Direct observation of polyhydroxyalkanoate chains by atomic force microscopy

Kumar Sudesh¹, Zhihua Gan¹, Kenﾅfichiro Matsumoto², and Yoshiharu Doi¹

1) Polymer Chemistry Laboratory, RIKEN Institute, Hirosawa 2-1, Wako-shi, Saitama 351-0198, Japan
2) Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan

Atomic force microscopy in the tapping mode was used to investigate aqueous acetone-treated polyhydroxyalkanoate (PHA) inclusions freshly isolated from a recombinant bacterium. The PHA is a copolymer containing about 90~95 mol% 3-hydroxybutyrate units while the rest were units of 3-hydroxyhexanoate, 3-hydroxyoctanoate and 3-hydroxydecanoate. Polymer chains extending to more than 5 mm in length were observed on glass cover slips upon the evaporation of the aqueous acetone. The dimension of the thinnest strand was about 1 nm in height and 10 nm in apparent width. The results suggest that biosynthesized PHA are stored in the inclusions in an amorphous state but with minimal chain entanglement.