Screening of a soil tyrosianse producing Microbacteria sp. strain HM24 and Comparison of its Tyrosinase activity in different mediums containing natural sources of L-tyrosine. Microbacterium sp. HM24

Tyrosinases are important biological enzymes with various applications, including the breakdown of phenolic compounds and melanin production. L-tyrosine, as the primary substrate for the enzyme tyrosinase, is naturally present in various natural sources. Actinobacterias are one of the good tyrosinase producing candidates in nature.In this study, we investigated tyrosinase-producing actinobacterial strains and assessed the enzyme's activity in a superior strain. For this purpose, a suitable soil sample was isolated from a specific depth in the Langar, Kerman, Iran, where actinobacteria were abundant. These actinobacterial strains were cultured on Gause medium and identified based on their morphology, pigment production, and Gram staining. Subsequently, the strains were transferred to a culture medium containing L-tyrosine to investigate their tyrosinase-producing capabilities. Best strain was selected by observing the formation of dark-colored colonies, indicative of tyrosinase activity. Finally, the 16S rRNA gene was used to identify this strain. It was then cultured in media containing natural L-tyrosine to assess its tyrosinase enzyme activity for potential substrate selection .Considering that one of the activities of the tyrosinase enzyme is pigment production, the SPF and antioxidant properties of the produced brown pigment were investigated in Tyrosine Agar. Bacterial strains with powdery and rough morphologies were isolated after culturing the soil sample on a Gause medium.Twenty strains displaying filamentous growth and Gram-positive characteristics were isolated from the soil sample.These strains were transferred to a tyrosine agar to investigate their tyrosinase production.The strain with a dark-brown color was selected for genome sequencing.BLAST analysis revealed that HM24 belongs to the genus Micrococcus with 99.97% identity. HM24 was inoculated in four different media containing various L-tyrosine sources The tyrosinase activity across these substrates was compared. Peanut and soybean meal were identified as simple and accessible substrates for activating the tyrosinase enzyme. The produced pigment exhibited an SPF of 134.36, making it suitable for sunscreen products and demonstrated 69% DPPH reduction, comparable to other reported biopigments.