Cross section through a bacterial mat in the Sippewisset salt marsh near Woods hole, massachusetts. The layers are as follows: top cyanobacteria; pink, phototrophic purple sulfur bacteria attached to sand grains; black, sulfate-reducing bacteria; peach, pacteriochlorphyll bcontaining cells of Thiocapsa pfennigiiCross section through a bacterial mat in the Sippewisset salt marsh near Woods Hole, Massachusetts. The layers are as follows: top, cyanobacteria; pink, phototrophic purple sulfur bacteria attached to sand grains; black, sulfate-reducing bacteria; peach, bacteriochlorphyll bcontaining cells of Thiocapsa pfennigii