Blue meets green: Marine bacteria and biomass residues in sustainable polyhydroxyalkanoates synthesis

Introduction

The transition to a circular bioeconomy requires valorizing organic waste into high-value bioproducts. We studied marine bacteria and renewable carbon from lignocellulosic biomass to produce polyhydroxyalkanoates (PHA), biodegradable bioplastics. Two marine bacteria were selected: Cobetia marina (culture collection) and Roseibium alexandrii, isolated from a PHA biofilm after long-term marine exposure.

Methods

Over 50 isolates were screened for PHA accumulation using phaC gene detection and Nile red fluorescence. R. alexandrii was chosen for its consistent activity, with C. marina as reference. Both were grown on simple carbon sources (glucose, crotonic acid, gamma-valerolactone [GVL]) and complex sugars from organosolv-hydrolyzed cellulose. Different C/N ratios of 12.5, 25, and 50 were tested to assess nutrient balance effects. After 48 h, cell dry weight and Nile red fluorescence were measured, and PHA was extracted and analyzed by NMR spectroscopy.

Results

Overall, C/N 12.5 yielded the highest biomass and fluorescence in most conditions, especially with glucose, crotonic acid, and birch- or cellulose-derived fractions. C/N 25 showed moderate results, while 50 led to reduced growth and PHA synthesis. GVL alone was a poor substrate, but when present in low amounts within sugar mixtures, it did not interfere, enabling the direct use of spontaneously separated crude hydrolysates. Some of the sugar-rich fractions enabled biomass and PHA yields comparable or superior to glucose. Crotonic acid, a PHA degradation product, supported high PHA yields, suggesting a promising route to re-synthesize PHA from its own breakdown products.

Conclusions

These results highlight the potential of marine microbes and unrefined waste streams in circular, scalable bioplastic production. The present communication will discuss how these advances contribute to the development of novel, sustainable polymeric materials and open new pathways for integrating microbial biotechnology into polymer science.

Acknowledgments: Project TED2021-130211B-C31 funded by MCIN/AEI /10.13039/501100011033 and by the European Union NextGenerationEU/ PRTR