Immuno-electron microscopic identification of Methanosarcina spp. in anaerobic digester fluid

Whole cell antibodies against Methanosarcina mazei strain S6 were used with protein A – colloidal gold to identify bacteria in thin sections of samples from anaerobic methane producing digesters. It was possible to identify bacteria at the genus level and to show relatedness at the species and strain levels. Heavy labelling was observed on thin sections of the immunogenic strain S6. Lighter labelling was observed with pure cultures of M. mazei strain LYC. Pure cultures of Methanococcus voltae or Methanobacterium thermoautotrophicum did not label. In samples from mesophilic sewage digesters, sarcinal colonies of bacteria similar to Methanosarcina showed heavy labelling per cell while colonies from 55 °C digesters show lighter labelling. A few free cocci, which were released from the sarcinal colonies, also labelled. Labelling was not observed on other bacterial forms in either set of digesters. These studies indicate that a collection of bacterial antibodies can be used to identify and map bacteria in situ in mixed samples.