Chromate (Cr(VI)), as one of ubiquitous
contaminants in groundwater,
has posed a major threat to public health and ecological environment.
Although various electron donors (e.g., organic carbon, hydrogen,
and methane) have been proposed to drive chromate removal from contaminated
water, little is known for microbial chromate reduction coupled to
elemental sulfur (S(0)) or zerovalent iron (Fe(0)) oxidation. This
study demonstrated chromate could be biologically reduced by using
S(0) or Fe(0) as inorganic electron donor. After 60-day cultivation,
the sludge achieved a high Cr(VI) removal efficiency of 92.9 ±
1.1% and 98.1 ± 1.2% in two independent systems with S(0) or
Fe(0) as the sole electron donor, respectively. The deposited Cr(III)
was identified as the main reduction product based on X-ray photoelectron
spectroscopy. High-throughput 16S rRNA gene sequencing indicated that
Cr(VI) reduction coupled to S(0) or Fe(0) oxidation was mediated synergically
by a microbial consortia. In such the consortia, S(0)- or Fe(0)-oxidizing
bacteria (e.g., Thiobacillus or Ferrovibrio) could generate volatile fatty acids as metabolites, which were
further utilized by chromate-reducing bacteria (e.g., Geobacter or Desulfovibrio) to reduce chromate. Our findings
advance our understanding on microbial chromate reduction supported
by solid electron donors and also offer a promising process for groundwater
remediation.