AUTHOR=Xiao Yue , Chen Xin , Lu Hang , Jiang Tingting , Wang Yichun , Liang Luyi , Dobretsov Sergey , Huang Yili 

TITLE=Regulation of quorum sensing activities by the stringent response gene rsh in sphingomonads is species-specific and culture condition dependent

JOURNAL=Frontiers in Microbiology

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2024.1368499

DOI=10.3389/fmicb.2024.1368499

ISSN=1664-302X

ABSTRACT=<p>Stringent response and quorum sensing (QS) are two essential mechanisms that control bacterial global metabolism for better survival. Sphingomonads are a clade of bacteria that survive successfully in diverse ecosystems. <italic>In silico</italic> survey indicated that 36 out of 79 investigated sphingomonads strains contained more than one <italic>luxI</italic> homolog, the gene responsible for the biosynthesis of QS signal acyl homoserine lactones (AHLs). Investigation of the regulatory effects of the stringent response gene <italic>rsh</italic> on QS related bioactivities were carried out using <italic>rsh</italic> mutants of <italic>Sphingobium japonicum</italic> UT26 and <italic>Sphingobium</italic> sp. SYK-6, both had three <italic>luxI</italic> homologs. Results indicated that deletion of <italic>rsh</italic> upregulated the overall production of AHLs and extracellular polymeric substances (EPS) in both UT26 and SYK-6 in rich medium, but affected expressions of these <italic>luxI/luxR</italic> homologs in different ways. In the poor medium (1% LB), <italic>rsh</italic> mutant of SYK-6 significantly lost AHLs production in broth cultivation but not in biofilm cultivation. The regulatory effects of <italic>rsh</italic> on QS activities were growth phase dependent in UT26 and culture condition dependent in SYK-6. Our results demonstrated the negative regulatory effect of <italic>rsh</italic> on QS activities in sphingomonads, which were very different from the positive effect found in sphingomonads containing only one <italic>luxI/R</italic> circuit. This study extends the current knowledge on the intricate networks between stringent response and QS system in sphingomonads, which would help to understand their survival advantage.</p>