In nature, bacteria often form heterogeneous communities enclosed in a complex matrix known as biofilms. This extracellular matrix, produced by the microorganisms themselves, serves as the first barrier between the cells and the environment. It is composed mainly of water, extracellular polymeric substances (EPS), lipids, proteins, and DNA. Cyanobacteria form biofilms and have unique characteristics such as oxygenic photosynthesis, nitrogen fixation, excellent adaptability to various abiotic stress conditions, and the ability to secrete a variety of metabolites and hormones. This work focused on the characterization of the cyanobacterium Halomicronema sp. strain isolated from a brackish environment. This study included microscopic imaging, determination of phenolic content and antioxidant capacity, identification of chemicals interfering with biofilm formation, and transcriptomic analysis by RNA sequencing and real-time PCR. Gene expression analysis was centered on genes related to the production of EPS and biofilm-related transcription factors. This study led to the identification of wza1 and wzt as EPS biomarkers and luxR-05665, along with genes belonging to the TetR/AcrR and LysR families, as potential biomarkers useful for studying and monitoring biofilm formation under different environmental conditions. Moreover, this work revealed that Halomicronema sp. can grow even in the presence of strong abiotic stresses, such as high salt, and has good antioxidant properties.