Purification and properties of a manganese-stimulated endonuclease from Bacillus subtilis

Purification and characterization of a Bacillus subtilis 168 nuclease, YokF, involved in chromosomal DNA degradation and cell death caused by thermal shock treatments

We purified and characterized a 39-kDa Bacillus subtilis 168 nuclease that has been suggested in this laboratory to be involved in chromosomal DNA degradation induced by lethal heat and cold shock treatments in vivo. The nuclease activity was inhibited in vitro by aurintricalboxylic acid but not by Zn(2+). By the mutant analysis, we identified the 39-kDa nuclease as a product of yokF gene. The yokF gene contained a putative lipoprotein signal peptide motif. After in vivo exposure to lethal heat and cold stresses, the chromosomal DNA fragmentation was reduced in the yokF mutant, which demonstrated about a 2-10-fold higher survival rate than the wild type. The yokF mutant was found to be more sensitive to mitomycin C than the wild type. The transformation efficiency of the yokF mutant was about 10 times higher than that of the wild type. It is suggested that when B. subtilis cells are exposed to a stressful thermal shock resulting in membrane perturbation, YokF nuclease consequently dislocates into the cytoplasm and then attacks DNA.

Manganese: its acquisition by and function in the lactic acid bacteria

The transition metal manganese is considered to be a minor micronutrient in both pro- and eukaryotes, usually being required from the environment at subnanomolar levels. Until recently, Mn was only known to function in cells as a cofactor for a few enzymatic reactions. A notable exception has been reported in many lactic acid bacterial species which require micromolar medium Mn levels for growth and contain up to 35 mM Mn. These high Mn concentrations are accompanied by the near or complete absence of intracellular iron and superoxide dismutase (SOD). Lacking hemes, Lactobacillus plantarum and related species contain a unique Mn-cofactored catalase as well as millimolar Mn(II) in a nonenzymic complex performing the function of the micromolar superoxide dismutase found in most other aerotolerant cells. The high Mn(II) levels are accumulated via an efficient active transport system and are stored intracellularly in a high molecular weight complex. Study of Lactobacillus plantarum has provided an interesting example of the substitution of Mn for Fe in several of the biological roles of Fe, an alternative mechanism of aerotolerance, and a better understanding of the unique biochemistry of the lactic acid bacteria.

Intracellular nuclease activities of buffalo rumen bacterial population

Nuclease activities of the predominantly bacterial population obtained from buffalo rumen were investigated. Optimum temperature for hydrolysis of both DNA and RNA was 50 degrees C whereas DNAase activity was observed to be stable up to 50 degrees C, a decrease in RNAase activity was observed even after 40 degrees C. Two pH optima, one at 5.5 and the other at 7.5, were recorded for hydrolysis of DNA. RNAase activity was maximum between pH 6.0 to 7.0. Whereas DNAase activity was stable near its optimum pH, RNAase activity was stable between pH 7.0 to 8.5. Mn2+ ions stimulated DNAase activity. It was strongly inhibited by Hg2+, Zn2+, Pb2+ and Ag+. RNAase activity was stimulated by Mg2+ ions and was strongly inhibited by Hg2+, Cu2+, Zn2+ and Ag+. Cysteine hydrochloride and 2-mercaptoethanol stimulated DNAase activity. The activity was strongly inhibited by N-ethylmaleimide, 4-chloromercuribenzoate, 8-quinolinol, iodoacetic acid and 1,10-phenanthroline. RNAase activity was stimulated by cysteine hydrochloride, reduced glutathione and 2-mercaptoethanol and was strongly inhibited by 4-chloromercuribenzoate, 8-quinolinol and 2,2'bipyridyl.

