The bacterial community (microbiome) of Arctic rivers, and of temperate rivers during winter, is of interest to ecologists and microbiologists as a unique collection of organisms adapted to psychrophilic (cold-growth) conditions.  We characterized these microbiomes by both culture-based and targeted unbiased metagenomic water sampling, identification, and taxonomic analysis of the bacteria from the Chesapeake Bay and Severn River (MD) in winter of 2020 and the Kuparuk River and Sagavanirktok River (AK) in summer 2019.  These analyses provide both breadth and depth to understanding of the microbial community in these watersheds, including comparisons between locations/conditions and geographic differences in bacterial taxa, and suggest that the headwater-origin hypothesis for river populations shown in other studies only partially explains development and structure of these microbiomes.  Preliminary analysis shows significant differences in taxonomic distribution by location independent of headwater origin, and potential links to the hydrology and/or geochemistry of the watersheds.  We are working to establish sampling and analysis programs for vertical year-over-year characterization of these microbiomes as well as further horizontal comparison between these watersheds.

The bacterial community (microbiome) of Arctic rivers, and of temperate rivers during winter, is of interest to ecologists and microbiologists as a unique collection of organisms adapted to psychrophilic (cold-growth) conditions.  We characterized these microbiomes by both culture-based and targeted unbiased metagenomic water sampling, identification, and taxonomic analysis of the bacteria from the Chesapeake Bay and Severn River (MD) in winter of 2020 and the Kuparuk River and Sagavanirktok River (AK) in summer 2019.  These analyses provide both breadth and depth to understanding of the microbial community in these watersheds, including comparisons between locations/conditions and geographic differences in bacterial taxa, and suggest that the headwater-origin hypothesis for river populations shown in other studies only partially explains development and structure of these microbiomes.  Preliminary analysis shows significant differences in taxonomic distribution by location independent of headwater origin, and potential links to the hydrology and/or geochemistry of the watersheds.  We are working to establish sampling and analysis programs for vertical year-over-year characterization of these microbiomes as well as further horizontal comparison between these watersheds.

Lipid A is a fundamental Gram-negative outer membrane component and the essential element of lipopolysaccharide (endotoxin), a potent immunostimulatory molecule. This work describes the metabolic adaptation of the lipid A acyl structure by Psychrobacter cryohalolentis at various temperatures in its facultative psychrophilic growth range, as characterized by MALDI-TOF MS and FAME GC-MS. It also presents the first elucidation of lipid A structure from the Colwellia genus, describing lipid A from strains of Colwellia hornerae and Colwellia piezophila, which were isolated as primary cultures from Arctic fast sea ice and identified by 16S rDNA sequencing. The Colwellia strains are obligate psychrophiles, with a growth range restricted to 15 °C or less. As such, these organisms have less need for fluidity adaptation in the acyl moiety of the outer membrane, and they do not display alterations in lipid A based on growth temperature. Both Psychrobacter and Colwellia make use of extensive single-methylene variation in the size of their lipid A molecules. Such single-carbon variations in acyl size were thought to be restricted to psychrotolerant (facultative) species, but its presence in these Colwellia species shows that odd-chain acyl units and a single-carbon variation in lipid A structure are present in obligate psychrophiles, as well. 

Lipid A is the essential component of endotoxin (Gram-negative lipopolysaccharide), a potent immunostimulatory compound. As the outer surface of the outer membrane, the details of lipid A structure are crucial not only to bacterial pathogenesis but also to membrane integrity. This work characterizes the structure of lipid A in two psychrophiles, Psychromonas marina and Psychrobacter cryohalolentis, and also two mesophiles to which they are related using MALDI-TOF MS and fatty acid methyl ester (FAME) GC-MS. P. marina lipid A is strikingly similar to that of Escherichia coli in organization and total acyl size, but incorporates an unusual doubly unsaturated tetradecadienoyl acyl residue. P. cryohalolentis also shows structural organization similar to a closely related mesophile, Acinetobacter baumannii, however it has generally shorter acyl constituents and shows many acyl variants differing by single methylene (-CH2-) units, a characteristic it shares with the one previously reported psychrotolerant lipid A structure. This work is the first detailed structural characterization of lipid A from an obligate psychrophile and the second from a psychrotolerant species. It reveals distinctive structural features of psychrophilic lipid A in comparison to that of related mesophiles which suggest constitutive adaptations to maintain outer membrane fluidity in cold environments.

