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Although xylose is a major constituent of lignocellulosic feedstock and the second most abundant sugar in nature, only 22% of 3,152 screened bacterial isolates showed significant growth in xylose in 24 h. Of those 684, only 24% accumulated polyhydroxyalkanoates after 72 h. A mangrove isolate, identified as Bacillus sp. MA3.3, yielded the best results in literature thus far for Gram-positive strains in experiments with glucose and xylose as the sole carbon source. When glucose or xylose were supplied, poly-3-hydroxybutyrate (PHB) contents of cell dry weight were, respectively, 62 and 64%, PHB yield 0.25 and 0.24 g g⁻¹ and PHB productivity (P_PHB) 0.10 and 0.06 g l⁻¹ h⁻¹. This 40% P_PHB difference may be related to the theoretical ATP production per 3-hydroxybutyrate (3HB) monomer calculated as 3 mol mol⁻¹ for xylose, less than half of the ATP/3HB produced from glucose (7 mol mol⁻¹). In PHB …