Role of DNase in recovery of plasmid DNA from Clostridium perfringens

Clostridium autoethanogenum isopropanol production via native plasmid pCA replicon

Clostridium autoethanogenum is a model gas-fermenting acetogen for commercial ethanol production. It is also a platform organism being developed for the carbon-negative production of acetone and isopropanol by gas fermentation. We have assembled a 5.5 kb pCA plasmid for type strain DSM10061 (JA1-1) using three genome sequence datasets. pCA is predicted to encode seven open-reading frames and estimated to be a low-copy number plasmid present at approximately 12 copies per chromosome. RNA-seq analyses indicate that pCA genes are transcribed at low levels and two proteins, CAETHG_05090 (putative replication protein) and CAETHG_05115 (hypothetical, a possible Mob protein), were detected at low levels during batch gas fermentations. Thiolase (thlA), CoA-transferase (ctfAB), and acetoacetate decarboxylase (adc) genes were introduced into a vector for isopropanol production in C. autoethanogenum using the native plasmid origin of replication. The availability of the pCA sequence will facilitate studies into its physiological role and could form the basis for genetic tool optimization.

A Molecular Biology Tool Kit for the Phototrophic Firmicute Heliobacterium modesticaldum

The heliobacteria are members of the bacterial order Clostridiales and form the only group of phototrophs in the phylum Firmicutes Several physiological and metabolic characteristics make them an interesting subject of investigation, including their minimalist photosynthetic system, nitrogen fixation abilities, and ability to reduce toxic metals. While the species Heliobacterium modesticaldum is an excellent candidate as a model system for the family Heliobacteriaceae, since an annotated genome and transcriptomes are available, studies in this organism have been hampered by the lack of genetic tools. We adapted techniques for genetic manipulation of related clostridial species for use with H. modesticaldum Five heliobacterial DNA methyltransferase genes were expressed in an Escherichia coli strain engineered as a conjugative plasmid donor for broad-host-range plasmids. Premethylation of the shuttle vectors before conjugation into H. modesticaldum is absolutely required for production of transconjugant colonies. The introduced shuttle vectors are maintained stably and can be recovered using a modified minipreparation procedure developed to inhibit endogenous DNase activity. Furthermore, we describe the formulation of various growth media, including a defined medium for metabolic studies and isolation of auxotrophic mutants.IMPORTANCE Heliobacteria are anoxygenic phototrophic bacteria with the simplest known photosynthetic apparatus. They are unique in using bacteriochlorophyll g as their main pigment and lacking a peripheral antenna system. Until now, research on this organism has been hampered by the lack of a genetic transformation system. Without such a system, gene knockouts, site-directed mutations, and gene expression studies cannot be performed to help us further understand or manipulate the organism. Here we report the genetic transformation of a heliobacterium, which should enable future genetic studies in this unique phototrophic organism.

Isolation of thermophilic acetogens and transformation of them with the pyrF and kan(r) genes

The application of microbial catalysts to syngas from the gasification of lignocellulosic biomass is gaining interest. Acetogens, a group of anaerobic bacteria, can grow autotrophically on gaseous substrates such as hydrogen and carbon dioxide or syngas and produce acetate via the acetyl-CoA pathway. Here, we report the isolation from a soil sample of two thermophilic acetogen strains, Y72 and Y73, that are closely related to Moorella sp. HUC22-1 and M. thermoacetica ATCC39073. The optimal growth temperature and pH for the strains were 60 °C and 6.0-6.5. Uracil auxotrophy was induced in them by replacing the orotate monophosphate decarboxylase gene (pyrF) with the kanamycin resistant marker (kan(r)). The transformants were isolated by supplementation of the basal medium with 300 mg/L of kanamycin. The transformation efficiency of strains Y72 and Y73 was 20-fold higher than that of strain ATCC39073. Hence these strains are considered possible hosts for thermophilic syngas fermentation.

