Marine bacteria often dominate the plankton biomass and are responsible for much of the cycling of organic matter, but bacterial diversity is poorly understood because conventional identification methods (requiring culturing) miss about 99% of the organisms. Recent advances permit characterization of microbial communities by analysis of 16S ribosomal RNA gene sequences directly from biomass without the need to culture the organisms; such studies from surface ocean samples have found only eubacteria, not archaebacteria (or Archaea), which are profoundly different. Here we report 16S rRNA sequences obtained from Pacific Ocean bacterioplankton samples collected from depths of 100 m and 500 m. Among these we found sequences only distantly related to those of any organisms previously characterized by 16S rRNA sequences, with similarities to the nearest such relatives (extreme thermophiles) approximately the same as those between animals and plants. We suggest that these sequences are from a previously undescribed archaebacterial group that may have diverged from the ancestors of characterized organisms very early in evolution.

Glucagon-like peptide 2 (GLP-2) is a 33-aa proglucagon-derived peptide produced by intestinal enteroendocrine cells. GLP-2 stimulates intestinal growth and upregulates villus height in the small intestine, concomitant with increased crypt cell proliferation and decreased enterocyte apoptosis. Moreover, GLP-2 prevents intestinal hypoplasia resulting from total parenteral nutrition. However, the mechanism underlying these actions has remained unclear. nM). GLP-2 analogs that activated GLP-2R signal transduction in vitro displayed intestinotrophic activity in vivo.These results strongly suggest that GLP-2, like glucagon and GLP-1, exerts its actions through a distinct and specific novel receptor expressed in its principal target tissue, the gastrointestinal tract.Glucagon-like peptides (GLPs) encoded by the proglucagon gene play key roles in glucose homeostasis, gastric emptying, insulin secretion, and appetite regulation (1). Glucagon and GLP-1 exert their effects through distinct G protein-coupled receptors (GPCRs). In contrast, unique receptors for GLP-2, glicentin, and oxyntomodulin have not yet been identified, despite considerable attempts at receptor isolation via classical molecular biology approaches (2). Recent studies have shown that GLP-2 is a potent intestinal growth factor that stimulates crypt cell proliferation and inhibits epithelial apoptosis (3). GLP-2 promotes epithelial proliferation in both small and large intestine; however, the mechanisms utilized by GLP-2 for promotion of intestinal growth remain unclear.To understand the mechanisms underlying GLP-2 action, we have carried out studies directed at the identification and cloning of the putative GLP-2 receptor. We now have isolated rat and human cDNAs encoding GLP-2-responsive GPCRs, which show highest similarity to receptors for glucagon and GLP-1. The GLP-2R is coupled to activation of adenylate cyclase, and the receptor is expressed selectively in rat hypothalamus and the gastrointestinal tract, known targets of GLP-2 action. These findings establish GLP-2 as a novel hormone that, like glucagon and GLP-1, exerts its actions through a distinct receptor expressed in a highly tissuerestricted manner. The GLP-2R should provide an important target for isolation of small molecules mimicking GLP-2 action and for future studies delineating specific mechanisms underlying GLP-2 action in the gut and central nervous system.

The extent of the diversity of marine prokaryotes is not well known, primarily because of poor cultivability. However, new techniques permit the characterization of such organisms without culturing, via 16S rRNA sequences obtained directly from biomass. We performed such an analysis by polymerase chain reaction amplification with universal primers on five oligotrophic open-ocean samples: from 100-m (three samples) and 500-m depths in the western California Current (Pacific Ocean) and from a 10-m depth in the Atlantic Ocean near Bermuda. Of 61 clones, 90% were in clusters of two or more related marine clones obtained by ourselves or others. We report 15 clones related to clone SAR 11 found earlier near Bermuda (S. J. Giovannoni, T. B. Britschgi, C. L. Moyer, and K. G. Field, Nature [London] 345:60-63, 1990), 11 related to marine cyanobacteria, 9 clustered in a group affiliated with gram-positive bacteria, 9 in an archaeal cluster we recently described (mostly from the 500-m sample), 4 in a novel 'y-proteobacterial cluster, and 6 in three two-membered clusters (including other archaea). One clone was related to flavobacteria. Only the cyanobacteria plus one other clone, related to Roseobacter denitrificans (formerly Erythrobacter longus Ochll4), were within 10% sequence identity to any previously sequenced cultured organism in a major data base. We never found more than two occurrences of the same sequence in a sample, although four times we found identical sequences between samples, two of which were between oceans; one of these sequences was also identical to SAR 11. Overall, the results point to broadly diverse microbial assemblages, with the common presence of heretofore phylogenetically undescribed groups.

The lipopolysaccharide (LPS) O-antigen side chains of Klebsiella serotype O1 have been studied by using mutants selected by resistance to a Klebsiella bacteriophage designated O1-A. Two classes of LPS mutants were identified. The major group (90%) synthesized rough LPS. The remaining 10% of the mutants produced a novel LPS profile that lacked the highest-molecular-weight O-substituted molecules (HMW-LPS) but still produced lower-molecular-weight O-substituted species (LMW-LPS). By using antisera raised against mutant Klebsiella strains and antiserum specific for Pasteurella haemolytica serotype 4, it was demonstrated that HMW-LPS and LMW-LPS contain shared epitopes. HMW-LPS also contained an epitope absent in LMW-LPS. This unique epitope was recognized by a monoclonal antibody (O1-52.6) and appears to be responsible for the serological cross-reaction between the O antigens of Klebsiella O1 and Escherichia coli O19. This HMW-LPS epitope was present in eight other Klebsiella O1 isolates which were examined. Electron microscopy demonstrated that HMW-LPS excluded overlying capsular polysaccharide for a distance of 25 to 40 nm. The distance was reduced to 10 to 18 nm in strains which synthesized only LMW-LPS and to zero in rough LPS strains. The HMW-LPS of Klebsiella O1 was shown to be an important virulence determinant, since this molecule was responsible for the resistance of the bacterium to nonspecific, complement-mediated serum killing.