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Thermotolerant bacteria producing medium-chain-length polyhydroxyalkanoate (mcl-PHA) were isolated from various thermal sites, including palm oil mill effluent, textile wastewater, and hot spring water, in Thailand. Fifteen strains were isolated at 45 °C using nutrient-rich (NR) medium. However, only six isolates produced mcl-PHA at 0.41 ± 0.01 g/L to 0.80 ± 0.01 g/L, representing a mcl-PHA content of 29.44% to 50.77% of the dry cell weight (DCW). The six strains of bacterial isolates could utilise a variety of substrates; all were identified as Bacillus thermoamylovorans. The highest mcl-PHA content (50.77% of the DCW) was accumulated by the B. thermoamylovorans strain PHA005 isolated from palm oil mill effluent. The mcl-PHA from strain PHA005 was composed of five different monomers, 3-hydroxyoctanoate (3HO), 3-hydroxydecanoate (3HD), 3-hydroxytetradecanoate (3HTD), 3-hydroxyhexadecanoic acid (3HHD), and 3-hydroxyoctadecanoic (3HOD), with a monomer content of 24.12, 15.50, 13.00, 39.25, and 8.13 mol%, respectively. The optimum temperature for B. thermoamylovorans strain PHA005 growth is 45 °C, and it can survive at up to 60 °C. This is a first report of PHA synthesis by a thermotolerant B. thermoamylovorans. Moreover, the high content of 3HHD monomers (39.25 mol%) has never been reported in Bacillus.

Screening of high-efficient polycyclic aromatic hydrocarbon (PAH)-degrading bacteria is important due to environmental contamination by PAHs. In this study, sediment contaminated with phenanthrene (Phe), pyrene (Pyr), and fluoranthene (Fluo) was used as a source of bacteria. The ability of these isolated bacteria to convert PAHs into valuable products was determined. Based on a primary screening, 20 bacterial isolates were obtained; however, only three strains showed a good PAH-degrading ability, and were identified as Pseudomonas aeruginosa, Pseudomonas sp., and Ralstonia sp. PAH-degrading genes were detected in all isolates. Notably, all selected strains could degrade PAHs using the ortho or meta cleavage pathways due to the presence of catechol dioxygenase genes. The ability of isolated strains to convert PAHs into polyhydroxyalkanoate (PHA) was also evaluated in both single and mixed cultures. Single cultures of P. aeruginosa PAH-P02 showed 100% degradation of PAHs, with the highest biomass (1.27 ± 0.02 g l -1 ) and PHA content (38.20 ± 1.92% dry cell weight). However, degradative ability and PHA production were decreased when mixtures of PAHs were used. This study showed that P. aeruginosa, Pseudomonas sp., and Ralstonia sp. were able to degrade PAHs and convert them into medium-chain-length (mcl)-PHA. A high content of 3-hydroxydecanoate (3HD, C10) was observed in this study. The formation of mcl-PHA with high 3HD content from Pyr and Fluo, and the assessment of mixed cultures converting PAHs to mcl-PHA, were novel contributions.