Phenylobacterium muchangponense sp. nov., isolated from beach soil, and emended description of the genus Phenylobacterium

A Gram-staining-negative, non-motile, aerobic bacterium, designated strain A8T, was isolated from the beach soil of Muchangpo, Korea. Cells were rod-shaped (0.5-0.6×0.7-1.3 µm) and colonies were colourless, circular with entire edges and had a glistening surface. The isolate grew optimally at 25-35 °C and did not require NaCl for growth. Strain A8T could not assimilate acetate, DL-lactate, succinate, antipyrine or chloridazon, but weakly assimilated L-phenylalanine. Major fatty acids were summed feature 7 (comprising C18:1ω7c/ω9t/ω12t), C16:0 and summed feature 4 (comprising C16:1ω7c/ iso-C15:0 2-OH). The major isoprenoid quinone was ubiquinone-10 and the DNA G+C content was 72.3 mol%. Comparative 16S rRNA gene sequence studies showed that strain A8T belonged to the family Caulobacteraceae, class Alphaproteobacteria and was most closely related to type strains of members of the genus Phenylobacterium (95.7-97.1 % similarity). Signature nucleotides and phylogenetic analysis of the 16S rRNA gene sequence also suggested that strain A8T was affiliated with the genus Phenylobacterium. Low DNA-DNA relatedness values (3.0±1.8-11.5±3.2 %) indicated that strain A8T represented a distinct species that was separated from other type strains in the genus Phenylobacterium. On the basis of evidence from a polyphasic study, it is proposed that strain A8T (=KACC 15042T=LMG 25973T) represents the type strain of a novel species, Phenylobacterium muchangponense sp. nov. An emended description of the genus Phenylobacterium is also presented.

Molecular subtyping of poultry-associated type A Clostridium perfringens isolates by repetitive-element PCR

Clostridium perfringens strains (type A) isolated from an integrated poultry operation were subtyped using repetitive-element PCR with Dt primers. Isolates were obtained from fecal, egg shell, fluff, and carcass rinse samples as part of a previously reported temporally linked epidemiological survey. A total of 48 isolates of C. perfringens were obtained from different stages of the broiler chicken production chain from two separate breeder farms that supplied a single hatchery that in turn provided chicks to a single grow-out farm whose flocks were processed at a single plant. All 48 isolates were typeable (100% typeability) by repetitive-element PCR with Dt primers. This subtyping method was highly reproducible and discriminatory. By repetitive-element PCR with Dt primers, isolates were classified into four major branches with 12 subgroups or clades. The Simpson's index of discrimination was calculated to be 0.96 for groupings of >95% correlation. Toxin gene profiles of the isolates indicated that all of the isolates were C. perfringens alpha-toxin gene positive and 46 of 48 isolates were beta2-toxin gene positive. All strains were negative for beta- and epsilon-toxin genes. Repetitive sequence-based PCR was found to be a technically practical and reproducible means of subtyping C. perfringens libraries from specific epidemiological or production environment settings.

Involvement of an extracellular protease in algicidal activity of the marine bacterium Pseudoalteromonas sp. strain A28

The marine bacterium Pseudoalteromonas sp. strain A28 was able to kill the diatom Skeletonema costatum strain NIES-324. The culture supernatant of strain A28 showed potent algicidal activity when it was applied to a paper disk placed on a lawn of S. costatum NIES-324. The condensed supernatant, which was prepared by subjecting the A28 culture supernatant to ultrafiltration with a 10,000-M(w)-cutoff membrane, showed algicidal activity, suggesting that strain A28 produced extracellular substances capable of killing S. costatum cells. The condensed supernatant was then found to have protease and DNase activities. Two Pseudoalteromonas mutants lacking algicidal activity, designated NH1 and NH2, were selected after N-methyl-N'-nitrosoguanidine mutagenesis. The culture supernatants of NH1 and NH2 showed less than 15% of the protease activity detected with the parental strain, A28. The protease was purified to homogeneity from A28 culture supernatants by using ion-exchange chromatography followed by preparative gel electrophoresis. Paper-disk assays revealed that the purified protease had potent algicidal activity. The purified protease had a molecular mass for 50 kDa, and the N-terminal amino acid sequence was determined to be Ala-Thr-Pro-Asn-Asp-Pro. The optimum pH and temperature of the protease were found to be 8.8 and 30 degrees C, respectively, by using succinyl-Ala-Ala-Pro-Phe-p-nitroanilide as a substrate. The protease activity was strongly inhibited by phenylmethylsulfonyl fluoride, diisopropyl fluorophosphate, antipain, chymostatin, and leupeptin. No significant inhibition was detected with EDTA, EGTA, phenanthroline or tetraethylenepentamine. These results suggest that Pseudoalteromonas sp. strain A28 produced an extracellular serine protease which was responsible for the algicidal activity of this marine bacterium.

