**3. Control agents related to HABs**

Studies have been carried out to find a better way of controlling HABs. Different biotic factors have been identified to mitigate the option of HABs. Where use of different bacteria was done to tone down HABs in coastal and freshwater community [21].

## **4. Toxins**

The most toxic algal strain is *M. aeruginosa,* which constantly produces microcystins, acts harmful to aquatic organisms as well as to humans. Were microcystins have been reported as tumor-promoting [22]. Some bacteria mainly acts

antagonistic towards Cyanobacteria and are predatory bacteria, some other acts as toxin-degrading. Were Predatory helps to make an environmentally pleasant solution to available HABs. Also number of prey–predator and the mechanism of Cyanobacterial lysis, were some effectual biological control approach [23]. Few of Cyanobacteria mitigated using the secretion of *Cyanobacteriolytic* substances by some *Bacillus* Sp. typically *Bacillus cereus* and [24], *S. neyagawaensis* [25], *Streptomyces* [26], *Pseudomonas fluorescens* species [27]. *Pedobacter* Sp*.* secretes some mucus-like secretion as self-defense against *M. aeruginosa*. *Raoultella* Sp. removes *M. aeruginosa* by dissolving microbial metabolites and humic acid [28]. *Agrobacterium vitis* use Quorum sensing to lyse *M. aerugenosa* [29]. *Sandaracinobactor sibiricus, Methylobacterium zatmanii* and *Rhizobium* Sp. use lytic mechanism to remove *M. aeruginosa* [30]. Some *Bacillus* Sp. use cell-to-cell contact mechanism and production of an extracellular product to remove *Aphanizomenon flos-aquae* [31] and *M. aeruginosa* [32, 33]. Several reports suggested that algal viruses often existed at stable numbers, even when their hosts were absent [34]. With claim of that summer and spring season showing the eminent decay of cultivated viruses succeeding to four-seasons of analysis [35]. The regular seasonal study also noticed that the stumpy decay of algal virus during the wintry weather that permitted for the survival of about 126 continues days under the ice-cover in the freezing freshwater pond [36]. These agents show high specificity and high efficiency, but it gain limited attention due to high cost, as also requires upscaled level experiment confirmation [37].
