Minh Thi Tuyet Phan

Polyhydroxyalkanoates (PHAs) are biodegradable microbial polyesters that may reduce dependence on petroleum-derived plastics, but broader use remains constrained by production costs and tightly controlled cultivation. Thermophilic microorganisms have attracted increasing attention as promising PHA producers because they can be cultivated at elevated temperatures, reducing contamination risks and operational costs. In this study, a thermophilic Geobacillus sp. strain SL28 isolated from a Vietnamese hot spring was evaluated for its PHA-producing capability. Temperature, initial pH, carbon and nitrogen sources, C/N ratio, and cultivation time were examined. Intracellular inclusions were assessed by Sudan Black B and Nile Blue A staining and transmission electron microscopy, whereas the recovered polymer was characterized by FE-SEM, Fourier-transform infrared spectroscopy (FTIR), gas chromatography–mass spectrometry (GC–MS), ¹H- and ¹³C-nuclear magnetic resonance (NMR) spectroscopy, capillary viscometry, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and tensile testing. Under the optimized cultivation conditions identified by one-factor experimentation (50 °C, pH 7.0, sucrose, peptone, C/N 25:1, and 72 h), SL28 reached a dry cell weight of 2.215 ± 0.16 g/L and a PHA concentration of 1.383 ± 0.04 g/L, equivalent to 62.57 ± 2.82% of DCW. Structural characterization confirmed that the recovered polymer was poly(3-hydroxybutyrate) (PHB). The purified PHB also exhibited favorable thermal stability, a relatively high molecular weight, and satisfactory mechanical properties. These results demonstrate the potential of thermophilic Geobacillus sp. SL28 as a promising candidate for PHB production.

Polyhydroxyalkanoates (PHAs) are biodegradable microbial polyesters that represent a promising sustainable alternative to petroleum-based plastics. Salterns, hypersaline environments, are recognized as significant sources of halotolerant microorganisms that can produce PHAs in high-salinity conditions; however, Vietnamese saltern ecosystems have not been extensively investigated. This research aimed to isolate and initially characterize salt-tolerant bacteria capable of synthesizing PHAs from the Hon Khoi saltern in Khanh Hoa Province, Vietnam. A total of 37 halotolerant bacterial isolates were obtained, and potential PHA-producing strains were initially screened using Sudan Black B and Nile Blue A. TEM microscopy was then employed to confirm the existence of PHA granules. Furthermore, FTIR spectroscopy and GC–MS/MS spectrometry were utilized to analyze the chemical structure and monomer composition of the extracted polymers. Six isolates were identified as PHA-producing bacteria, including Salinivibrio sp. HK101 and HK116, Halomonas sp. HK105, Priestia sp. HK125 and HK142, and Bacillus sp. HK130. These strains exhibited growth across 3–10% NaCl and temperatures from 25 to 45 °C. Priestia sp. HK142 and Salinivibrio sp. HK101 exhibited the most substantial PHA accumulation, achieving 50.72 ± 1.83% and 42.07 ± 1.8% of DCW, respectively. These results indicate that the Hon Khoi saltern represents a promising source of halotolerant PHA-producing bacteria with potential relevance for future biopolymer production studies.

Polyhydroxyalkanoates (PHAs) are biodegradable microbial polyesters that represent a promising sustainable alternative to petroleum-based plastics. Salterns, hypersaline environments, are recognized as significant sources of halotolerant microorganisms that can produce PHAs in high-salinity conditions; however, Vietnamese saltern ecosystems have not been extensively investigated. This research aimed to isolate and initially characterize salt-tolerant bacteria capable of synthesizing PHAs from the Hon Khoi saltern in Khanh Hoa province, Vietnam. A total of 37 halotolerant bacterial isolates were obtained, and potential PHA-producing strains were initially screened using Sudan Black B and Nile Blue A. TEM microscopy was then employed to confirm the existence of PHA granules. Furthermore, FTIR spectroscopy and GC–MS/MS spectrometry were utilized to analyze the chemical structure and monomer composition of the extracted polymers. Six isolates were identified as PHA-producing bacteria, including Salinivibrio sp. HK101 and HK116, Halomonas sp. HK105, Priestia sp. HK125 and HK142, and Bacillus sp. HK130. These strains exhibited growth across 3–10% NaCl and temperatures from 25 to 45 °C. Priestia sp. HK142 and Salinivibrio sp. HK101 exhibited the most substantial PHA accumulation, achieving 50.72 ± 1.83% and 42.07 ± 1.8% of DCW, respectively. These results indicate that the Hon Khoi saltern represents a promising source of halotolerant PHA-producing bacteria with potential relevance for future biopolymer production studies.

Biotechnological applications of cytochromes P450 show difficulties, such as low activity, thermal and/or solvent instability, narrow substrate specificity and redox partner dependence. In an attempt to overcome these limitations, an exploitation of novel thermophilic P450 enzymes from nature via uncultured approaches is desirable due to their great advantages that can resolve nearly all mentioned impediments. From the metagenomics library of the Binh Chau hot spring, an open reading frame (ORF) encoding a thermostable cytochrome P450—designated as P450-T3—which shared 66.6% amino acid sequence identity with CYP109C2 of Sorangium cellulosum So ce56 was selected for further identification and characterization. The ORF was synthesized artificially and heterologously expressed in Escherichia coli C43(DE3) using the pET17b system. The purified enzyme had a molecular weight of approximately 43 kDa. The melting temperature of the purified enzyme was 76.2 °C and its apparent half-life at 60 °C was 38.7 min. Redox partner screening revealed that P450-T3 was reduced well by the mammalian AdR-Adx_4-108 and the yeast Arh1-Etp1 redox partners. Lauric acid, palmitic acid, embelin, retinoic acid (all-trans) and retinoic acid (13-cis) demonstrated binding to P450-T3. Interestingly, P450-T3 also bound and converted testosterone. Overall, P450-T3 might become a good candidate for biocatalytic applications on a larger scale.