alvei. Similar to E. coli, the addition of glucose and glycerol (0.5%) in LB medium completely abolished the production of indole in P. alvei for 36 h, while lactose (0.5%) did not affect indole accumulation (Figure 1B). This result suggested that the indole accumulation in P. selleck alvei
was strictly controlled by catabolic repression although transport mechanisms of glucose and glycerol would be different. In other words, P. alvei did not produce indole in the presence of the preferred carbon sources such as glucose and glycerol. Unlike the current observation, it was previously reported that the tryptophanase in B. alvei (renamed as P. alvei) appeared to be constitutive, and catabolite repression was not operative . The report studied the effect of only tryptophan on tryptophanase activity and found that the activity of P. alvei tryptophanase was independent of tryptophan . Indole inhibits the heat-resistant cell CA3 in vivo numbers of P. alvei The main hypothesis of this study was that a large quantity of extracellular indole would play a quorum sensing role in cell physiology of P. alvei so we investigated the effect of indole on sporulation and biofilm formation which was influenced by cell population and environmental stresses in other Bacillus DNA Synthesis inhibitor strains . In P. alvei, the addition of exogenous indole (0, 0.2, or 1.0 mM) surprisingly
decreases the heat-resistant colony-forming unit (CFU) in a dose dependent manner (Figure 2A). For example, indole (1 mM) decreased the heat-resistant CFU of P. alvei compared
to no addition of indole 51-fold at 16 hr (0.26 ± 0.01% vs.13.2 ± 0.9%) and 10-fold at 30 hr (8 ± 6% vs. 77 ± 10%). To confirm the presence of exogenous indole, the indole level in DSM medium was measured with HPLC. The level of exogenous indole (1 mM) was not changed at all over 24 h (data not shown). Hence, the exogenous indole was not utilized as a carbon source and inhibited the heat-resistant CFU of P. alvei. Figure 2 Effect of indole and 3-indolylacetonitrile on the heat-resistant CFU of P. alvei. The cells (an initial turbidity Ribonucleotide reductase of 0.05 at 600 nm) were grown in spore forming DSM medium for 16 h and 30 h. Exogenous indole (A) and 3-indolylacetonitrile (B) were added at the beginning of the culture to test the effect of indole (Ind) and 3-indolylacetonitrile (IAN) on the heat-resistant CFU. Lysozyme-resistance assays (C) were performed with 30 h-grown cells with and without indole and 3-indolyacetonitrile, and lysozyme (1 mg/mL) was treated for 20 min. Each experiment was repeated three to four times and one standard deviation is shown. Additionally, the temperature effect of indole on the heat resistance of P. alvei was investigated since the environmental temperature affected indole signaling in E. coli . Unlike in E. coli, the inhibitory effect of indole (1 mM) on the heat-resistant CFU of P. alvei at 30°C (0.3 ± 0.1% vs.