## 3 Discussion  
Human pathogenic bacteria, _A. baumaniii_, methicillin-resistant _S. aureus_, and _P. aeruginosa_ bacteria, are antibiotic-resistant microorganisms for which the development of research for the discovery of new antibacterial drugs have become crucial. To date, only a small number of marine bacteria have been studied for bioactive bVOCs [24]. This study aimed to determine the antibacterial activity of the volatilome produced by marine bacteria, _Bacillus_ sp. BO53 and _Pseudoalteromonas_ sp. GA327, isolated from octocords. Overall, the VOCs produced by _Pseudoalteromonas_ sp. GA327 lead to the inhibition of the two Gram-negative pathogenic bacteria investigated at early stages (24 h) when compared to the antibacterial activity of _Bacillus_ sp. BO53. The antibacterial activity of _Bacillus_ sp. BO53 VOCs against _P. aeruginosa_ was higher  
Figure 2: Molecular structure of _Bacillus_ sp. BO53 and _Pseudoalteromonas_ sp. GA327. detected volatile compounds. (**a**) VOCs detected on _Bacillus_ sp. BO53 and _Pseudoalteromonas_ sp. GA327: (1) 2-butanone, (2) 1-pentanol, (3) p-cpynene, (4) 3-methylacetophenone, (5) 2-nonanone, (**b**) VOCs detected only on _Bacillus_ sp. BO53: (6) 2,2,4-trimethylpentane, (7) 0-xylene, (8) 5-acetyl-2-methylpyridine, (9) \(\alpha\)-cubebene, (10) 1-decanol, (11) logicyclene, (**c**) VOCs detected only on _Pseudoalteromonas_ sp. GA327: (12) 2-butanone, (13) 2-pentanone, (14) butyl formate, (15) 2-heptanone, (16) 6-methyl-5-heptene-2-one, (17) benzyl alcohol, (18) 2-decanone, (19) 2-undecanone. than for _A. baumannii_ and _S. aureus_, and lead to a total inhibition of _P. aeruginosa_ growth within 48 h after exposure to the _Bacillus_ sp. BO53 VOCs. The HS-SPME-GC-MS analysis, lead to the identification of ketones, mainly 5-acetyl-2-methylpyridine, as the most abundant volatile compound produced by _Bacillus_ sp. BO53. Among the main VOCs biosynthesized by bacteria are ketones and alcohols [25]. It is evident from this research that the volatile compound 5-acetyl-2-methylpyridine leads to the growth reduction of _A. baumannii_, _S. aureus_, and the inhibition of _P. aeruginosa_. In this sense, pyridine derivatives have shown relevant bioactivity against Gram-positive and Gram-negative bacteria [26]. The antibacterial activity of this volatile compound has to be performed to corroborate its bioactivity. On the other hand, studies have reported a relevant inhibitory activity of 2-butanone upon _S. aureus_, _P. aeruginosa_, and _E. coli_[27]. Furthermore, [PERSON] et al. [28] have reported an important growth inhibition of _S. aureus_ and _E. coli_ by 2-nonanone. The alcohol volatile compound 1-undecanol, which was determined as one of the main compounds produced by _Bacillus_ sp. BO53 inhibits _S. aureus_ by damaging the bacterial cell membrane [29]. This reported bioactivity also might contribute to the growth reduction of methicillin-resistant _S. aureus_ observed in the current study. The lack of complete inhibition of _S. aureus_ and _A. baumannii_ strains can be attributed to the low amount of VOCs produced by _Bacillus_ sp. BO53, which was due to its low growth rates. The results of this investigation have revealed an effective antibacterial activity of _Pseudoalteromonas_ sp. GA327 VOCs on _A. baumannii_ and _P. aeruginosa_ strains. These observations suggest that alcohol, ketone, and ester volatile compounds, which were the most abundant VOCs identified from _Pseudoalteromonas_ sp. GA327, generate an efficient inhibitory biochemical mechanism on the Gram-negative bacteria studied. 1-Pentanol and benzyl alcohol, which were detected in high amounts in _Pseudoalteromonas_ sp. GA327, affect the bacterial cell membrane, causing fluidization or interrupting the functions of the membrane proteins. The alteration of the bacterial membrane due to volatile alcohols allows other antimicrobial compounds to easily penetrate the cell membrane [30] 2-Butanone was the main antibacterial ketone identified from _Pseudoalteromonas_ sp. GA327.