Diversity analysis of phytase-producing bacteria from coastal seawater and sediment and characterization of their phytases

Phytic acid, also known as inositol hexaphosphate (IP6), is one of the most abundant organophosphorus compounds in nature. Its degradation by phytase plays a key role in the natural phosphorus cycle. In addition, phytases are widely used in livestock and poultry feed to enhance phosphorus utilization. While most reported and commercial phytases are derived from terrestrial organisms, relatively few originate from marine microorganisms, and information on the diversity of phytase-producing marine bacteria remains limited. In this study, following enrichment with sodium phytate, we analyzed the bacterial diversity in seawater and sediment samples collected from the coast of Aoshan Bay in Qingdao, China, using 16S rRNA gene amplicon sequencing. A total of 138 OTUs representing 10 phyla, 15 classes, 37 orders, 55 families, and 70 genera were identified. Furthermore, 27 phytase-producing bacterial strains were isolated from the enrichment cultures, primarily belonging to the phyla Firmicutes (14/27) and Proteobacteria (12/27). Five extracellular phytase genes were identified through genome sequencing of three representative strains. These phytases were subsequently expressed and characterized. All were classified as histidine acid phosphatase-type phytases, exhibiting optimal activity at temperatures of 50–60 °C and pH values of 4.0–5.0. Notably, phytase 3919 showed a specific activity as high as 2485.25 U/mg, indicating strong potential for practical applications. This study provides insight into the diversity of coastal bacteria involved in phytic acid degradation, contributing to our understanding of bacterial-driven phosphorus cycling in coastal ecosystems and facilitating the discovery of phytases with industrial potential.