Characterisation of Clostridium botulinum groups I and II by randomly amplified polymorphic DNA analysis and repetitive element sequence-based PCR

Random amplified polymorphic DNA analysis (RAPD) and repetitive element sequence-based PCR (rep-PCR) were evaluated with respect to their applicability to characterise Clostridium botulinum group I and II strains, the species causing human botulism. Fifteen group I and 21 group II strains of various geographical and temporal origins were characterised with four single arbitrary RAPD primers at low stringency amplification conditions and with a degenerate REP primer pair at moderately stringent conditions. Ready-To-Go RAPD Analysis Beads and Ready-To-Go PCR Beads were used for PCR reactions with RAPD and rep-PCR, respectively. Arbitrary primer OPJ 6 yielded the most discriminating patterns, and distinguished group II C. botulinum serotypes at the strain level. Group I strains were mainly discriminated at the serotype level. The discriminatory power of rep-PCR was found to be inferior to that of RAPD. The REP1R-Dt and REP2R-Dt primer pair generated group I- and II-specific fragments and arbitrary primer OPJ 13 produced a serotype E-specific fragment. The use of pre-dispensed and pre-optimised beads attributed to highly reproducible results. As compared to more time-consuming typing methods, such as pulsed-field gel electrophoresis (PFGE), both RAPD and rep-PCR were characterised by rapid performance and a typeability of 100%.

Biodiversity of Clostridium botulinum type E strains isolated from fish and fishery products

The genetic biodiversity of Clostridium botulinum type E strains was studied by pulsed-field gel electrophoresis (PFGE) with two macrorestriction enzymes (SmaI-XmaI and XhoI) and by randomly amplified polymorphic DNA (RAPD) analysis with two primers (OPJ 6 and OPJ 13) to characterize 67 Finnish isolates from fresh fish and fishery products, 15 German isolates from farmed fish, and 10 isolates of North American or North Atlantic origin derived mainly from different types of seafood. The effects of fish species, processing, and geographical origin on the epidemiology of the isolates were evaluated. Cluster analysis based on macrorestriction profiles was performed to study the genetic relationships of the isolates. PFGE and RAPD analyses were combined and resulted in the identification of 62 different subtypes among the 92 type E isolates analyzed. High genetic biodiversity among the isolates was observed regardless of their source. Finnish and North American or North Atlantic isolates did not form distinctly discernible clusters, in contrast with the genetically homogeneous group of German isolates. On the other hand, indistinguishable or closely related genetic profiles among epidemiologically unrelated samples were detected. It was concluded that the high genetic variation was probably a result of a lack of strong selection factors that would influence the evolution of type E. The wide genetic biodiversity observed among type E isolates indicates the value of DNA-based typing methods as a tool in contamination studies in the food industry and in investigations of botulism outbreaks.

Genomic analysis of Clostridium botulinum group II by pulsed-field gel electrophoresis

Pulsed-field gel electrophoresis (PFGE) was optimized for genomic analyses of Clostridium botulinum (non-proteolytic) group II. DNA degradation problems caused by extracellular DNases were overcome by fixation of cells with formaldehyde prior to isolation. A rapid (4-h) in situ DNA isolation method was also assessed and gave indistinguishable results. Genomic DNA from 21 strains of various geographical and temporal origins was digested with 15 rare-cutting restriction enzymes. Of these, ApaI, MluI, NruI, SmaI, and XhoI gave the most revealing PFGE patterns, enabling strain differentiation. Twenty strains yielded PFGE patterns containing 13 pulsotypes. From summation of MluI, SmaI, and XhoI restriction fragments, the genome size of C. botulinum group II was estimated to be 3.6 to 4.1 Mb (mean +/- standard deviation = 3,890 +/- 170 kb). The results substantiate that after problems due to DNases are overcome, PFGE analysis will be a reproducible and highly discriminating epidemiological method for studying C. botulinum group II at the molecular level.

Application of typing by pulsed-field gel electrophoresis to the study of Clostridium difficile in a neonatal intensive care unit

Pulsed-field gel electrophoresis (PFGE) analysis of restriction pattern polymorphism was applied to type Clostridium difficile isolated from neonates hospitalized in a neonatal intensive care unit, and the results were compared with those of immunoblot analysis. C. difficile was isolated from fecal specimens of 41 (61%) of 67 neonates during a 5-month investigation. All of these neonates were asymptomatic. Fifty-five C. difficile isolates from 32 patients were analyzed by PFGE after digestion with SmaI and SacII endonucleases and by immunoblotting with 10 different antisera. Fifty-three of 55 isolates from 30 patients were identical by PFGE analysis after SmaI and SacII digestion and immunoblot analysis. Two isolates were different from each other and from the epidemic group by both PFGE and immunoblot analysis. All 53 epidemic isolates were nontoxigenic, while the two remaining isolates were toxigenic. These results suggest that nosocomial spread of nontoxigenic C. difficile infection in the neonatal intensive care unit and suggest that both PFGE and immunoblot are powerful typing tools for the epidemiological study of C. difficile.

