Best Friends Identified in Wastewater

One of the key characteristics of microbiomes is that they’re not just collections of diverse microbes doing their own things – there are complex networks of interactions between species within microbial communities, such as sharing or trading resources to benefit multiple species. Lab members Chris and Josh recently published their findings on one such interaction in the wastewater microbiome, specifically between Brocadia, which performs the anammox reaction, and Chlorobi, a green sulfur bacterium.

Both of these bacteria are cool in their own right. The story of what anammox is and how it was discovered in Brocadia is certainly worth a read (spoiler: they make rocket fuel and have traits of Eukaryotes and Archaea). Chlorobi is familiar to us from the freshwater side of the lab, where it seems to be performing more than its fair share of the metabolic reactions. But in anammox-based wastewater treatment, these two types of bacteria work together to remove ammonium from our wastewater. Even better, they do it without oxygen, one of the most expensive parts of wastewater treatment!

In this study, Chris, Josh, and our collaborators used metagenomics (sequencing all of the DNA in a sample) to piece together the genomes, and metatranscriptomics (sequencing all of the RNA in a sample) to predict which metabolic functions were performed by each community member. They found that the two most abundant and active groups, Brocadia and Chlorobi, form a “nitrite loop,” where Brocadia converts nitrite to nitrate as part of its anammox reaction, and Chlorobi recycles that nitrate back to nitrite. Additionally, Brocadia seems to be providing much of the carbon and amino acids consumed by the rest of the community in the form of extracellular proteins, while Chlorobi breaks down those proteins and makes amino acids available to the rest of the community. Interestingly, some of the bacteria found in our lab’s reactor in Madison were nearly identical to those found in a similar reactor in the Netherlands, suggesting that this relationship between Brocadia and Chlorobi is something that happens on a regular basis.

For our purposes of cleaning wastewater, Brocadia and Chlorobi seem like a perfect match! To learn more about this research, read the full paper here.

brocadia-chlorobi

Fig. 7 from the paper

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