eng Oriental Scientific Publishing Company Biomedical and Pharmacology Journal 0974-6242 2025-09-30 18 3 2315 2326 10.13005/bpj/3258 67635 article Nuha Khalid Neyazi 1 Hend Maarof Tag 2 Naglaa Elshafey 4 Nashwa Hagagy 5 Department of Biology, College of Science and Arts at Khulis, University of Jeddah, Jeddah, Saudi Arabia Department of Nursing, College of Applied Medical Sciences, University of Jeddah, Jeddah, Saudi Arabia Department of Zoology, Faculty of Sciences, Suez Canal University, Egypt Botany and Microbiology Department, Faculty of Science, Arish University, Al-Arish, Egypt Botany and Microbiology Department, Faculty of Science, Suez Canal University, Ismailia, Egypt Biodegradable polyhydroxyalkanoates (PHAs), consisting of monomers and heteropolymers, this is an alternative for polymers generated by fossil fuels. Halophilic archaea produced polyhydroxyalkanoates (PHAs) as intracellular granules reserves energy in response to nutrients scarcity. Nevertheless, there is a scarcity of comprehensive understanding of these processes and the capacity of halophilic archaea to accumulate PHAs. This study focused on isolation of haloarchaea from Saudi Arabia's Red Sea solar saltern and investigate their growth and synthesis of polyhydroxybutyrate (PHB) under varying pH levels, temperatures, and NaCl concentrations. In addition, the study aimed to assess the accumulation of polyhydroxybutyrate (PHB) under nutrient-limited conditions utilizing cost-effective sources of carbon, like carboxymethyl cellulose (CMC), glycerol, glucose, starch and sucrose. Identification of candidate strains was achieved via 16S rRNA genome sequencing. Subsequently, the sequences were added to the NCBI GenBank and given accession numbers OQ366239-OQ366242.Haloferax sp. strain HSM17 produced the greatest quantity of PHB (50.94%) when starch was the only source of carbon. The best growth was shown at 65°C, a pH 7, and 10% salinity. The chemical combination of the biopolymer was evaluated by applying GC-MS. Hemolysis was then measured to determine the cytotoxicity of the extracted PHB towards red blood cells. The results showed a considerable decrease in damage to human red blood cells parallel to the positive control (P<0.05). Haloferax sp. strain HSM17 has great potential as a producer of polyhydroxybutyrate (PHB) using cheap carbon sources. https://biomedpharmajournal.org/vol18no3/biopolymer-polyhydroxybutrates-production-from-promising-haloarchaea-characterization-optimization-with-in-vitro-cytotoxic-activity/ Biodegradable materials Cytotoxic assays Extremophiles Halophilic archaea Microbial biopolymers Saltern ecosystems