Motile aeromonas infection of striped (grey) mullet Mugil cephalus

Infection of striped mullet (Mugil cephalus) with Aeromonas hydrophila results in an acute septicemic disease. The disease can be experimentally induced by intramuscular injection, skin or gill scarification or by the oral route using pellets purposely seeded with bacteria. The organism was isolated from the blood 1–2 days after infection and from all organs 24 hr or longer after infection. The disease is characterized by early inflammatory and proliferative changes and later necrotic changes. Enteritis and hepatic necrosis are constant findings in aeromonad disease of M. cephalus but surface lesions are not pathognomic for these infections in mullet. Death of infected fish may be attributed to bacterial toxins which cause necrosis of parenchymal organs and soft tissue structure.     

Molecular Characterization of a Deep-Sea Methanotrophic Mussel Symbiont that Carries a RuBisCO Gene

In our previous investigation on the genes of 1,5-ribulose bisphosphate carboxylase/oxygenase (RuBisCO; EC 4.1.1.39) in deep-sea chemoautotrophic and methanotrophic endosymbioses, the gene encoding the large subunit of RuBisCO form I (cbbL) had been detected in the gill of a mussel belonging to the genus Bathymodiolus from a western Pacific back-arc hydrothermal vent. This study further examined the symbiont source of the RuBisCO cbbL gene along with the genes of 16S ribosomal RNA (16S rDNA) and particulate methane monooxygenase (EC 1.14.13.25; pmoA) and probed for the presence of the ATP sulfurylase gene (EC 2.7.7.4; sopT). The 16S rDNA sequence analysis indicated that the mussel harbors a monospecific methanotrophic Gammaproteobacterium. This was confirmed by amplification and sequencing of the methanotrophic pmoA, while thiotrophic sopT was not amplified from the same symbiotic genome DNA. Fluorescence in situ hybridization demonstrated simultaneous occurrence of the symbiont-specific 16S rDNA, cbbL and pmoA, but not sopT, in the mussel gill. This is the first molecular and visual evidence for a methanotrophic bacterial endosymbiont that bears the RuBisCO cbbL gene relevant to autotrophic CO₂ fixation.     

Composition of archaeal,bacterial, and eukaryal RuBisCO genotypes in three Western Pacific arc hydrothermal vent systems

We studied the diversity of all forms of the RuBisCO large subunit-encoding gene cbbL in three RuBisCO uncharacterized hydrothermal vent communities. This diversity included the archaeal cbbL and the forms IC and ID, which have not previously been studied in the deep-sea environment, in addition to the forms IA, IB and II. Vent plume sites were Fryer and Pika in the Mariana arc and the Suiyo Seamount, Izu-Bonin, Japan. The cbbL forms were PCR amplified from plume bulk microbial DNA and then cloned and sequenced. Archaeal cbbL was detected in the Mariana samples only. Both forms IA and II were amplified from all samples, while the form IC was amplified only from the Pika and Suiyo samples. Only the Suiyo sample showed amplification of the form ID. The form IB was not recorded in any sample. Based on rarefaction analysis, nucleotide diversity and average pairwise difference, the archaeal cbbL was the most diverse form in Mariana samples, while the bacterial form IA was the most diverse form in the Suiyo sample. Also, the Pika sample harbored the highest diversity of cbbL phylogenetic lineages. Based on pairwise reciprocal library comparisons, the Fryer and Pika archaeal cbbL libraries showed the most significant difference, while Pika and Suiyo showed the highest similarity for forms IA and II libraries. This suggested that the Fryer supported the most divergent sequences. All archaeal cbbL sequences formed unique phylogenetic lineages within the branches of anaerobic thermophilic archaea of the genera Pyrococcus, Archaeoglobus, and Methanococcus. The other cbbL forms formed novel phylogenetic clusters distinct from any recorded previously in other deep-sea habitats. This is the first evidence for the diversity of archaeal cbbL in environmental samples.     

A pseudocystic lipoma in the European eel (Anguilla anguilla)

This is the first report of lipoma in the European eel Anguilla anguilla. In a single eel that was obtained from a polyculture fish farm in northern Egypt, a yellowish swelling (10 mm in diameter) was observed near the tip of the lower lip. The tumor was composed of mature lipocytes that occasionally fused into an unlined cystic space.     

Sequestered actin in chick embryo fibroblasts

Chick embryo fibroblasts contain about 75-100 M unpolymerized actin and at least four proteins which can bind actin monomers, actin depolymerizing factor (ADF), gelsolin, profilin, and thymosin ₄ (T₄). Fibroblast extracts are analyzed by non-denaturing polyacrylamide gel electrophoresis and immunoblotting where most of the G-actin is detected as a complex with T₄. When fibroblast extracts are fractionated by gel filtration and the fractions are analyzed by PAGE and HPLC, most of the G-actin elutes in a peak that also contains T₄ at an overall molar ratio of 1.9:1 relative to actin. Gelsolin, profilin, and ADF are also detectable in the gel filtration eluate and at least partly coelute with actin, and account for only a minor fraction of the soluble actin pool. These observations indicate that under the growth conditions studied, T₄ is the major actin-sequestering protein in fibroblasts.     

