Fig. 2: Biodegradation of Poly[(R)-3-hydroxybutyrate-co-9 mol%-(R)−3-hydroxyhexanoate] (PHBH) injection-molded and melt-pressed film samples placed at the deep-sea floor and models of microbial degradation.

a Injection-molded samples were placed in the sea at different depths (2–5500 m) for about 1 year for biodegradation tests. See Table 1 for abbreviations regarding ___location and Table 2 for abbreviations regarding samples. b, c The original and PJM12, BHT14, and AMN13 injection-molded samples are shown in a photograph taken from (b) the top side and (c) the end, showing that the samples were reduced in size while maintaining their shape without physical collapse. d Surface SEM images show that decomposition proceeded regardless of water depth. e Photographs of an original film sample of 4 × 4 cm, after 250 days of placement on the deep-sea floor off Hatsushima Island at 855 m (BHT08), and after biofilm removal by ultrasonic washing, respectively. f The dimensions of the film in BHT08 (after washing) were the same as the original, meaning that no physical collapse occurred, but numerous penetrating holes were observed by stereomicroscopy. g Scanning electron microscope (SEM) images showing a magnified view of the surface of each PHBH film. While the surface of the original sample was smooth, microorganisms accumulated on the surface of the BHT08 sample, and the surface of the film, after the microorganisms were removed by ultrasonic washing (BHT08 After washing), showed the roughness typically observed following microbial degradation. h The decrease in weight (black line) and film thickness (red line) at the deep-sea bottom off Hatsushima Island over 8 months. Values are given as average of n = 4 independent samples with its standard deviation (Supplementary Data 1). i Illustrations of biodegradation corresponding to the photos and SEM images above. j BOD biodegradability curve, showing that PHBH (black dot) and cellulose (red dot) are completely converted to water and carbon dioxide by microorganisms in the seawater of Tokyo Bay. The micrographs are representative images from n = 3 independent samples with similar results. The BOD data is representative of one of n = 3, with similar results (Supplementary Data 2). Source data are provided as a Source Data file.