Indole as an intercellular signal in microbial communities

Abstract

Bacteria can utilize signal molecules to coordinate their behavior to survive in dynamic multispecies communities. Indole is widespread in the natural environment, as a variety of both Gram-positive and Gram-negative bacteria (to date, 85 species) produce large quantities of indole. Although it has been known for over 100 years that many bacteria produce indole, the real biological roles of this molecule are only now beginning to be unveiled. As an intercellular signal molecule, indole controls diverse aspects of bacterial physiology, such as spore formation, plasmid stability, drug resistance, biofilm formation, and virulence in indole-producing bacteria. In contrast, many non-indole-producing bacteria, plants and animals produce diverse oxygenases which may interfere with indole signaling. It appears indole plays an important role in bacterial physiology, ecological balance, and possibly human health. Here we discuss our current knowledge and perspectives on indole signaling.

Efficacy of 7‐benzyloxyindole and other halogenated indoles to inhibit Candida albicans biofilm and hyphal formation

“…In Pseudomonas putida , signalling molecules such as indole enhances TtgGHI efflux pump that are relevant for antibiotic resistance (Molina‐Santiago et al ., 2014). The previous studies have reported that indole inhibits biofilm formation and suppresses the virulence of bacterial strains such as Staphylococcus aureus , Agrobacterium tumefaciens (Lee and Lee, 2010; Lee et al ., 2013, 2015a,b; Lee et al ., 2016) and Vibrio cholera (Mueller et al ., 2009). Likewise, indole derivatives such as 7‐fluoroindole, 7‐hydroxyindole, 3‐indolyl acetonitrile and 2‐aminobenzimidazoles have been reported to exhibit antimicrobial activities against pathogenic bacteria (Lee et al ., 2009, 2011, 2012, 2015a,b; Frei et al ., 2012).…”

Indole-3-acetic acid: A widespread physiological code in interactions of fungi with other organisms

“…The auxin acts as an effector molecule between IAA-producing bacteria and plants, and bacteria -bacteria interactions have been discussed in several reviews. 3,4,14,15 However, IAA biosynthetic pathways and the role of IAA in fungal ecology have not been widely investigated. 6,16,17 In this review, we address the aforementioned issues.…”

Isolation of Indole Utilizing Bacteria Arthrobacter sp. and Alcaligenes sp. From Livestock Waste

“…Indole is the metabolic product of tryptophan generated by tryptophanase enzymatic activity encoded by tnaA gene in E. coli [1]. It is also produced by bacteria in the rumen and many living systems as a product of tryptophan metabolism.…”

“…Various industries that synthesize pharmaceuticals, cosmetics, pesticides, disinfectants, agrochemicals, and dyes are also considered sources of indole [2]. There are more than 85 Gram-positive and Gram-negative bacterial species that yield indole as the product of tryptophan metabolism [1]. Biochemical and molecular studies have shown that indole plays various roles in bacterial systems, for example, as an extracellular signal [1,3], for multicopy plasmid maintenance [4], cell division, biofilm formation [5], and acid and drug resistance [5][6][7][8].…”

“…There are more than 85 Gram-positive and Gram-negative bacterial species that yield indole as the product of tryptophan metabolism [1]. Biochemical and molecular studies have shown that indole plays various roles in bacterial systems, for example, as an extracellular signal [1,3], for multicopy plasmid maintenance [4], cell division, biofilm formation [5], and acid and drug resistance [5][6][7][8]. In addition, indole also controls the virulence of several pathogenic bacteria [7] and it has multifaceted properties and applications in prokaryotic systems [9][10][11] as well as eukaryotic systems [12].…”