Abstract
It is known that some bacteria, especially members of the family Rhizobiaceae, have multiple N-acyl homoserine lactones (AHL) synthase genes and produce multiple AHL signals. However, how bacteria selectively utilize these multiple genes and signals to cope with changing environments is poorly understood. Ensifer adhaerens is an important microorganism in terms of biotechnology, ecology and evolutionary. In this study, we investigated the AHL-based QS system of E. adhaerens X097 and its response to different lifestyles or nutrients. Draft genome sequence data indicated that X097 harbored three distinct AHL synthase genes (ensI1, 2, 3) and seven luxR homologs, which was different from other E. adhaerens strains. In vitro expression indicated that plasmid-encoded ensI1 and ensI2 directed production of multiple AHLs, while chromosome-encoded ensI3 only directed production of C14-HSL. Predicted three dimensional structure of EnsI3 was quite different from that of EnsI1 and EnsI2. X097 produced different AHL profiles in Luria-Bertani (LB) and NFB medium, under biofilm and planktonic lifestyle, respectively. Notably, expression of ensI1 and ensI2 but not ensI3 is hypersensitive to different lifestyles and nutrients. The hypersensitive response of plasmid-encoded AHL synthase genes to different culture conditions may shed a light on the phylogenetic development of AHL synthase genes in Rhizobiaceae family.
Highlights
Quorum sensing (QS) is a cell density-dependent communication system in bacteria (Asfahl and Schuster, 2017)
Hypersensitive Plasmid-Encoded acyl homoserine lactones (AHL) Synthase Gene observed within the family Rhizobiaceae, which corresponded to the Rhizobium/Agrobacterium and Shinella/Ensifer groups
It is known that quite a few bacteria produce multiple AHLs, and possess multiple AHL synthase genes (Sanchez-Contreras et al, 2007; Huang et al, 2009)
Summary
Quorum sensing (QS) is a cell density-dependent communication system in bacteria (Asfahl and Schuster, 2017). N-acyl homoserine lactones (AHLs)-based QS system is quite common among bacteria belonging to the Rhizobiaceae family, wherein many strains represent some of the best studied QS model organisms, such as Agrobacterium tumefaciens, Rhizobium leguminosarum, Rhizobium etli, and Sinorhizobium meliloti (Wisniewski-Dyé and Downie, 2002; Marketon et al, 2003; White and Winans, 2007). The type species of the Ensifer genus, Ensifer adhaerens, was an outlier in the latter group which separated from the rest of the Ensifer strains (Ormeño-Orrillo et al, 2015). This emphasizes the distinctive taxonomical status of E. adhaerens. AHL-producing E. adhaerens has never been mentioned in previous studies until we found its prevalence in freshwater biofilm, soil and plant rhizosphere in our recent works (Huang et al, 2012, 2013a; Zeng et al, 2014)
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