Development of a rapid and efficient restriction endonuclease analysis typing system for Clostridium difficile and correlation with other typing systems

A HindIII restriction endonuclease analysis (REA) typing system for total genomic Clostridium difficile DNA including a rapid and efficient method of DNA extraction and a scheme for organizing unique electrophoretic DNA band patterns was developed. REA typing was performed by two extraction methods for 1,965 C. difficile isolates obtained from patients with symptomatic C. difficile disease, asymptomatic patients who were C. difficile culture positive, and environmental surfaces. This isolate collection yielded 206 unique REA types, which were organized into 75 groups. A reference strain representing each unique REA type was chosen for DNA band pattern comparisons, cytotoxin testing, and plasmid analysis. The DNA band patterns utilizing a guanidine thiocyanate-EDTA-Sarkosyl DNA extraction method were 94% reproducible, while the original and sporadically problematic diethyl pyrocarbonate-sodium dodecyl sulfate DNA extraction method was 98% reproducible when readable patterns were obtained. Reference strains from 43 of the 75 groups were cytotoxin positive, 28 groups were cytotoxin negative, and 4 groups included both toxigenic and nontoxigenic strains. Cytotoxicity of isolates with a particular REA type was always consistent with the toxicity of the reference strain for that type. REA typing was able to discriminate strain differences within types identified by the immunoblot (89 isolates), bacteriophage-bacteriocin (44 isolates), and ribotyping (23 isolates) methods. REA typing is a sensitive, discriminating, reproducible, and rapid method for differentiating C. difficile strains and is suitable for large-scale epidemiologic studies.

Cloning and expression in Escherichia coli of the gene encoding an extracellular deoxyribonuclease (DNase) from Aeromonas hydrophila

The gene encoding an extracellular DNase from Aeromonas hydrophila CHC-1 has been cloned and sequenced. Following expression of the dns in Escherichia coli, it was revealed that some of the cloned enzyme was present in the cell-free extracellular supernatant fluid, and there was no cell lysis and concurrent release of cytoplasmic or periplasmic proteins. Therefore, results suggest that E. coli cells were capable of secreting the DNase extracellularly, albeit very inefficiently. The dns is transcribed from its own promoter in E. coli, and expressed as a 25-kDa product, as determined by sodium dodecyl sulfate-polyacrylamide-gel electrophoresis of the culture supernatant preparations followed by a DNA-hydrolysis assay. Nucleotide sequence analysis predicted a single open reading frame of 690 bp encoding a 230-amino acid (aa) polypeptide, with a potential 20-aa signal peptide located at the N terminus of the predicted protein. The deduced aa sequence of the entire protein is highly homologous with that of the DNase of Vibrio cholerae.

Molecular genetics and pathogenesis of Clostridium perfringens

Clostridium perfringens is the causative agent of a number of human diseases, such as gas gangrene and food poisoning, and many diseases of animals. Recently significant advances have been made in the development of C. perfringens genetics. Studies on bacteriocin plasmids and conjugative R plasmids have led to the cloning and analysis of many C. perfringens genes and the construction of shuttle plasmids. The relationship of antibiotic resistance genes to similar genes from other bacteria has been elucidated. A detailed physical map of the C. perfringens chromosome has been prepared, and numerous genes have been located on that map. Reproducible transformation methods for the introduction of plasmids into C. perfringens have been developed, and several genes coding for the production of extracellular toxins and enzymes have been cloned. Now that it is possible to freely move genetic information back and forth between C. perfringens and Escherichia coli, it will be possible to apply modern molecular methods to studies on the pathogenesis of C. perfringens infections.

