Genetic characterization of a novel Salinicola salarius isolate applied for the bioconversion of agro-industrial wastes into polyhydroxybutyrate

Abstract

Background PHB is of significant concern due to its potential applications as green alternatives to traditional petrochemical-based plastics. In the present study, a new strain of Salinicola salarius, a halophilic bacterium, was isolated from the New Suez Canal in Egypt and characterized exclusively as a potential PHB producer. Further analysis of the ES021 genome was conducted to identify and elucidate the genes involved in PHB production. Results Different PHB-producing marine bacteria were isolated from the New Suez Canal and characterized as PHB producers. Among the 17 bacterial isolates, Salinicola salarius ES021 strain showed the capability to accumulate the highest amount of PHB. Whole genome analysis was implemented to identify the PHB-related genes in Salinicola salarius ES021 strain. Putative genes were identified that can function as phaCAB genes to produce PHB in this strain. These genes include fadA, fabG, and P3W43_16340 (encoding acyl-CoA thioesterase II) for PHB production from glucose. For PHB production from fatty acids, phaJ and fadB are involved. Environmental factors such as aeration and incubation temperature were optimized to attain high productivity of PHB. The results showed that growing Salinicola salarius ES021 strain at 30°C on a shaker incubator (110 rpm) for 48 h resulted in the highest PHB productivity. To maximize PHB production, different raw materials i.e., salted whey and molasses were examined as cheap carbon sources. The PHB productivity was increased two-fold (13.34 g/l) when using molasses (5% sucrose) as a fermentation media. This molasses medium was used to upscale PHB production in a 20 L stirred-tank bioreactor yielding a biomass of 25.12 g/l, and PHB of 12.88 g/l. Furthermore, the produced polymer was confirmed as PHB using Fourier-transform infrared spectroscopy (FTIR) and Gas chromatography-mass spectroscopy (GC-MS) analysis. Conclusions Herein, Salinicola salarius ES021 strain was demonstrated as a high natural producer of PHB from agro-industrial wastes. A detailed genome characterization of the ES021 strain showing the PHB-related genes was presented in this study. However, further metabolic engineering is required to confirm the gene networks required for PHB production in this strain.