# Evaluating Soil Bacteria for the Development of New Biopreparations with Agricultural Applications
## 4 Discussion
subtilis_ has demonstrated antimicrobial activity against a broad range of pathogens, including _Saccharicola_, _Cochliobolus_, _Alternaria_, _Fusarium_ spp., and _Ralstonia solanacarum_[80; 81; 82]. The findings of the present study, in which _B. subtilis_ exhibited the largest growth-inhibition zones against several pathogens, align well with those reported previously. _B. licheniformis_ also exhibited significant antimicrobial activity, which is supported by its ability to produce a diverse array of antimicrobial substances, such as bacteriocins, peptides, proteins, and cyclic lipopeptides. Studies have shown that this strain effectively inhibits pathogens such as _R. solani_, _Sclerotium rofsii_, _Fusarium_ _culumorum_, _Pythium_ spp., _Alternaria alternata_, and _Phoma medicaginis_[83; 84]. Fermentation supernatants of _B. licheniformis_ TG116 have demonstrated efficacy against a variety of phytopathogens [85]. In this study, _B. licheniformis_ displayed significant antifungal activity, particularly against _R. solani_ and _F. graminearum_. The antimicrobial properties of _B. velezensis_ are also well-documented, with strains exhibiting substantial activity against phytopathogens such as _F. graminearum_[86; 87] and _F. oxysporum_[88]. Additionally, _B. velezensis_ has demonstrated activity against _Phytophthora sojae_ and _R. solanacarum_[89]. Genomic analyses have underscored the biocontrol potential of _B. velezensis_, revealing the presence of antimicrobial biosynthetic gene clusters [90]. In this study, _B. velezensis_ exhibited consistent and robust inhibitory effects, particularly against _Fusarium_ sp. and _P. exigua. P. amylolyticus_ has also been reported to possess antimicrobial activity, producing non-ribosomal peptides and polyketides that target a range of phytopathogens [91]. Previous studies have shown _Peanibacillus_ sp. efficacy in inhibiting notable pathogens such as _F. oxysporum_ and _R. solani_[92]. The results of the present study confirm these findings, as _P. amylolyticus_ displayed substantial antimicrobial activity against three tested phytopathogens (_Fusarium_ sp.) but not against _R. solani. P. megaterium_ exhibited comparatively lower antimicrobial activity than the other strains. However, previous reports have noted its effectiveness against pathogens such as _F. culmorum_ and _F. graminearum_[93], as well as against _Agrobacteriumium tumefaciens_, _Erwinia carotovora_, and _R. solanacarum_[94]. While its activity in this study was limited, _P. megaterium_ may still hold potential for specific biocontrol applications under different conditions or against different phytopathogens. The alignment of these findings with existing literature underscores the antimicrobial potential of the selected bacterial strains against diverse phytopathogens. Particularly high broad-spectrum activity was demonstrated by _B. licheniformis_, _B. subtilis_, and _B. velezensis_. These results highlight their potential applicability as biocontrol agents, contributing to sustainable agricultural practices and the management of plant diseases. Our study is in the first to investigate the cytotoxicity of soil bacterial metabolites on an insect cell model, Sf-9. _B. licheniformis_ and _B. subtilis_ metabolites have been previously shown to have cytotoxic effects towards various human and mammalian cell lines, including embryonic kidney (HEK293), ovary Chinese hamster (CHO-K1), colon cancer Caco-2, breast cancer MDA-MB-231, prostate cancer PC-3, lung cancer NCI-H23, stomach cancer NUGC-3, and renal cancer ACH [95; 96; 97; 98]. The cytotoxic metabolites of _B. licheniformis_ and _B. subtilis_ include small cyclic lipopeptide lichenysin A, linear lipopeptide gageostatin, catecholate siderophore bacillibactin, macrolactin A, and enediyne [97; 98; 99; 100; 101]. The _B. subtilis_and _B. licheniformis_ strains used in the present study could probably be applied in biopreparations for the control of insect pathogens. However, more research is needed into their metabolites and biological properties.