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In Vitro Analyses, Animal Models, and 60 Clinical Cases of Invasive Aspergillus terreus Infection. William J. Steinbach, 2004. Contribution of SAR11 Bacteria to Dissolved Dimethylsulfoniopropionate and Amino Acid Uptake in the North Atlantic Ocean. Rex R. Malmstrom, 2004.SAR11 bacteria are abundant in marine environments, often accounting for 35% of total prokaryotes in the surface ocean, but little is known about their involvement in marine biogeochemical cycles . Previous studies reported that SAR11 bacteria are very small and potentially have few ribosomes, indicating that SAR11 bacteria could have low metabolic activities and could play a smaller role in the flux of dissolved organic matter than suggested by their abundance . To determine the ecological activity of SAR11 bacteria, we used a combination of microautoradiography and fluorescence in situ hybridization (Micro-FISH) to measure assimilation of 3H-amino acids and [35S]dimethylsulfoniopropionate (DMSP) by SAR11 bacteria in the coastal North Atlantic Ocean and the Sargasso Sea . We found that SAR11 bacteria were often abundant in surface waters, accounting for 25% of all prokaryotes on average . SAR11 bacteria were typically as large as, if not larger than, other prokaryotes . Additionally, more than half of SAR11 bacteria assimilated dissolved amino acids and DMSP, whereas about 40% of other prokaryotes assimilated these compounds . Due to their high abundance and activity, SAR11 bacteria were responsible for about 50% of amino acid assimilation and 30% of DMSP assimilation in surface waters . The contribution of SAR11 bacteria to amino acid assimilation was greater than would be expected based on their overall abundance, implying that SAR11 bacteria outcompete other prokaryotes for these labile compounds . These data suggest that SAR11 bacteria are highly active and play a significant role in C, N, and S cycling in the ocean . Aquifex aeolicus PilT, Homologue of a Surface Motility Protein, Is a Thermostable Oligomeric NTPase. Timothy J. Herdendorf, 2002.Bacterial surface motility works by retraction of surface-attached type IV pili . This retraction requires the PilT protein, a member of a large family of putative NTPases from type II and IV secretion systems . In this study, the PilT homologue from the thermophilic eubacterium Aquifex aeolicus was cloned, overexpressed, and purified . A . aeolicus PilT was shown to be a thermostable ATPase with a specific activity of 15.7 nmol of ATP hydrolyzed/min/mg of protein. This activity was abolished when a conserved lysine in the nucleotide-binding motif was altered . The substrate specificity was low; UTP, CTP, ATP, GTP, dATP, and dGTP served as substrates, UTP having the highest activity of these in vitro . Based on sedimentation equilibrium and size exclusion chromatography, PilT was identified as a  5- to 6-subunit oligomer . Potential implications of the NTPase activity of PilT in pilus retraction are discussed .
The Vibrio Pathogenicity Island of Epidemic Vibrio cholerae Forms Precise Extrachromosomal Circular Excision Products. C. Rajanna, 2003.The Vibrio pathogenicity island (VPI) in epidemic Vibrio cholerae is an essential virulence gene cluster . Like many pathogenicity islands, the VPI has at its termini a phage-like integrase gene (int), a transposase-like gene (vpiT), and phage-like attachment (att) sites, and is inserted at a tRNA-like locus (ssrA) . We report that the VPI precisely excises from the chromosome and that its left and right ends join to form an extrachromosomal circular excision product (pVPI) . Two-stage nested PCR analysis and DNA sequencing confirmed the int-att-vpiT junction and that the core attP of pVPI is identical to the chromosomal VPI attR site . Excision was independent of toxR and toxT . Excision was independent of recA, suggesting that it is mediated by site-specific recombination . Interestingly, while excision was detected in int and vpiT mutants, excision was abolished in a double (int vpiT) mutant and was restored by plasmids containing genes for either recombinase . Excision results in deletion of A361 in the ssrA locus, which flanks the right junction of the VPI . Since A361 encodes U70 in the critical G · U base pair in the acceptor stem of the ssrA RNA that is the determinant for aminoacylation with alanine, this deletion might have deleterious effects on ssrA function . Also, vpiT may have undergone interchromosomal translocation or may represent an independent integration event, as it was found downstream of hutA in some isolates . Our results provide new insight into the molecular biology of the VPI, and we propose that the process of excision and circularization is important in the emergence, pathogenesis, and persistence of epidemic V . cholerae . Genetic Diversity and Spoilage Potentials among Pseudomonas spp . Isolated from Fluid Milk Products and Dairy Processing Plants. Belgin Dogan, 2003.Degradation of milk components through various enzymatic activities associated with the contamination of dairy products by Pseudomonas spp . can reduce the shelf life of processed milk . Reliable methods for differentiating among Pseudomonas spp . strains are necessary to identify and eliminate specific sources of bacterial contamination from dairy processing systems . To that end, we assessed the genetic diversity and dairy product spoilage potentials among a total of 338 Pseudomonas spp . isolates from raw and pasteurized milk and from environmental samples collected from four dairy processing plants . The majority of isolates were identified as P . fluorescens and P . putida by API 20 NE . A total of 42 different ribotype patterns were identified among a subset of 81 isolates . The presence of many different ribotypes within this collection indicates high genetic diversity among the isolates and suggests multiple origins of contamination within the processing plant and in dairy products . The extracellular enzyme activity patterns among Pseudomonas isolates appeared to be associated with ribotypes . Isolates with the same ribotype frequently had the same extracellular protease, lecithinase, and lipase activities . For example, isolates grouped in ribotype 55-S-6 had the highest extracellular protease activity, while those in ribotypes 50-S-8 and 72-S-3 had the highest extracellular lipase activities . We conclude that ribotyping provides a reliable method for differentiating Pseudomonas strains with dairy food spoilage potential . Isolation and Characterization of Novel Psychrophilic, Neutrophilic, Fe-Oxidizing, Chemolithoautotrophic  - and
 -Proteobacteria from the Deep Sea.K. J. Edwards, 2003.We report the isolation and physiological characterization of novel, psychrophilic, iron-oxidizing bacteria (FeOB) from low-temperature weathering habitats in the vicinity of the Juan de Fuca deep-sea hydrothermal area . The FeOB were cultured from the surfaces of weathered rock and metalliferous sediments . They are capable of growth on a variety of natural and synthetic solid rock and mineral substrates, such as pyrite (FeS2), basalt glass (  10 wt% FeO), and siderite (FeCO3), as their sole energy source, as well as numerous aqueous Fe substrates . Growth temperature characteristics correspond to the in situ environmental conditions of sample origin; the FeOB grow optimally at 3 to 10°C and at generation times ranging from 57 to 74 h . They are obligate chemolithoautotrophs and grow optimally under microaerobic conditions in the presence of an oxygen gradient or anaerobically in the presence of nitrate . None of the strains are capable of using any organic or alternate inorganic substrates tested . The bacteria are phylogenetically diverse and have no close Fe-oxidizing or autotrophic relatives represented in pure culture . One group of isolates are
-Proteobacteria most closely related to the heterotrophic bacterium Marinobacter aquaeolei (87 to 94% sequence similarity) . A second group of isolates are
-Proteobacteria most closely related to the deep-sea heterotrophic bacterium Hyphomonas jannaschiana (81 to 89% sequence similarity) . This study provides further evidence for the evolutionarily widespread capacity for Fe oxidation among bacteria and suggests that FeOB may play an unrecognized geomicrobiological role in rock weathering in the deep sea .
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