Orange leads to black: evaluating the efficacy of co‐culturing iron‐oxidizing and sulfate‐reducing bacteria to discern ecological relationships

Abstract

Two global cycles, iron and sulfur, are critically interconnected in estuarine environments by microbiological actors. To this point, the methods of laboratory study of this interaction have been limited. Here we propose a methodology for co-culturing from numerous coastal environments, from the same source inocula, iron-oxidizing and sulfatereducing bacteria. The use of same source inocula is largely beneficial to understand real-world interactions that are likely occurring in situ. Through the use of this methodology, the ecological interactions between these groups can be studied in a more controlled environment. Here, we characterize the oxygen and hydrogen sulfide concentrations using microelectrode depth profiling in the co-cultures of iron-oxidizing bacteria and sulfate-reducing bacteria. These results suggest that while oxygen drives the relationship between these organisms and sulfate-reducers are reliant on iron-oxidizers in this culture to create an anoxic environment, there is likely another environmental driver that also influences the interaction as the two remain spatially distinct, as trends in FeS precipitation changed within the anoxic zone relative to the presence of Fe(III) oxyhydroxides. Understanding the relationship between iron-oxidizing and sulfate-reducing bacteria will ultimately have implications for understanding microbial cycling in estuarine environments as well as in processes such as controlling microbially influenced corrosion.

Sulfur cycling likely obscures dynamic biologically‐driven iron redox cycling in contemporary methane seep environments

“…Given that sulfate‐reducing microorganisms (SRM) are abundant at methane seeps and that black precipitates are often used an indicator for SRM (Blackwell et al, 2020 ; Picard et al, 2016 , 2019 ; van Dongen et al, 2007 ), we suspected that these minerals were the product of Fe 2+ in the system reacting with sulfide produced by SRM. A recent study describing a novel gradient tube enrichment technique for co‐culturing SRM and FeOB observed a similar phenomenon, where black precipitates were only formed in the presence of SRM (Brooks & Field, 2021 ). We thus started a new lineage of cultures in sulfate‐depleted media (see Methods for details) to assess if the black material was indeed generated by the activity of SRM.…”

Microbial community response to hydrocarbon exposure in iron oxide mats: an environmental study

“…These result in total represent possible connections between hydrocarbons and the nitrogen, iron, and sulfur cycles and suggest that the community within the iron mat could potentially contribute to bioremediation of benzene or other hydrocarbons. Freshwater iron mats have been previously hypothesized to connect the iron and sulfur cycles (Koeksoy et al, 2018;Brooks and Field, 2021); however, connections to the nitrogen cycle have not been previously proposed. Of interest, future studies would be whether microbial activity rates in the iron mat are the same when exposed to hydrocarbons, given the previously discussed loss of diversity.…”