Production of Indole froml-Tryptophan and Effects of These Compounds on Biofilm Formation byFusobacterium nucleatumATCC 25586

Abstract

The L-tryptophan degradation product indole is a purported extracellular signaling molecule that influences biofilm formation in various bacteria. Here we analyzed the mechanisms of indole production in Fusobacterium nucleatum and the effects of tryptophan and indole on F. nucleatum planktonic and biofilm cells. The amino acid sequence deduced from the fn1943 gene in F. nucleatum ATCC 25586 was 28% identical to that deduced from tnaA in Escherichia coli, which encodes tryptophanase catalyzing the ␤-elimination of L-tryptophan to produce indole. The fn1943 gene was cotranscribed with the downstream gene fn1944, which is a homolog of tnaB encoding low-affinity tryptophan permease. The transcript started at position ؊68 or ؊153 from the first nucleotide of the fn1943 translation initiation codon. Real-time quantitative PCR showed that much more F. nucleatum fn1943 transcripts were obtained from log-phase cells than from stationary-phase cells. Indole production by the purified recombinant protein encoded by fn1943 was examined using highperformance liquid chromatography. The K m and k cat of the enzyme were 0.26 ؎ 0.03 mM and 0.74 ؎ 0.04 s ؊1 , respectively. F. nucleatum biofilm formation and the biofilm supernatant concentration of indole increased dose dependently with increasing tryptophan concentrations. Exogenous indole also increased F. nucleatum biofilm formation in a dose-dependent manner. Even at very high concentrations, tryptophan did not affect fn1943 expression, whereas similar indole concentrations decreased expression. Thus, exogenous tryptophan and indole were suggested to increase F. nucleatum biofilms.

Indole Affects Biofilm Formation in Bacteria

“…It is corresponded by recent studies on Vibrio cholerae, which show indole activating genes involved in vibrio polysaccharide (VPS) production (essential for V. cholerae biofilm formation), influencing the expression of genes involved in motility, protozoan grazing resistance, iron utilization, and ion transport [42]. Exogenous tryptophan and indole are also suggested to increase Fusobacterium nucleatum biofilms [43]. Moreover, even P. aeruginosa that can not synthesize indole, is able to respond to this molecule (e.g., in diminishing virulence, enhancing biofilm formation and antibiotic resistance) and degrades it rapidly [44].…”

Indole inhibits bacterial quorum sensing signal transmission by interfering with quorum sensing regulator folding

“…Many bacteria have the trp operon, where indole is a precursor for tryptophan biosynthesis (Sasaki-Imamura et al, 2010;Yanofsky, 2007). In P. putida, this trp operon was significantly induced by indole .…”

ELUCIDATING THE ROLE OF METABOLITES AS QUORUM SENSING SIGNALS USING PHASE PLANE ANALYSIS: THE CASE OF INDOLE IN ESCHERICHIA COLI

“…Also, indole contributes to low resistance to environmental stresses (antibiotics, low pH and alcohol), but it does not show a significant effect on biofilm formation. 16 On the other hand, in Gram-negative bacteria Vibrio Cholerae 17 and Fusobacterium nucleatum 18 indole can enhance biofilm formation in a dosedependent manner. These results and the current study suggest that the action of indole on cells' metabolic state is an adaptation to different environment conditions.…”