Optimizing the Production of Polyhydroxyalkanoates and Other Biotechnological Products by Halophilic Archaea Isolated from Qatari Extreme Environment

Abstract

Plastic pollution is a major global concern, posing severe threats to environmental sustainability and human health. Global plastic production has reached approximately 450 million tons annually, yet only about 9% is effectively managed. The accumulation of unmanaged plastic waste has become a serious environmental burden, emphasizing the urgent need for eco-friendly and biodegradable alternatives, such as bioplastics. Among the diverse biological sources explored for sustainable bioplastic production, halophilic archaea have emerged as highly promising candidates due to their robustness and ability to thrive under extreme conditions. In this study, we investigated the potential of an indigenous archaeal isolate, Halostagnicola larsenii L1QC2, obtained from a hypersaline Qatari environment, for bioplastic production. The isolated archaeal strain exhibited pronounced halotolerance and thermotolerance, confirming its strong adaptability to extreme environmental conditions and its potential for industrial biotechnological applications. Morphological characterization by SEM- EDX revealed a homogeneous and compact cell structure with a smooth surface, indicative of efficient PHB accumulation within the cells. FTIR spectroscopy confirmed the presence of characteristic functional groups corresponding to poly(3- hydroxybutyrate) (PHB), while thermogravimetric analysis (TGA) demonstrated its high thermal stability. The polymer exhibited an overall degradation between 143 °C and 520 °C, maintaining stability up to approximately 350 °C, with a total weight loss of 95.7%. Cultivation in glucose-based medium resulted in a relatively slow growth rate (0.175 ± 0.027 day⁻¹) and steady PHB accumulation from day 2 to day 6, reaching 11% of dry cell weight. To enhance sustainability and reduce production costs, food waste-based media containing 4000 ppm and 8000 ppm TOC were utilized, which markedly increased the growth rates to 0.485 and 0.599 day⁻¹, respectively. The corresponding doubling time decreased to 1.43 days, and PHB accumulation doubled, reaching 22% of dry cell weight. Scaling up the fermentation process further improved both growth performance and polymer yield; however, additional optimization of fermentation parameters remains necessary to maximize PHB productivity and process efficiency.