gallionellales clones was greater in winter than in summer, consistent with the findings presented here.…”

Coexistence of Microaerophilic, Nitrate-Reducing, and Phototrophic Fe(II) Oxidizers and Fe(III) Reducers in Coastal Marine Sediment

“…These bacteria face the problem that, at neutral pH, the abiotic reaction of oxygen and Fe(II) is fast. Therefore, bacterial Fe(II) oxidation with O 2 at neutral pH is limited to micro-oxic ([O 2 ] Ͻ 50 M) conditions, where microbial iron oxidation can compete favorably with the [O 2 ]-limited abiotic reaction (13,14). Favorable conditions for the growth of microaerophilic Fe(II) oxidizers are found in opposing gradients of Fe(II) and O 2 , e.g., in the oxicanoxic transition zone in sediments or groundwater seeps (15).…”

Microbial Iron Oxidation in the Arctic Tundra and Its Implications for Biogeochemical Cycling

“…Molecular ecology studies of temperate iron mats generally report that cyanobacteria make up a small percentage of the population (26,27). A recent study of an alpine spring (Fuschna Spring) in Switzerland found an interesting spatial relationship between a phototrophic iron mat that grew along the edge of the spring channel and an iron mat that grew in its center (28). Despite being separated by a centimeter or less, the populations in the phototrophic mat were quite unique from those in the iron mat community, indicating that there might be close physical proximity of the different communities without much intermixing of populations.…”