International Journal of Advanced Engineering Research and Science (IJAERS) [Vol-6, Issue-7, Jul- 2019] https://dx.doi.org/10.22161/ijaers.6732 ISSN: 2349-6495(P) | 2456-1908(O) www.ijaers.com Page | 267 Activity of two Exometabolites produced by Escherichia coli on the Synthesis of Pyocyanin Ray Ravilly Alves Arruda 1 , Bianca Teixeira Morais de Oliveira 1 , Tarcísio Tárcio Corrêa Bonifácio 1 , Vinícius Cavalcante Morais 1 , Ian Porto Gurgel do Amaral 2 , Ulrich Vasconcelos 1 1 Laboratório de Microbiologia Ambiental, Centro de Biotecnologia, Universidade Federal da Paraíba, João Pessoa-PB, Brazil 2 Laboratório de Biotecnologia de Organismos Aquáticos, Centro de Biotecnologia, Universidade Federal da Paraíba, João Pessoa, Brazil Abstract — The secretion of metabolites with antimicrobial activity is one of the strategies employed by bacteria to respond to negative stimuli promoted during interspecies competition. In a long-term stationary phase. Pseudomonas aeruginosa and Escherichia coli can synthesize diffusible exometabolites whose action is to mutually inhibit the exposed cells, guaranteeing the balance of both populations in a certain site. The P. aeruginosa may have an advantage in that it produces pyocyanin. However, the excretion of indole and acetate by E. coli may reduce this advantage. This work aims to detect the influence of different concentrations of these two exometabolites on the synthesis of pyocyanin in two wild isolates of P. aeruginosa. After incubation under shaking for 72 h at 29°C, reduction of up to 50% of the concentration of pyocyanin in the presence of indole was observed. On the other hand, no change was observed in the production of the pigment with the acetate, alone or when in combination with concentrations of less than 0.5 mM indole. It reduced the inhibitory effect of the compound, reflecting an increase in pyocyanin production of more than 20%. The results contribute to help understanding the ecological mechanisms of competition between the two species. Keywords— Pseudomonas aeruginosa, Natural phenazine, Microbial antagonism, Indole, Anti-Quorum Sensing molecules. I. INTRODUCTION The In natural environments, different bacterial species coexist, forming complex multicellular communities that collectively respond to stimuli from the environment they inhabit, resulting in the stability of their populations [1]. During a long-term stationary phase, competition for space and nutrients is a natural process that occurs in mixed microbial populations, where a given microorganism produces certain diffusible substances whose function is to inhibit the growth of a second microorganism. These substances can be of various natures, for example enzymes, organic acids or phenazine compounds, among them, pyocyanin [2]. Pyocyanin is a bright blue pigment, characteristic of the P. aeruginosa species. It is also the main pigment synthesized by fluorescent pseudomonads [3]. In addition, pyocyanin is known as one of the most important virulence factors of P. aeruginosa. In addition to the role of a signaling molecule in cell-dependent cell density phenomena [4], it has been reported to participate in events involving resistance to antibiotics [5], inflammatory processes [6] and competition with other microorganisms at a given site [7]. In aqueous media, the relationship between P. aeruginosa and E. coli reveals certain particularities during a long-term stationary phase. Both organisms can synthesize diffusible exometabolites whose action is to mutually inhibit the exposed cells, ensuring the balance of both populations at a given site [8]. In addition to pyocyanin, other important exometabolites have been identified in P. aeruginosa , such as proteases, hemolysins, rhamnolipids and pyoverdine, a green color pigment that also has a siderophore function [9]. In an attempt to overcome the pressures exerted by P. aeruginosa, as well as its exponent metabolic advantage, E. coli strains can release into the environment, for example, acetate and indole. The first is formed as a by- product in aerobiosis when the absorption rate of the primary carbon source is greater than its conversion to biomass and CO2 [10]. On the other hand, indole is formed from the metabolism of tryptophan [11] and concentrations of 0.5 to 1 mM can regulate E. coli responses to stresses exerted by the environment, including competition with P. aeruginosa [12]. The microbial interspecies relationships are a subject with a number of aspects that can be explored. The