Poly-b-hydroxybutyrate accumulation and releasing by hydrogen producing bacteria, Rhodobacter sphaeroides O.U.001. A transmission electron microscopic study

Abstract

Photosynthetic bacterium Rhodobacter sphaeroides O.U.001 that is used for photobiohydrogen production can also accumulate poly-b-hydroxybutyrate (PHB) as a by-product when cultivated anaerobically with minimal medium containing L-malic acid, sodium glutamate and some vitamins under illumination. Transmission electron microscopy studies revealed that PHB granules are made of two distinct components: a homogenous and electron lucent core is covered with a more electron dense coat. PHB granules were observed in the cytoplasm, outside of the cells, in the center of cotton like aggregates in the cells, or while they were being released from the cell. In this study, two kinds of releasing were revealed; with lysis and without lysis of cell wall. Release of intact polymer outside the cells could be economically feasible way to obtain PHB for industrial applications.