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Oligoribonuclease (Orn) is a 3' to 5' exonuclease that degrades nanoRNAs, which can serve as primers for transcription initiation at a significant fraction of promoters. One of Orn's substrates, pGpG inhibits the enzymatic activity of EAL-domain containing phosphodiesterases (PDEs), thereby increasing intracellular cyclic-di-GMP (c-di-GMP) level. Here, we found that an orn mutant of Pseudomonas aeruginosa displayed reduced cytotoxicity, which was mainly due to deficient type III secretion system (T3SS). Given the importance of T3SS in pathogenicity, we examined the bacterial virulence in a mouse acute pneumonia model and found that the Δorn mutant was highly attenuated compared to the wild type PA14 strain. Overexpression of an EAL domain-containing PDE reduced the c-di-GMP level as well as biofilm formation in the Δorn mutant. However, no effect was observed on the expression of T3SS genes, suggesting that increased c-di-GMP level is not the solely cause of defective T3SS in the Δorn mutant. Overall, our results demonstrated an essential role of Orn in the expression of T3SS as well as pathogenesis of P. aeruginosa.

The compositions of glycerol dialkyl glycerol tetraethers (GDGTs) in surface sediments and sediment cores from the Eastern Lau Spreading Center (ELSC), South Pacific Ocean, were determined. Isoprenoid GDGTs (isoGDGTs) and branched GDGTs (brGDGTs) are present in all the samples, with archaea and bacteria, respectively, as the sources of these membrane lipids. Greater concentrations of isoGDGTs (0.08–38.0 ng/g dry weight (dw)) than brGDGTs (0.05–27.4 ng/g dw) indicate that archaea made larger contributions to the GDGT pool in the ELSC sediments than bacteria. The relative abundance of brGDGTs and BIT index (the branched vs. isoprenoid tetraether) values are higher in samples taken from the seafloor in the vicinity of or close to hydrothermal vents than in samples taken distant from hydrothermal activity, suggesting that brGDGTs are likely produced in the ELSC hydrothermal vents. Temperature estimates based on TEX 86 (TetraEther indeX of tetraethers consisting of 86 carbon atoms) appear to reflect local surface water temperatures despite potential in situ hydrothermal input of GDGTs to the ELSC sediments.