## 1 Background  
Cyanobacteria are a rich source of bioactive compounds with various antimicrobial activities [1; 2; 3]. These bioactive compounds are mostly produced during secondary growth. Secondary metabolism is mainly concerned with the production of molecules that have biological effects but are not necessary for growth or reproduction. Instead, they allow cyanobacteria to survive under different stresses. In addition, they play a role in treating and preventing several forms of diseases, including fungal, viral, and bacterial diseases [4]. With regard to the molecular basis of production of bioactive compounds,including antimicrobials, [PERSON] et al. [5] reported that this is mainly related to genes responsible for the synthesis of the non-ribosomal peptide synthetases (NRPSs) and polyketide synthases (PKSs) but they are not the only genetic systems for bioactive compound production. Strains of _Cyanothece_ sp. strain WH8904 and _Lyngbya_ sp. strain PCC7419, for example, do not have those typical genetic systems but still produce bioactive compounds. The bioactive compounds produced by cyanobacteria depend on the culture conditions and growth phase. Therefore, manipulation of physical and biochemical factors would allow for the production of bioactive compounds from cyanobacteria [6; 7]. The most important factors include physical factors, such as the incubation period and the pH of the culture media [8], as well as biochemical factors, such as the culture nutrient composition [9]. Cyanobacterial extracts are known for their antibacterial action against a wide array of bacteria. Extracts of _Phormidium_ species inhibited the growth of pathogenic strains of _Pseudomonas aeruginosa_, _Staphylococcus aureus_, _Escherichia coli_, and _Streptococcus enteritidis_[10]. An organic acetone extract of _Oscillatoria agardtii_ was highly active against _Salmonella sentenberg_[11]. Ethanol extracts of _Spirulina platensis_ demonstrated antimicrobial activity against different species of Gram-negative and Gram-positive bacteria [12]. Ethanol and aqueous extracts of _Anabaena circinalis_ showed antibacterial activity against _Serratia marcescens_ and _Escherichia coli_. Additionally, _Nostoc commune_ and _Nostoc muscorum_ exhibited antimicrobial activity [13]. Organic extracts of different species of phytoplankton also inhibited the growth of different species of bacteria [14]. Interestingly, the antimicrobial bioactivity of cyanobacterial extracts was increased significantly with the use of UV and gamma irradiation of the cyanobacterial cells [15]. Additionally, the antimicrobial bioactivity of extracts directly exposed to UV irradiation was increased as well [16]. However, the laser irradiation effect on the antimicrobial bioactivity has never been investigated. Laser is an abbreviation for \"light amplification by the stimulated emission of radiation\" and is non-ionizing radiation. Laser discharge mainly occurs in the ultraviolet, visible light, and infrared frequencies, depending on the wavelength generated [17]. A laser is a gadget that excites molecules or atoms to release light at specific frequencies and intensify that light, essentially creating an exceptionally focused light emission [18]. In biological cells, the penetration and absorption of laser radiation depends on several factors, such as the distance from the laser beam to the cell, the area of the cell exposed to the laser radiation, laser wavelength, dose, and power _2.5_. density. The dose and power density are calculated from the following formulas [19]: dose (J) = mean power \(\times\) treatment time; and power density for continuous output laser (mW/cm\({}^{2}\)) = mean power/spot size sample. A low-energy laser has been found to modify several biological processes in cell cultures and animal models [20]. At the cellular level, laser irradiation can cause important biological effects, such as cellular reproduction, collagen synthesis, and emission of growth factor from cells [21].