The complete nos region essential for dissimilatory nitrous oxide reduction by the endosymbiotic diazotroph Rhizobium meliloti was identified in a cosmid (pYC7) carrying a 10.1-kb EcoRI fragment of the nod megaplasmid. This gene region was localized by Southern hybridization and Tn5 mutagenesis to within 8 kb downstream from the fixGHIS cluster. Nucleotide sequence determination of a 4.6-kb DNA segment including the structural gene nosZ and its flanking regions showed sequence homology and similarity in genetic organization with the nosRZDFY genes of Pseudomonas stutzeri Zobell. The genes were arranged in three complementation groups, comprising the nosZ structural gene, the nosR regulatory gene, and the nosDFY copper-processing genes. The derived amino acid sequence of the R. meliloti nosZ product (a multi-copper nitrous oxide reductase) was more similar to those of the analogous gene products of Paracoccus and Pseudomonas species than to that of Alcaligenes eutrophus. The nosZ gene was preceded by nosR, which encodes a regulatory protein containing C-terminal cysteine clusters similar to those present in the 4Fe-4S binding region of bacterial ferredoxins. The nosDFY genes, located downstream from nosZ, were identified as copper-processing genes encoding a periplasmic protein, an ATP/GTP-binding protein, and a membrane protein, presumably forming a copper-processing system. A consensus sequence for an Anr-or Fnr-binding site similar to that in the upstream sequence of nosZ in Paracoccus denitrificans or P. stutzeri was absent in R. meliloti. No rpoN-binding site preceding the nos genes was detected, and none of the Tn5 insertions in the nos gene region affected symbiotic N 2 -fixing ability.
Four freshwater Antarctic lakes were examined for the presence of pgalactosidase-producing bacteria using mineral medium enrichments and lactose. Enrichments from only one of the lakes produced growth and two strains were isolated that were very similar in phenotype and fatty acid profile, and shared considerable homology in their DNA (DNA-DNA hybridization = 9327 YO). The strains were psychrotrophic with theoretical T,,,,,, Tmin and To,, of 30-31, -7 O and 26 "C, respectively. The P-galactosidase in cell extracts had an optimal activity at 39 "C. The strains were Gram-negative rods, showed gliding motility, contained branched and hydroxy fatty acids, and menaquinone 6 as the major respiratory quinone. The strains did not form microcysts and utilized lactose while using ammonium ions as a source of nitrogen, and a range of other sugars. The G+C content of the DNA was 34 mol%. Phylogenetic analysis of one of the strains, by comparison of 165 rDNA sequences, showed that it was most similar, but not identical to, Flavobacterium columnare and [Sporocytophaga] cauliformis '. Both species could be differentiated phenotypically from the Antarctic isolates. DNA-DNA hybridization of the Antarctic isolate with six different members of the Flavobacterium 165 rDNA cluster showed no strain with greater than 18% relatedness. The nearest type species to the Antarctic isolate in the phylogenetic analysis was Flavobacterium aquatile. The name Flavobacterium hibernum is proposed for the Antarctic strains, and the type strain is ATCC 51468T (= ACAM 376T).Keywords: Flavobacterium hibernum, psychrotroph, P-galactosidase, Antarctica INTRODUCTIONMany humans are intolerant to lactose in their diet and as a result are unable to consume unfermented dairy products without considerable discomfort. One technological approach to solving this problem is to use bgalactosidase in the processing of dairy foods. However, the optimal temperatures for hydrolysis of lactose by P-galactosidases range between 30 and 40 OC, which is also the ideal temperature range for the growth of mesophiles that contaminate and spoil dairy products (Gounot, 1991). Hydrolysis of lactose at low temperatures may be a viable option if a psychrophile can be isolated that produces an efficient low-temperature b-galactosidase (Gounot, 199 1).As part of an ongoing study on the microbial diversity of Antarctic ecosystems, and due to the possible benefits arising from the isolation of psychrophilic j?-galactosidase-producing strains, we targeted lactoseutilizing strains from a number of freshwater Antarctic lakes for enrichment and isolation. A taxonomic study of the isolates was undertaken and the work is herein described. Isolation of bacterial strains. Four freshwater Antarctic lakes [conductivity (pS cm-') and pH given in parentheses after each name] : Druzhby Lake (29,7*2), Crooked Lake (26,7.1), Pauk Lake (118, 7-0) and Lichen Lake (73, 7.3), were sampled for lactose-utilizing bacteria. Each lake was sampled twice, at the same hour from sample points within 10 m of each...
From the MeOH extract of Pseudopterogorgia elisabethae, collected from the Bahamas, four new diterpenes, elisabethin E (1), elisabethin F (2), pseudopterosin P (3), and pseudopterosin Q (4), were isolated and their structures established with the aid of extensive spectroscopic studies. Compounds 3 and 4 showed antibacterial activity selectively against the Gram-positive bacteria Streptococcus pyogenes, Staphylococcus aureus, and Enterococcus faecalis.
From the MeOH extract of Pseudopterogorgia elisabethae, collected from the Bahamas, four new diterpenes, elisabethin E (1), elisabethin F (2), pseudopterosin P (3), and pseudopterosin Q (4), were isolated and their structures established with the aid of extensive spectroscopic studies. Compounds 3 and 4 showed antibacterial activity selectively against the Gram‐positive bacteria Streptococcus pyogenes, Staphylococcus aureus, and Enterococcus faecalis.
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