Oligobody-A Nanostructure Found in a Super Oligotrophic Bacteria

Abstract

Oligotrophs means the bacteria that can utilize a very low concentration of carbon source and we are attempting to isolate oligotrophs from various environments. Among them, Rhodococcus erythropolis N9T-4, isolated from stored crude oil, shows super oligotrophic features and can grow on a basal medium without any additional carbon, nitrogen, sulfur, and energy sources, but requires CO₂ for its oligotrophic growth. Transmission electron microscopic observation showed that a relatively large and spherical nanostructure was observed in a N9T-4 cell grown under oligotrophic conditions. We termed this unique bacterial nanostructure an oligobody. The oligobody was not observed, or very rarely observed in small sizes under nutrient rich conditions, whereas additional carbon sources did not affect oligobody formation. Energy dispersive X-ray spectroscopy analysis suggested that the oligobody is composed of inorganic polyphosphate and is a type of acidocalcisome. Two genes encoding polyphosphate kinases, ppk1 and ppk2, were found in the N9T-4 genome: ppk1 disruption caused a negative effect on the formation of the oligobody. Although it was suggested that the oligobody plays an important role for the oligotrophic growth, both ppk-deleted mutants showed the same level of oligotrophic growth as the wild-type strain.