Influence of different organic nitrogen sources on antimicrobial activity of Pseudoalteromonas sp

Background: The objective of this work was study the influence of different nitrogen substrates on the growth and antimicrobial activity of a marine strain of Pseudoalteromonas sp. (Ps), which is an antimicrobial producer. Methods: In order to assess the effect of organic nitrogen source on a marine bacterium, culture media containing different concentrations of soy peptone, yeast extract, malt extract, casein or mixtures of them were prepared. The organic nitrogen substrates were used as the sole carbon and nitrogen sources and, additionally, the amino nitrogen value of each of the culture media was estimated. Their effects were evaluated by spectrophotometry and disc diffusion methodology using S. aureus and P. aeruginosa strains as target. Results: The results showed maximum production of antimicrobial activity against S.aureus MRSA and P aeruginosa in YPC culture medium. In ASB medium there was good antimicrobial activity in spite of low bacterial growth. Conversely, null antimicrobial activity was registered when the marine bacteria were cultured in YMG medium. A low concentration of peptone or yeast extract in the culture medium stimulated antimicrobial activity, but increasing the concentration of nitrogen in the medium induced significant reductions in antimicrobial activity against S. aureus and complete inhibition/repression against P. aeruginosa, while casein did not stimulate antimicrobial activity at any concentration tested. Conclusions: Bacterial growth and antimicrobial activity production by Pseudoalteromonas sp. depend on the amino nitrogen concentration in the medium. However, casein substrate slightly stimulates cell growth but does not stimulate the antimicrobial activity of this marine bacterium. Thus, the choice of medium to produce antimicrobial compounds against S. aureus MRSA and P. aeruginosa can influence the fermentation process.