The Macropodid Oesophagus. II. Morphological Studies of Its Adherent Bacteria using Light and Electron Microscopy

Abstract

The bacterial population attached to the oesophageal lining in herbivorous macropods is described. This feature which occurs in both browsing and grazing macropodid species (Macropus, Seton ix, Thylogale and Wallabia) is demonstrated by light and electron microscopy. These studies have shown that the oesophagus may support a large and diverse population of bacterial forms, many of which have extracellular fibrous coats or homogeneous capsules. These coats and capsules appear to mediate the attachment of bacteria to the surface epithelium and to each other so that microcolonies or communities are formed. Such aggregations of bacteria are responsible for the greenish coloration of the oesophageal lining of these herbivorous species. Further examination of the bacterial association with oesophageal cells demonstrated that the bacteria did not invade the mucosa but merely colonized the superficial layer of cells. Cells with ruptured cell membranes were invaded by bacteria which appeared to digest the cytoplasmic contents. Sloughing of such cells provided a new surface for bacterial attachment and proliferation. The importance of this bacterial association is discussed in the light of the anatomical studies of the macropodid oesophagus and the known digestive processes of herbivorous macropods. It is proposed that this adaptation may have an important bearing on our knowledge of foregut fermentative digestion in macropods.