  Bacteria populate the colon where they replicate and migrate in response to
nutrient availability. Here I model the colon bacterial population as a
sandpile model, the colon-pile. Sand addition mimics bacterial replication and
grains toppling represents bacterial migration coupled to high population
density. The numerical simulations reveal a behaviour similar to
non-conservative sandpile models, approaching a critical state with system wide
avalanches when the death rate becomes negligible. The critical exponents
estimation indicates that the colon-pile belongs to a new universality class.
This work suggest that the colon microbiome is in a self-organised critical
state, where small perturbations can trigger large scale rearrangements,
covering an area comparable to the system size and characterised by a 1/f noise
spectra
