ANAEROBIC METABOLISM OF PRIMARY AND SECONDARY FORMS OF PHOTORHABDUS-LUMINESCENS

An oxygen electrode inserted into a dead Manduca sexta larva infected with Heterorhabditis nematodes carrying the bacterium Photorhabdus lum inescens showed barely detectable levels of oxygen in a 1 to 2 mm zone below the cuticle, and virtual anaerobiosis deeper in the carcass. Th is observation indicates that the bacteria in this habitat, where they are actively growing, are probably carrying out a fermentative metabo lism. Therefore, the anaerobic metabolism of the primary and secondary form variants of P. luminescens Hm and NCl was compared. Amino acids were not fermented by either strain, either singly or in mixtures. Glu cose was fermented by both forms of both organisms, forming products t ypical of mixed acid fermentation by Enterobacteriaceae. The fermentat ion patterns were the same in the primary and secondary forms. Growth rates of the secondary form cells were higher in defined medium with g lucose as energy and carbon source. Growth yields of the primary and s econdary forms of strain Hm were nearly identical, whereas the growth yield of secondary form cells of strain NCl was slightly higher than t hat of the primary form. The results of this study indicate that the o bserved predominance of primary form cells in infected insect larvae c annot be explained by an advantage over the secondary form cells relat ed to the efficiency of anaerobic growth or fermentative metabolism.