Xenorhabdus and Photorhabdus are gram-negative bacteria that produce a range of proteins that are toxic to insects. We recently identified a novel 42-kDa protein from Xenorhabdus nematophila that was lethal to the larvae of insects such as Galleria mellonella and Helicoverpa armigera when it was injected at doses of 30 to 40 ng/g larvae. In the present work, the toxin gene txp40 was identified in another 59 strains of Xenorhabdus and Photorhabdus, indicating that it is both highly conserved and widespread among these bacteria. Recombinant toxin protein was shown to be active against a variety of insect species by direct injection into the larvae of the lepidopteran species G. mellonella, H. armigera, and Plodia interpunctella and the dipteran species Lucilia cuprina. The protein exhibited significant cytotoxicity against two dipteran cell lines and two lepidopteran cell lines but not against a mammalian cell line. Histological data from H. armigera larvae into which the toxin was injected suggested that the primary site of action of the toxin is the midgut, although some damage to the fat body was also observed.
The growth of minute virus of mice (MVM) in L cells was followed by plaque assay of both cell-associated and free virus at intervals up to 36 h after infection. The major production of progeny virus occurred after incubation for 27 h and most of the virus remained cell-associated. L cells infected with MVM were pulse-labeled with 3H-thymidine for 6 h preceding induction of lysis with sodium dodecylsulfate. Two new species of DNA remained in the supernatant fractions from lysates after selective precipitation by 1 M NaCl of cellular DNA. These first appeared 17 h after infection. On the basis of sedimentation rates and response to heating and to treatment with alkali, one of these species is a hydrogen-bonded duplex molecule, which on denaturation hybridized with the single-stranded DNA of MVM virions.
The facultatively chemoheterotrophic blue-green bacterium Aphanocapsa 6714 accumulates two novel, stable ribonucleic acid species when deprived of sources of carbon and energy. At least one of these species is nonribosomal.We previously described (7) the stable ribonucleic acid (RNA) species produced by unilluminated cultures of the obligately photoautotrophic blue-green bacterium Anacystis nidulans. In addition to known ribosomal RNAs (rRNA's) (5S, 16S, and 23S rRNA) and two in vivo 23S rRNA cleavage products (3), these always include two novel species of unknown origin and function. These last have apparent molecular weights of 0.33 x 106 and 0.16 x 106 and may be related in sequence, since mild (urea) denaturation converts the former into material migrating with the latter on polyacrylamide gels (3). Two additional unusual species (0.24 x 106 and 0.12 x 106 daltons), which appear similarly related, are occasionally seen in such experiments. All four novel RNAs are stable only in darkened cultures; they rapidly disappear when such cultures are reilluminated and can only be identified in continuously illuminated cells as part of the populationIof rapidly turning-over, unstable RNA.In an effort to extend these observations we have now examined stable RNAs of the five unicellular blue-green bacterial strains designated by Stanier 6307, 6312, 6701, 6714, and 7002 (9). In the dark each strain produces one or more stable RNA species that are not present in long-term labeled RNA from illuminated cultures. Of particular interest are results with Aphanocapsa 6714, a facultative chemoheterotroph which, unlike A. nidulans, is capable of dark growth on glucose (6). Figure 1 shows results of electrophoresis of a urea-denatured mixture of RNA from A. nidulans (labeled in darkness with ['4C]uracil) and RNA from Aphanocapsa 6714 (labeled in darkness with [3H]uracil). Of the seven stable Aphanocapsa RNA species resolved, five are also seen in labeled material from illuminated cultures of this organism and can be accounted for as either mature 23S and 16S rRNA (1.1 x 106 and 0.52 x 106 daltons, respectively), precursor to 16S rRNA (0.67 x 106 daltons), or postmaturational cleavage products of 23S rRNA (0.90 x 106 and 0.17 x 106 daltons [3]). The remaining two (0.12 x 106 and 0.09 x 106 daltons) are seen only in nongrowing darkened cells (Fig. 2) or illuminated cells in which CO2 fixation has been blocked by the photosystem II inhibitor DCMU (3-[3,4-dichlorophenyl]-1,1-dimethylurea; data not shown). They are not seen in RNA from darkened cells growing in the presence of glucose or in RNA from illuminated cells growing in the absence of DCMU (Fig. 2). Thus their presence reflects reduction in availability of fixed carbon or energy and is not a direct consequence of darkness. (It should be noted that darkened cultures ofA. nidulans do not produce material comigrating with the most rapidly migrating RNA from Aphanocapsa 6714.)Blue-green bacterial 23S rRNA is characteristically unstable (3) and we suggested earlier (7) that novel RN...
The immunochemical specificity of the observed cross-reactivity between Escherichia coli strain 101 and Staphylococcus aureus strain Mardi was examined. The cross-reactivity was shown to be dependent upon mucopeptide antibodies which are present in normal and immune sera. Although both organisms contained surface antigens with immunodominant glucuronic acid residues, in vitro phagocytosis studies indicated that antibodies directed against these antigens were not significantly involved in the opsonization process. Rather, antibodies with mucopeptide specificity were shown to be involved in the in vitro phagocytosis of these organisms by polymorphonuclear leukocytes. The mucopeptide antibodies, which were found in both nonimmune and immune sera, were shown to be effective in opsonizing both the S. aureus strain and the E. coli strain. The ubiquitous distribution of E. coli strains containing mucopeptide antigens common to most bacteria suggests that these organisms may be responsible for the wide prevalence of natural staphylococcal opsonins with mucopeptide specificity in normal sera.
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