Microbial communities within iron ore caves and associated iron-reducing enrichments

There are more than 3,000 iron ore caves (IOCs) within the banded iron formations (BIF) and associated iron rich deposites of Brazil. Unlike classical solution caves that form through the biotic dissolution of limestone, BIFs are poorly soluble and have low weathering rates, making it unlikely that IOCs form through strictly abiotic processes. Iron-reducing microorganisms (FeRM) are capable of reducing insoluble iron(III) to soluble iron(II). FeRM metabolism combined with the movement of ground water and associated removal of soluble Fe(II) could account for the formation of the IOCs. We examined the IOC microbial communities through molecular and culture-based techniques to determine if FeRM are present within the IOCs. gDNA was extracted from an IOC biofilm and two IOC pools of water. Samples from these locations were also collected and used as inocula in a variety iron enrichments designed to culture FeRM. Five of the initial enrichment cultures that demonstrated a range of iron-reducing capability were passaged in glucose-amended media. gDNA was subsequently extracted from initial enrichments and passaged cultures. gDNA from environmental samples, initial enrichments and passaged cultures underwent PCR amplification with the barcoded Illumina Bacterial/Archaeal 16S rRNA V4 region primers 515F and 806R, followed by sequencing on an Illumina MiSeq.