Production and Characterization of Bioplastic by Polyhydroxybutyrate Accumulating Erythrobacter aquimaris Isolated from Mangrove Rhizosphere

Abstract

The synthesis of bioplastic from marine microbes has a great attendance in the realm of biotechnological applications for sustainable eco-management. This study aims to isolate novel strains of poly-β-hydroxybutyrate (PHB)-producing bacteria from the mangrove rhizosphere, Red Sea, Saudi Arabia, and to characterize the extracted polymer. The efficient marine bacterial isolates were identified by the phylogenetic analysis of the 16S rRNA genes as Tamlana crocina, Bacillus aquimaris, Erythrobacter aquimaris, and Halomonas halophila. The optimization of PHB accumulation by E. aquimaris was achieved at 120 h, pH 8.0, 35 °C, and 2% NaCl, using glucose and peptone as the best carbon and nitrogen sources at a C:N ratio of 9.2:1. The characterization of the extracted biopolymer by Fourier-transform infrared spectroscopy (FTIR), Nuclear magnetic resonance (NMR), and Gas chromatography-mass spectrometry (GC-MS) proves the presence of hydroxyl, methyl, methylene, methine, and ester carbonyl groups, as well as derivative products of butanoic acid, that confirmed the structure of the polymer as PHB. This is the first report on E. aquimaris as a PHB producer, which promoted the hypothesis that marine rhizospheric bacteria were a new area of research for the production of biopolymers of commercial value.

Bioplastic (poly-3-hydroxybutyrate) production by the marine bacterium Pseudodonghicola xiamenensis through date syrup valorization and structural assessment of the biopolymer

“…accumulated 55.6, 51.6, 37.4 and 25% PHB using sugar cane bagasse, corn cob, teff straw, and banana peel as carbon sources 43 . Moreover, marine Saccharococcus thermophilus 33 and V. harveyi 14 had maximum PHB yields of 0.701 g/L and 1•2 g/L based on dry cell weight, respectively, after 72 h. Additionally, high PHB production (7.3 g/L) was achieved at 120 h by E. aquimaris 22 . Extending the fermentation period reduced PHB production, which can be explained by an explicit positive relation between PHB production and bacterial biomass, where both decreased as carbon was consumed, resulting in the exhaustion of PHB 31,42 in addition to decaying enzyme activity for PHB biosynthesis 40 .…”

“…In the present study, marine bacterial strains were isolated from the Al-Madhaya coast of the Red Sea in the southern region of Saudi Arabia. The PHB-producing Erythrobacter aquimaris was isolated from the mangrove rhizosphere of this site 22 . Fewer isolates were obtained from the seawater samples than from the sediment samples, probably because the prevalent environmental conditions and rainy season diluted the water 31,32 .…”

“…This species is a slightly halophilic bacterium belonging to the phylum Proteobacteria, a predominant bacterial phylum in marine habitats 37 . Marine ecosystems such as the Red Sea 13,22 promote diverse biopolymer-producing microbes, which can synthesize unique genes and enzymes 17 . The marine bacteria producing PHB that were identified as Ralstonia, Pseudomonas sp., Bacillus sp., and Vibrio proteolyticus based on 16S rRNA were isolated from marine environments 15 .…”

“…The marine bacteria producing PHB that were identified as Ralstonia, Pseudomonas sp., Bacillus sp., and Vibrio proteolyticus based on 16S rRNA were isolated from marine environments 15 . Several new bacterial strains producing high amounts of PHB were isolated from various marine environments and have been identified by analyzing 16S rRNA sequences, including bacteria from the mangrove rhizosphere (Bacillus thuringiensis, Erythrobacter aquimaris) 13,22 , sediments (Vibrio sp.) 5,38 , surface seawater (Alteromonas lipolytica) 39 , the tunicate Phallusia nigra (V. harveyi MCCB 284) 14 , and sponges (Bacillus megaterium) 24 The variation in microbial communities in marine habitats may be affected by pollution, as seawater can become rich in organic and inorganic nutrients.…”

“…Indeed, the different types of bacterial communities in the Red Sea are reported to be a source of potentially useful bioproducts for biotechnological and pharmaceutical applications, and the gene responsible for PHB synthase exhibits relatively high abundance in the microorganisms living in the Red Sea 19 . The marine bacterial species Vibrio harveyi 14 , Paracoccus species, Micrococcus species 21 , Erythrobacter aquimaris 22 , Halomonas elongata 23 , Bacillus megaterium 24 , Cupriavidus necator 25 , and Haloferax mediterrani 26 have been found to be potent producers of bioplastics. Consequently, Red Sea habitats are regarded as a potential source for novel bacterial strains that exhibit efficient PHB production.…”