Nghiem, S.V., Shepson, P.B., Simpson, W., Perovich, D.K., Sturm, M. Douglas, T., Rigor, I.G., Clemente-Colón, P., Burrows, J.P., Richter, A., Steffen, A., Staebler, R., Obrist, D., Moore, C., Bottenheim, J., Platt, U., Pöhler, D., General, S., Zielcke, J., Fuentes, J.D., Hall, D.K., Kaleschke, L., Woods, J., Hager, C., Smith, J., Sweet, C.R., Pratt, K., Custard, K., Peterson, P., Walsh, S., Gleason, E., Saiet, E., Webster, M., Lieb-Lappen, R., Linder, C., Neumann, G., Arctic Sea Ice Reduction and Tropospheric Chemical Processes, Bionature 2013, 4-8

Arctic sea ice extent reached another historical record low in summer 2012. More importantly, perennial sea ice extent in 2012 set the new record low in the long period that extends back to the last half of the 20th century as observed by a combination of long-term measurements acquired by ocean buoys and decadal data acquired by satellite scatterometers. To investigate impacts of sea ice reduction on atmospheric chemical processes, we conducted the BRomine, Ozone, and Mercury EXperiment (BROMEX) in March-April 2012 around Barrow, Alaska. We present an overview of BROMEX and highlight results to document sea ice change and chemical processes. We found a large number of bromine explosion events occurred in the BROMEX area where seasonal sea ice dominated.

The Gram-negative bacteria Yersinia pestis, causative agent of plague, is extremely virulent. One mechanism contributing to Y. pestis virulence is the presence of a type-three secretion system, which injects effector proteins, Yops, directly into immune cells of the infected host. One of these Yop proteins, YopJ, is proapoptotic and inhibits mammalian NF-κB and MAP-kinase signal transduction pathways. Although the molecular mechanism remained elusive for some time, recent work has shown that YopJ acts as a serine/threonine acetyl-transferase targeting MAP2 kinases. Using Drosophila as a model system, we find that YopJ inhibits one innate immune NF-κB signaling pathway (IMD) but not the other (Toll). In fact, we show YopJ mediated serine/threonine acetylation and inhibition of dTAK1, the critical MAP3 kinase in the IMD pathway. Acetylation of critical serine/threonine residues in the activation loop of Drosophila TAK1 blocks phosphorylation of the protein and subsequent kinase activation. In addition, studies in mammalian cells show similar modification and inhibition of hTAK1. These data present evidence that TAK1 is a target for YopJ-mediated inhibition.

Charles R. Sweet1, Courtney E. Chandler2, Caitlyn J. Koo1, Logan M. Treaster1, Timothy R. Brough1, Alexander J. Murray1,, Joseph P. Smith3, Shawn G. Gallaher3, Sophie M. Colston4, Ernst, R.K.2 

1 – U.S. Naval Academy (USNA) Chemistry Department, Annapolis, MD 21402, 2 – Department of Microbial Pathogenesis, School of Dentistry, University of Maryland, Baltimore, MD 21201 USA, 3 – U.S. Naval Academy (USNA) Oceanography Department, Annapolis, MD 21402, 4 – Center for BioMolecular Science & Engineering, US Naval Research Laboratory, Washington, DC, 20375

Brough, T.R.1,*, Murray, A.J.1,*, Barker, A.J.2, Smith, J.P.3, Douglas, T.A.2, Gallaher, S.G.3, Sweet, C.R.1,**

1 – U.S. Naval Academy (USNA) Chemistry Department, Annapolis, MD 21402, 2 – U.S. Army Corps of Engineers (USACE) Engineering Research & Development Center (ERDC) Cold Regions Research & Engineering Laboratory (CRREL), Fort Wainwright, AK 99703, 3 – U.S. Naval Academy (USNA) Oceanography Department, Annapolis, MD 21402

 Margaret M. Pana1, Natalie A. Lemek1, Rebecca E. Watson1, Andrew Keppel2, Joseph P. Smith2, Son V. Nghiem3, Charles R. Sweet1

1-Chemistry Dept, United States Naval Academy, Annapolis, MD USA, 2-Oceanography Dept, United States Naval Academy, Annapolis, MD USA, 3-Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA USA.