Quorum Sensing in a Methane-Oxidizing Bacterium

Abstract

Aerobic methanotrophic bacteria use methane as their sole source of carbon and energy and serve as a major sink for the potent greenhouse gas methane in freshwater ecosystems. Dissecting the molecular details of how these organisms interact in the environment may increase our understanding of how they perform this important ecological role. Many bacterial species use quorum sensing (QS) systems to regulate gene expression in a cell density-dependent manner. We have identified a QS system in the genome of Methylobacter tundripaludum, a dominant methane oxidizer in methane enrichments of sediment from Lake Washington (Seattle, WA). We determined that M. tundripaludum produces primarily N-3-hydroxydecanoyl-L-homoserine lactone (3-OH-C 10 -HSL) and that its production is governed by a positive feedback loop. We then further characterized this system by determining which genes are regulated by QS in this methane oxidizer using transcriptome sequencing (RNA-seq) and discovered that this system regulates the expression of a putative nonribosomal peptide synthetase biosynthetic gene cluster. Finally, we detected an extracellular factor that is produced by M. tundripaludum in a QS-dependent manner. These results identify and characterize a mode of cellular communication in an aerobic methane-oxidizing bacterium.IMPORTANCE Aerobic methanotrophs are critical for sequestering carbon from the potent greenhouse gas methane in the environment, yet the mechanistic details of chemical interactions in methane-oxidizing bacterial communities are not well understood. Understanding these interactions is important in order to maintain, and potentially optimize, the functional potential of the bacteria that perform this vital ecosystem function. In this work, we identify a quorum sensing system in the aerobic methanotroph Methylobacter tundripaludum and use both chemical and genetic methods to characterize this system at the molecular level.KEYWORDS methane, methanotroph, quorum sensing, sociomicrobiology, acyl-homoserine lactone, biosynthetic gene cluster A erobic methane-oxidizing bacteria (methanotrophs) are an important component of the carbon cycle that serve to sequester carbon from the potent greenhouse gas methane after it is produced by anaerobic microbial ecosystems (1, 2). Methanotrophs provide a carbon and energy source for communities of organisms that cannot oxidize methane themselves, thereby serving as key supporting species in the environment (3, 4). The methanotroph Methylobacter tundripaludum is a member of the Gammaproteobacteria (type I methanotroph), and it has been repeatedly identified as a dominant member of methane enrichment and stable isotope probing experiments of sediment from Lake Washington, Seattle, WA (3, 5-7). Methylobacter spp. have also been isolated from other geographically distinct regions, including the arctic (8), estuaries (9), and temperate wetlands (10), highlighting the diverse environments inhabited by this genus. We, therefore, use M. tundripaludum as part of a model system for ...

A Complex Interplay between Nitric Oxide, Quorum Sensing, and the Unique Secondary Metabolite Tundrenone Constitutes the Hypoxia Response in Methylobacter

“…The former mutant does not produce the signal molecule HSL, which induces the transcription of the genes essential for the biosynthesis of Tun. Thus, this mutant produces neither HSL nor Tun under the conditions used (29). The latter mutant does not produce Tun, while it still produces HSL (30).…”

“…5). It has been noted previously that in the MbaI mutant not producing native HSL, when exogenous HSL was added, some of the most downregulated genes were the genes for Hcp and Hcr (29). Thus, it appears that the Hcp/Hcr and the QS/Tun systems are inversely regulated and that they potentially regulate each other.…”

“…A total of 16 RNA samples were sequenced, representing the wild type and the Hcp mutant incubated under the four conditions, in two replicates each (Table S3). When the transcriptomes of the Hcp mutant and the wild type were compared, under either condition, the most dramatic response to the lack of Hcp was manifested by the recently characterized gene cluster encoding quorum sensing (QS) functions and the novel secondary metabolite tundrenone (Tun) (29) (Fig. 4).…”

“…Transcriptomics experiment 4 was designed to further decipher the potentially interlinked roles of Hcp/Hcr and QS/Tun in the hypoxia response. This experiment was carried out with the previously described mutants in QS (MbaI) (29) and Tun biosynthesis (TunJ) (30). The former mutant does not produce the signal molecule HSL, which induces the transcription of the genes essential for the biosynthesis of Tun.…”

Light assisted antibiotics

“…In the human skin, free radical generation exhibits high efficiency for wavelengths around 303 nm (UVB range) and 355 nm (UVA range) [49]. Recently, a product with strong absorbance at 297nm was reported by Puri et al [50] as present in Methylobacter tundripaludum supernatants in a quorum sensing dependent manner. The collected product was reported to have no distinguishable growth inhibitory activity against E.coli MG 1655 or Bacillus subtilis PY79 , however, a possible growth inhibitory action of the product was not excluded for other bacterial species.…”