Study design

We designed this study to evaluate the ability of mammalian PRRs to detect deep-sea bacteria via the PAMP, LPS. Therefore, we cultured bacterial strains from the deep sea of PIPA to screen in a flow cytometry–based assay for their ability to interact with endogenous murine PRRs, CD14 and TLR4. Our results indicated that 80% of live bacteria strains did not engage with murine CD14 and/or TLR4 and were categorized as silent to these PRRs. To confirm that LPS from deep-sea bacteria was silent, we purified LPS from stimulatory and silent Moritella strains to characterize the downstream innate immune response to extracellular and intracellular LPS in murine and human cells. LPS from Moritella strains that were silent to murine and human PRRs did not initiate any downstream innate immune response. LPS from silent Moritella strains also did not engage with murine PRRs in vivo or in L. polyphemus. We then hydrolyzed and purified lipid A from Moritella LPS and confirmed that the activity of silent LPS was a direct result of the structure of the lipid A moiety. To delineate the differences between stimulatory and silent Moritella lipid A, we characterized the structure of lipid A and sequenced the genomes of each strain of interest.