Identification and Characterization of a Shuttle Plasmid with Antibiotic Resistance Gene from <Emphasis Type="Italic">Staphylococcus aureus</Emphasis>

While studying antibiotic-resistant plasmids from multi-drug-resistant nosocomial Staphylococcus aureus strains, we isolated a small (2.889 kb) chloramphenicol-resistant (Cm^r) plasmid, which was designated as pMC524/MBM. The molecular size of pMC524/MBM was close to that of pC194 (2.910 kb), a well-known Cm^r staphylococcal plasmid. Unlike pC194, this plasmid can replicate and express itself efficiently and stably in Escherichia coli. However, Cm is needed for stable maintenance of pMC524/MBM in different hosts. In this study, the nucleotide sequences of these two plasmids were compared after sequencing of pMC524/MBM [EMBL Accession No. AJ312056 SAU312056]. Although these two plasmids have striking nucleotide sequence homology, the Plus Origin, Minus Origin, the replication protein (Rep), and the chloramphenicol acetyl transferase (Cat) have considerable variations. Possibly, these changes have modulated pMC524/MBM into an efficient shuttle-plasmid. Received: 8 April 2002 / Accepted: 27 July 2002     

Role of carcinoscorpin, a haemolymph lectin of horseshoe crabCarcinoscorpius rotundacauda as humoral factor

This study demonstrated that a marine Indian horseshoe crab,Carcinoscorpious rotundacauda showed higher self defence in an experimental infection upon the induction of its circulatory lectin, carcinoscorpin. It resisted an infection with 10⁷ liveEscherichia coli per crab when the circulatory carcinoscorpin was 8–16-fold higher after administering 2-ketodeoxyoctonate (Kdo) into the live crab. The naive control with its natural level of circulatory lectin could tolerate a maximum infective dose of 10⁶ liveE. coli per crab. Bacterial killing and phagocytic uptake in association with the isolated crab amoebocytes in anex vivo system was considerably higher for the lectin opsonizedE. coli compared to unopsonized samples. Carcinoscorpin is thus functionally an opsonin in the defence of the primitive marine arthropod,C. rotundacauda, like vertebrate antibody, a humoral factor involved in the defence of the host. The natural capacity for defending an infection with 10⁶ liveE. coli per crab suggested that the crabs in the natural habitat hardly face such an infection and is possibly one of the reasons for its survival over millions of years as a living fossil.     

Berberine–DNA complexation: New insights into the cooperative binding and energetic aspects

The equilibrium binding of the cytotoxic plant alkaloid berberine to various DNAs and energetics of the interaction have been studied. At low ratios of bound alkaloid to base pair, the binding exhibited cooperativity to natural DNAs having almost equal proportions of AT and GC sequences. In contrast, the binding was non-cooperative to DNAs with predominantly high AT or GC sequences. Among the synthetic DNAs, cooperative binding was observed with poly(dA).poly(dT) and poly(dG).poly(dC) while non-cooperative binding was seen with poly(dA–dT).poly(dA–dT) and poly(dG–dC).poly(dG–dC). Both cooperative and non-cooperative bindings were remarkably dependent on the salt concentration of the media. Linear plots of ln K_a versus [Na⁺] for poly(dA).poly(dT) and poly(dA–dT).poly(dA–dT) showed the release of 0.56 and 0.75 sodium ions respectively per bound alkaloid. Isothermal titration calorimetry results revealed the binding to be exothermic and favoured by both enthalpy and entropy changes in all DNAs except the two AT polymers and AT rich DNA, where the same was predominantly entropy driven. Heat capacity values (ΔCp^o) of berberine binding to poly(dA).poly(dT), poly(dA–dT).poly(dA–dT), Clostridium perfringens and calf thymus DNA were − 98, − 140, − 120 and − 110 cal/mol K respectively. This study presents new insights into the binding dependent base pair heterogeneity in DNA conformation and the first complete thermodynamic profile of berberine binding to DNAs.