AUTHOR=Bondar Maryna , Pedro Filipa , Oliveira M. Conceição , da Fonseca M. Manuela R. , Cesário M. Teresa 

TITLE=Red algae industrial residues as a sustainable carbon platform for the co-production of poly-3-hydroxybutyrate and gluconic acid by Halomonas boliviensis

JOURNAL=Frontiers in Bioengineering and Biotechnology

VOLUME=Volume 10 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/bioengineering-and-biotechnology/articles/10.3389/fbioe.2022.934432

DOI=10.3389/fbioe.2022.934432

ISSN=2296-4185

ABSTRACT=<p>Polyhydroxyalkanoate (PHA) production using halophilic bacteria has been revisited because less severe operational conditions with respect to sterility can be applied, also alleviating production costs. <italic>Halomonas boliviensis</italic> was selected because it is a moderate halophile able to grow and attain high poly-3-hydroxybutyrate (P3HB) contents under 5–45 g/L NaCl concentrations, conditions that discourage microbial contamination. Industrial residues of the red alga <italic>Gelidium corneum</italic> after agar extraction were used as sugar platform to reduce costs associated with the carbon source. These residues still comprise a high carbohydrate content (30–40% w/w) of mainly cellulose, and their hydrolysates can be used as substrates for the bioproduction of value-added products. Preliminary assays using glucose were carried out to determine the best conditions for growth and P3HB production by <italic>H. boliviensis</italic> in bioreactor fed-batch cultivations. Two strategies were addressed, namely nitrogen or phosphorus limitation, to promote polymer accumulation. Similar P3HB cell contents of 50% (g<sub>polymer</sub>/g<sub>CDW</sub>) and yields <italic>Y</italic><sub><italic>P3HB/glucose</italic></sub> of 0.11–0.15 g <sub>polymer</sub>/g <sub>glucose</sub> were attained under both conditions. However, higher specific productivities were reached under P-limitation, and thus, this strategy was adopted in the subsequent study. Two organic acids, resulting from glucose metabolism, were identified to be gluconic and 2-oxoglutaric acid. Reducing the oxygen concentration in the cultivation medium to 5% sat was found to minimize organic acid production and enhance the yield of polymer on sugar to 0.20 g<sub>P3HB</sub>/g<sub>glucose</sub>. Finally, fed-batch cultivations using <italic>G. corneum</italic> hydrolysates as the only C-source achieved an overall volumetric productivity of 0.47 g/(L.h), 40% polymer accumulation, and negligible gluconic acid production.</p>