Current Advances towards 4-Hydroxybutyrate Containing Polyhydroxyalkanoates Production for Biomedical Applications

Polyhydroxyalkanoates (PHA) are polyesters having high promise in biomedical applications. Among different types of PHA, poly-4-hydroxybutyrate (P4HB) is the only polymer that has received FDA approval for medical applications. However, most PHA producing microorganisms lack the ability to synthesize P4HB or PHA comprising 4-hydroxybutyrate (4HB) monomer due to their absence of a 4HB monomer supplying pathway. Thus, most microorganisms require supplementation of 4HB precursors to synthesize 4HB polymers. However, usage of 4HB precursors incurs additional production cost. Therefore, researchers have adopted strategies to reduce the cost, such as utilizing low-cost substrate as well as constructing 4HB monomer supplying pathways in microorganisms. We herein summarize the biomedical applications of P4HB, the natural producers of 4HB polymer, and the various strategies that have been applied in producing 4HB polymers in non-4HB producing microorganisms. It is expected that the readers would gain a vivid idea on the different strategic developments in the field of 4HB polymer production.

Germination of Corymbia citriodora on different substracts

The objective of the present work was to evaluate the germination of lemon-scented gum (Corymbia citriodora) on different substrates. The following were tested: 1) commercial substrate, 2) sand, 3) sand + coconut fiber (2: 1), 4) coconut fiber, 5) substrate + coconut fiber (2: 1), 6) sand + substrate (2: 1) and the control treatment (germitest paper). Based on the experiment, it was observed that germination varied between 57 and 74%, although there was no significant difference between treatments. The treatments that led to a higher germination speed were the control (germitest paper), followed by the commercial substrate, coconut fiber, sand + substrate and substrate + fiber, with no significant difference, indicating that they are the best for the germination of C. citriodora seeds. The substrate based on coconut fiber is promising, as it can be considered an alternative and low-cost substrate.

Glycerol promoted the anaerobic production of rhamnolipids by different Pseudomonas aeruginosa strains

Background: Rhamnolipids is the most widely studied and applied biosurfactants. The anaerobic biosynthesis of rhamnolipids has important research and practical significance, such as meeting the in situ production of biosurfactant in anoxic environments and the foamless fermentation of biosurfactants. A few studies have reported the anaerobic biosynthesis of rhamnolipids from rare Pseudomonas aeruginosa strains. What did promote the anaerobic biosynthesis of rhamnolipids, the specificity of the rare strains or the effect of specific substrates? Here, anaerobic production of rhamnolipids by different P. aeruginosa strains was investigated using diverse substrates. The anaerobic biosynthesis mechanism of rhamnolipids were also discussed from the substrate point of view.Results: All P. aeruginosa strains anaerobically grew well using the tested substrates. But all P. aeruginosa strains anaerobically produced rhamnolipids only using substrates containing glycerol and nitrate. Fourier transform infrared (FTIR) spectra analysis confirmed the anaerobic production of rhamnolipids from all P. aeruginosa strains. All the anaerobically produced rhamnolipids decreased air-water surface tension from 72.6 mN/m to below 29.0 mN/m and emulsified crude oil with EI24 above 65%. Using crude glycerol as low-cost substrate, all P. aeruginosa strains can anaerobically grow and produce rhamnolipids to reduce the culture surface tension below 35 mN/m. The glycerol metabolic intermediate, 1, 2-propylene glycol, can also achieve the anaerobic production of rhamnolipids by all P. aeruginosa strains.Conclusions: Not the specificity of the rare P. aeruginosa strains but the effect of specific substrates promote the anaerobic biosynthesis of rhamnolipids by P. aeruginosa. Glycerol and nitrate are the excellent substrates for anaerobic production of rhamnolipids from all P. aeruginosa strains. Results indicated that glycerol metabolism involveed the anaerobic biosynthesis of rhamnolipids in P. aeruginosa. Results also showed the feasibility of using crude glycerol as low cost substrate to anaerobically biosynthesize rhamnolipids by P. aeruginosa.