## 4 Discussion
[43] proved that cyanobacteria that grow in red light contain a higher concentration of phycocyanin than cyanobacteria grown in white light. In our case, it is most likely that exposure of cyanobacteria to a red-light laser resulted in an increase in the phycocyanin content. This particular pigment has antimicrobial activity against pathogenic bacteria [43]. This may account for the increase in the antimicrobial activity after exposure to a red-light laser. _Synechococcus elongatus_ was isolated from rice field water. _S. elongatus_ is a unicellular rod-shaped cyanobacterium [44]. _S. elongatus_ forms biofilms with extracellular polymeric materials, and these give _S. elongatus_ the ability to resist environmental stress and antimicrobial drugs [45]. Extracts of _S. elongatus_ showed antimicrobial effects before and after laser treatment. Similarly, Ref. [46] proved the _Synechococcus genus_ can be considered as a source of bioactive compounds against bacteria. Metabolic extracts of _S. elongatus_ showed antimicrobial activity against several strains of bacterial species [14]. With regard to the molecular basis of bioactive compound production from cyanobacteria in general and _Synchococcus_ sp. in particular, [PERSON] et al. [47] recommended the use of in silico alongside in vivo screening for antimicrobial compounds from cyanobacteria. Indeed, [PERSON] et al. [48] screened marine cyanobacteria associated with sponge and found that three marine _Sychococcus_ sp. have polyktetide synthase genetic systems. Nonetheless, [PERSON] et al. [5] reported that strains of _Synechococcus_ sp. lack non-ribosomal peptide synthetase and polyktetide synthase genetic systems. This suggests that the presence or absence of those systems is strain-dependent. Strains of the same species differ in the presence or absence of those systems, and this may explain the ability of some strains of the same species to have antimicrobial activity while others do not. Indeed, [PERSON] et al. [48] showed that _Synechococcus_ sp. 0715 had no antimicrobial activity against _Straphylococcus aureus_, whereas strain 0815 of the same species had antimicrobial activity. Moreover, [PERSON] et al. [48] also showed that the _Leptotho spongobia_1115 strain had both a non-ribosomal peptide synthetase system as well as a polyketide synthase genetic system and was effective against StaphylococcusGeneus. On the other hand, _Leptohoe spongobia_1105 only had a polyketide synthase genetic system and did not show antimicrobial bioactivity against _Staphylococcus aureus_. Therefore, more studies need to be carried out to further explore the molecular machinery of antimicrobial biosynthesis within cyanobacteria. No studies are available on the effect of laser on those systems. Nonetheless, with regard to radiation in general, a study that involved _Synechococcus elongatus_, according to ([[https://www.osti.gov/servlets/purl/1367105](https://www.osti.gov/servlets/purl/1367105)]([https://www.osti.gov/servlets/purl/1367105](https://www.osti.gov/servlets/purl/1367105)), accessed 20 April 2022), showed that cyanobacteria may undergo changes to resist ionizing radiation, such as an increase in genome copy number (being polyploidy, overexpression of reactive oxygen species' degradation enzymatic system and condensed nucleotide structure). A study on _Synechococcus lividus_ demonstrated that low doses of ionizing radiation stimulated cell proliferation as a result of peroxide-degrading enzymes and glucose catabolism [49]. [PERSON] et al. [50] showed that nitric oxide alleviates oxidative damage induced by enhanced ultraviolet-B radiation in a cyanobacterium. [PERSON] et al. [51] reviewed the effects of UV-B radiation on cyanobacteria; it can induce damage on cellular DNA and directly interacts with certain biomolecules that absorb in the UV range. It can also cause indirect effects through inducing oxidative stress exerted by the reactive oxygen species generated. [PERSON] et al.