Characterization of the skin collagen of a surface water fish Scomberoides commersonianus.

The molecular organization of the skin collagen in the fish S. commersonianus has been investigated. The contents of imino acids proline and hydroxyproline are less in the skin collagen. The major collagenous component of fish skin is homologous to type I collagen. The number of CNBr peptides in fish skin collagen alpha 1 chains is two times that of rat skin alpha 1 CNBr peptides. The proline-hydroxyproline ratio in the six peptides studied was 1.66-3.5 as compared to that of rat skin collagen (0.67-1.94). This indicates that proline and hydroxyproline are not uniformly distributed in the collagen molecule in fish skin collagen.     

Increasing cleavage specificity and activity of restriction endonuclease KpnI

Restriction enzyme KpnI is a HNH superfamily endonuclease requiring divalent metal ions for DNA cleavage but not for binding. The active site of KpnI can accommodate metal ions of different atomic radii for DNA cleavage. Although Mg²⁺ ion higher than 500 μM mediates promiscuous activity, Ca²⁺ suppresses the promiscuity and induces high cleavage fidelity. Here, we report that a conservative mutation of the metal-coordinating residue D148 to Glu results in the elimination of the Ca²⁺-mediated cleavage but imparting high cleavage fidelity with Mg²⁺. High cleavage fidelity of the mutant D148E is achieved through better discrimination of the target site at the binding and cleavage steps. Biochemical experiments and molecular dynamics simulations suggest that the mutation inhibits Ca²⁺-mediated cleavage activity by altering the geometry of the Ca²⁺-bound HNH active site. Although the D148E mutant reduces the specific activity of the enzyme, we identified a suppressor mutation that increases the turnover rate to restore the specific activity of the high fidelity mutant to the wild-type level. Our results show that active site plasticity in coordinating different metal ions is related to KpnI promiscuous activity, and tinkering the metal ion coordination is a plausible way to reduce promiscuous activity of metalloenzymes.     

Nucleolar protein B23/nucleophosmin regulates the vertebrate SUMO pathway through SENP3 and SENP5 proteases

Ubiquitin-like protein/sentrin-specific proteases (Ulp/SENPs) mediate both processing and deconjugation of small ubiquitin-like modifier proteins (SUMOs). Here, we show that Ulp/SENP family members SENP3 and SENP5 localize within the granular component of the nucleolus, a subnucleolar compartment that contains B23/nucleophosmin. B23/nucleophosmin is an abundant shuttling phosphoprotein, which plays important roles in ribosome biogenesis and which has been strongly implicated in hematopoietic malignancies. Moreover, we found that B23/nucleophosmin binds SENP3 and SENP5 in Xenopus laevis egg extracts and that it is essential for stable accumulation of SENP3 and SENP5 in mammalian tissue culture cells. After either codepletion of SENP3 and SENP5 or depletion of B23/nucleophosmin, we observed accumulation of SUMO proteins within nucleoli. Finally, depletion of these Ulp/SENPs causes defects in ribosome biogenesis reminiscent of phenotypes observed in the absence of B23/nucleophosmin. Together, these results suggest that regulation of SUMO deconjugation may be a major facet of B23/nucleophosmin function in vivo.     

SUSP1 antagonizes formation of highly SUMO2/3-conjugated species

Small ubiquitin-related modifier (SUMO) processing and deconjugation are mediated by sentrin-specific proteases/ubiquitin-like proteases (SENP/Ulps). We show that SUMO-specific protease 1 (SUSP1), a mammalian SENP/Ulp, localizes within the nucleoplasm. SUSP1 depletion within cell lines expressing enhanced green fluorescent protein (EGFP) fusions to individual SUMO paralogues caused redistribution of EGFP-SUMO2 and -SUMO3, particularly into promyelocytic leukemia (PML) bodies. Further analysis suggested that this change resulted primarily from a deficit of SUMO2/3-deconjugation activity. Under these circumstances, PML bodies became enlarged and increased in number. We did not observe a comparable redistribution of EGFP-SUMO1. We have investigated the specificity of SUSP1 using vinyl sulfone inhibitors and model substrates. We found that SUSP1 has a strong paralogue bias toward SUMO2/3 and that it acts preferentially on substrates containing three or more SUMO2/3 moieties. Together, our findings argue that SUSP1 may play a specialized role in dismantling highly conjugated SUMO2 and -3 species that is critical for PML body maintenance.