Diverse Profiles of AI-1 Type Quorum Sensing Molecules in Cultivable Bacteria from the Mangrove (Kandelia obovata) Rhizosphere Environment

Abstract

Mangrove rhizosphere environment harbors diverse populations of microbes, and some evidence showed that rhizobacteria behavior was regulated by quorum sensing (QS). Investigating the diverse profiles of QS molecules in mangrove ecosystems may shed light on the bacterial roles and lead to a better understanding of the symbiotic interactions between plants and microbes. The aims of the current study focus on identifying AI-1 type QS signals, i.e., acyl homoserine lactones (AHLs), in Kandelia obovata rhizosphere environment. Approximately 1200 rhizobacteria were screened and 184 strains (15.3%) tested were positive. Subsequent 16s rRNA gene sequencing and dereplication analyses identified 24 species from the positive isolates, which were affiliated to three different phyla, including Proteobacteria, Firmicutes, and Actinobacteria. Thin-layer chromatography separation of extracts revealed diverse AHL profiles and detected at least one active compound in the supernatant of these 24 cultivable AHL-producers. The active extracts from these bacterial isolates were further evaluated by ultra performance liquid chromatography-mass spectrometry, and the carbon side chain length ranged from C4 to C14. This is the first report on the diversity of AI-1 type auto-inducers in the mangrove plant K. obovata, and it is imperative to expand our knowledge of plant-bacteria interactions with respect to the maintenance of wetland ecosystem health.

Novel Quorum Sensing Activity in East Antarctic Soil Bacteria

“…This is not surprising given that LuxI/LuxR-based QS is common within Proteobacteria, and hence is able to make full use of this communication system. The highest production of presumptive HSLs in Proteobacterial isolates was also reported in another study (38), compared to members of Actinobacteria and Firmicutes, which are relatively unfamiliar with this language. Despite the relatively high number of potential HSLs produced by Novosphingobium sp.…”

“…Active compounds detected in the cultures of gram-positive bacteria ranged from C6 to C11-HSLs, with no evidence of the short chain C4-HSL. Gram-positive bacteria that were identified as potential HSL-producers from previous studies (36–38), also produced medium to long chain length active compounds ranging from C8 to C14-HSLs, albeit the non-alkaline pH of their respective environmental setting, except for one Actinobacterium isolated from a hypersaline microbial mat, which was found to produce C4-HSL (39). These findings may indicate gram-positive bacteria, if capable of producing HSLs, are not in favour of short-chain HSLs, or these compounds could be produced in concentrations ineffective for standard bioassays.…”

“…Surprisingly, within all bacterial isolates displaying active compound production, 15 were gram-positive bacteria spanning Actinobacteria and Firmicutes (Table 1). While HSL-based QS is common in gram-negative Proteobacteria (74), to our best knowledge, there are only four known reports of this QS system in gram-positive bacteria, two of which were of marine origin (36, 37), one was from mangrove rhizospheres (38) and one isolated from microbial mats (39). All the potential HSL producers isolated from these studies were also affiliated to either the Actinobacteria or Firmicutes phylum.…”

“…While the LuxI/LuxR system was previously thought to be exclusive to gram-negative bacteria, knowledge on the distribution of this QS system among microbes is growing, with HSL activity now reported in Archaea (33–35), in gram-positive marine bacteria (36, 37), gram-positive rhizobacteria from a mangrove swamp (38) and gram-positive bacteria from hypersaline microbial mats (39). In Antarctica, a limited number of HSL-based QS studies is being restricted to marine environments (24, 40).…”

Opportunistic bacteria use quorum sensing to disturb coral symbiotic communities and mediate the occurrence of coral bleaching

“…), which are middle‐ to long‐chain signalling molecules. Possible reasons for producing long‐chain AHL molecules are as an ecological strategy to avoid degradation (Ma et al ., ,b) and act as a regulator of coral‐associated bacteria to adapt the changeable environment (Peixoto et al . ).…”