AUTHOR=Xiong Rui , Liu Yuyang , Pu Jieying , Liu Jianping , Zheng Dexiang , Zeng Jianming , Chen Cha , Lu Yang , Huang Bin 

TITLE=Indole Inhibits IncP-1 Conjugation System Mainly Through Promoting korA and korB Expression

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.628133

DOI=10.3389/fmicb.2021.628133

ISSN=1664-302X

ABSTRACT=<p>Indole works as an interspecies signal molecule to regulate multiple physiological activities, like antibiotic resistance, acid resistance, and virulence. However, the effect of indole on conjugation is unknown. Here, with <italic>Escherichia coli SM10</italic>λπ as a donor strain that carries a chromosomally integrated conjugative RP4 plasmid, we explored the effect of indole on conjugation of a mobilizable pUCP24T plasmid imparting gentamycin resistance. The results showed that exogenous indole treatment inhibited conjugative transfer of pUCP24T from <italic>SM10</italic>λπ to recipient strains, <italic>Pseudomonas aeruginosa PAO1</italic> and <italic>E. coli EC600</italic>. Furthermore, raising endogenous indole production through overexpression of TnaA, a tryptophanase, in <italic>SM10</italic>λπ significantly inhibited both <italic>SM10</italic>λπ-<italic>PAO1</italic> and <italic>SM10</italic>λπ-<italic>EC600</italic> conjugation, whereas deficiency of <italic>tnaA</italic> reversed the phenotype. Subsequent mechanistic studies revealed that exogenous indole significantly inhibited the expression of mating pair formation gene (<italic>trbB</italic>) and the DNA transfer and replication gene (<italic>trfA</italic>), mainly due to the promotion of regulatory genes (<italic>korA</italic> and <italic>korB</italic>), and the result was confirmed in <italic>tnaA</italic> knockout and overexpression strains. Additionally, we found that both extracellular indole production and <italic>tnaA</italic> expression of <italic>SM10</italic>λπ were downregulated by ciprofloxacin (CIP). Intriguingly, one-eighth minimum inhibitory concentration of CIP treatment clearly facilitated both <italic>SM10</italic>λπ-<italic>PAO1</italic> and <italic>SM10</italic>λπ-<italic>EC600</italic> conjugation, and indole inhibited CIP-induced conjugation frequency. These data suggest that indole may play a negative role in the process of CIP-induced conjugation. This is the first study to reveal the biological function of indole-inhibiting conjugation and its role in CIP-induced conjugation, which may be developed into a new way of controlling the spread of antibiotic resistance.</p>