Ancestral States

Candidatus Accumulibacter phosphatis is one of our favorite bacteria in the McMahon Lab. This microbe plays a crucial role in wastewater treatment because it removes phosphorus from wastewater by accumulating polyphosphate (hence the name). The “candidatus” portion of its name means that it cannot be grown in pure culture. However, we can get it to grow in highly enriched cultures in bioreactors in the lab.

Accumulibacter is in yellow and green, representing the two of the types of Accumulibacter we see in reactors. Other bacteria are colored blue.

Accumulibacter is a fantastic microbe for wastewater treatment, but how did it become so good at its job? It’s highly unlikely that this organism evolved just to clean our wastewater, so its polyphosphate accumulating abilities must have provided an advantage in a different environment. Lab member Ben Oyserman’s paper begins to answer this question by reconstructing the ancestral genome of Accumulibacter based on modern genomes. One possibility was that Accumulibacter “copied” the genes to accumulate polyphosphate from another microbe that was already adapted to a high phosphorus environment (called horizontal gene transfer). However, Ben shows that the genes encoding the machinery for polyphosphate accumulation were most likely present in the ancestral state. Instead, the signature of horizontal gene transfer was present in pathways need to store carbon efficiently under anaerobic conditions. This analysis suggests that once these adaptations were in place, Accumulibacter could become a true polyphosphate accumulating organism.

This has implications both for other unrelated polyphosphate accumulating organisms that may have similar adaptations (called convergent evolution) and for engineering other microbes to be better at their jobs. Additionally, Ben’s methods could be used to investigate the evolution of other complex traits, or for understanding how best to engineer other microbes to have new traits.

Curious about the details? Check out Ben’s full paper here:

Oyserman, Ben O., et al. “Ancestral genome reconstruction identifies the evolutionary basis for trait acquisition in polyphosphate accumulating bacteria.” The ISME Journal (2016).