Molecular cloning with bifunctional plasmid vectors in Bacillus subtilis. II. Transfer of sequences propagated in Escherichia coli to B. subtilis

Recombinant plasmid DNA cloned in E. coli via the bifunctional vector pDH5060 suffered deletions when returned to B. subtilis. However, DNA preparations of identical chimeras containing homologous or heterologous sequences stably transformed B. subtilis at high efficiency when isolated from B. subtilis. The vector pDH5060, however, was not affected and could be stably shuttled between E. coli and B. subtilis at high frequency. These problems affected the transfer of clone pools and individual chimeras, irrespective of the restriction or recombination phenotype of B. subtilis recipients. Deleted chimeras lost at least one end of cloned inserts, and in most cases, flanking plasmid sequences. Single plasmid forms (intact or deleted) were isolated from several hundred individual Cmr-transformants this suggests that events leading to deletion of chimeric plasmid DNA occur during transformation by restriction of unmodified insert sequences propagated in the intermediate host, E. coli. This conclusion is discussed with regard to the mechanism of plasmid transformation in B. subtilis.

Transformation-deficient mutants of Bacillus subtilis impaired in competence-specific nuclease activities

A comparison of the nucleolytic activities in competent and physiologically low-competent wild-type cultures of Bacillus subtilis in DNA-containing sodium dodecyl sulfate-polyacrylamide gels revealed the existence of three competence-associated nuclease activities with apparent molecular weights of 13,000, 15,000, and 26,000. The three activities, which were dependent on manganese or magnesium ions, were specifically present in the competent fraction of a competent culture. The competence-associated nucleolytic activities of eight transformation-defective mutant strains were assayed, resulting in the following three classes of mutants: (i) four strains which, according to this assay, were not impaired in any of the nucleolytic activities mentioned above; (ii) one strain which was strongly impaired in the 13,000- and 26,000-molecular-weight activities, but showed a considerable level of the 15,000-molecular-weight activity; and (iii) three strains which were severely impaired in all three activities. The results indicated that the 26,000-molecular-weight activity was a dimer of the 13,000-molecular-weight activity and that this nuclease was involved in the entry of DNA.

Transformation in Bacillus subtilis with nitrogen mustard crosslinked DNA. Effect on cotransformation and mutation frequencies

Bacillus subtilis DNA was treated in vitro with nitrogen mustard and the crosslinked molecules were purified, after alkali denaturation, by hydroxyapatite chromatography. When tested for the ability to transform the trpC2-hisB2 segment, these molecules exhibited a decrease in the cotransformation index (r) as compared to native or renatured DNA. The decrease in r was not accompanied by an increase in mutagenicity.

Purification and properties of a manganese-stimulated deoxyribonuclease produced during sporulation of Bacillus subtilis

A DNAase (deoxyribonuclease) was isolated from culture supernatants of sporulating Bacillus subtilis 168. The purified enzyme migrated as a single band during polyacrylamide-gel electrophoresis. The enzyme differs from other DNAases of B. subtilis in molecular weight, metal-ion requirement and mode of action. The enzyme was inactive in the absence of metal ions, and exhibited optimum activity with 10 mM-Mn2+, although Mg2+, Cd2+ and Co2+ could also permit some activity. The pH optimum for the enzyme was pH 7.5, and it degraded linear-duplex DNA or closed-circular-duplex DNA to acid-soluble material. There was little or no activity on single-stranded DNA or rRNA. Sucrose-gradient analysis of the products of DNAase action on bacteriophage T7 DNA showed that endonucleolytic cleavage had occurred by the introduction of single-strand breaks in both strands of the duplex. The molecular weight of the enzyme was determined, by gel filtration on Sephadex G-75, to be 12000.

Properties of the high-molecular-weight deoxyribonuclease of Bacillus subtilis degrading single-stranded DNA

We have studied the properties of the high-Mr DNAse degrading single-stranded DNA which is present in extracts of Bacillus subtilis. This enzyme is a heterogeneous aggregate of identical subunits with an Mr of 36 000, as measured in dodecylsulfate/polyacrylamide electrophoresis. The aggregate can be disassembled by the presence of Triton X-100, but reforms spontaneously following removal of the detergent. A mild proteolytic treatment of the aggregate causes the irreversible and nearly quantitative conversion into the free subunit. The modified subunit has identical properties (in terms of size, chromatographic adsorption and catalytic activity) as the small DNAse previously described by Ciarrocchi et al. [Eur. J. Biochem. 61, 487 (1976)], i.e. an endonuclease highly specific for single-stranded DNA and producing 5'-P and 3'-OH ends.