Factors involved in the electroporation-induced transformation of Clostridium perfringens

The following factors were found to improve the efficiency of transformation of Clostridium perfringens 3624A Rifr Strr: (1) a reduction in cuvette sample volume (DNA and cell suspension) to 0.8 ml, (2) use of a 1 microgram/ml concentration of transforming DNA, (3) use of late-logarithmic phase cells, (4) 3-fold concentration of cell density (3.0 x 10(8) CFU/ml), and (5) a reduction in the pH of the expression and selective plating medium to 6.4. Application of the improved conditions resulted in transformation efficiencies for C. perfringens 3624A Rifr Strr ranging from 7.1 transformants/microgram DNA for plasmic pIP401 to 9.2 x 10(4) transformants per microgram DNA for plasmid pAK201. The greatest transformation efficiency obtained using pAK201 was 9.8 x 10(6) transformants/micrograms DNA for C. perfringens strain 13. Using the improved protocol, pAM beta 1 was transformed at a 42-fold greater level when compared with the values reported earlier [1]. In addition to C. perfringens 3624A Rifr Strr, strains 13, 10543A, 3628C, NTG-4, and 3624A were successfully transformed. Nuclease does not appear to be a factor in the C. perfringens strain-specific electro-transformation protocol.

Recent advances in the genetics of the clostridia

Several laboratories around the world have started work on genetic analysis of clostridia. Interest in this diverse group of anaerobic organisms has grown with increasing awareness of the benefits that may accrue from their biotechnological exploitation. Research to date has focussed on construction of shuttle vectors containing replicons from clostridial and streptococcal plasmids, development of methods for transferring genes, and molecular cloning of genes--especially those involved in toxigenicity, fermentative metabolism and polysaccharide utilization. In selected species gene transfer by protoplast transformation, electroporation and conjugation has been accomplished and transposable elements have been introduced. It can be anticipated that our understanding of the molecular biology of these interesting organisms will grow rapidly in the future, bringing with it improved prospects for rational biotechnological exploitation.

Construction of an Escherichia coli-Clostridium perfringens shuttle vector and plasmid transformation of Clostridium perfringens

A stable shuttle vector which replicates in Escherichia coli and Clostridium perfringens was constructed by ligating a 3.6-kilobase (kb) fragment of plasmid pBR322 with C. perfringens plasmid pHB101 (3.1 kb). The marker for this shuttle plasmid originated from the 1.3-kb chloramphenicol resistance gene of plasmid pHR106. The resulting shuttle vector, designated pAK201, is 8 kb in size and codes for resistance to 20 micrograms of chloramphenicol per ml in both E. coli and C. perfringens. Following shuttle vector construction in E. coli, plasmid pAK201 was transformed into E. coli HB101 and C. perfringens ATCC 3624A, using intact cell electroporation. The transformation frequencies were 10(6) and 10(4) transformants per microgram of DNA in E. coli and C. perfringens, respectively. Restriction enzyme analysis of the chimera isolated from transformants of both microorganisms suggested that the plasmids were identical. Reciprocal transformation experiments in E. coli and C. perfringens indicated no difference in transformation frequency. Plasmid pAK201 was stable in C. perfringens following repeated transfer in the absence of chloramphenicol pressure. The restriction map of plasmid pAK201 shows six unique cut sites which should be useful for future genetic analysis and C. perfringens gene library construction.

Electroporation-induced transformation of intact cells of Clostridium perfringens

Electroporation-induced transformation of intact cells of Clostridium perfringens 3624A with plasmids pAMB1 and pHR106 resulted in 3.8 X 10(-5) and 4.2 X 10(-4) transformants per viable cell, respectively. With respect to shuttle plasmid pHR106, these values represent a greater than 100-fold increase in transformation frequency when compared with the values reported with polyethylene glycol-induced L-phase variants.

Frequency and Characteristics of Plasmids in Bacteria Isolated from Deep-Sea Amphipods

Bacterial strains isolated from deep-sea amphipods were identified, classified, and screened for plasmid content. Plasmids were common, with 11 of 16 isolates carrying one or more plasmids; these ranged in size from 2.9 to 63 megadaltons. Several of the strains demonstrated distinctly different phenotypic traits yet contained plasmids of the same molecular weight. Results of agarose gel electrophoresis, DNA hybridization, and restriction analysis indicate that the plasmids detected in these deep-sea isolates are identical, suggesting that transmission may occur in the deep-sea environment and that plasmids are common in some deep-sea habitats.

Restriction endonuclease analysis of nosocomial isolates of Clostridium difficile

A total of 110 clinical isolates of Clostridium difficile were analyzed by agarose gel electrophoresis by using both bacterial restriction endonuclease analysis (REA) and plasmid profiles. A total of 72 isolates were divided into 12 groups according to their REA patterns. Some 38 isolates exhibited unique patterns. Pattern A occurred in 20% of isolates. Isolates with patterns B, E, and G were cytotoxin negative. The remaining groups were cytotoxin positive. Multiple isolates obtained from two stool specimens were studied to examine the variation in REA profiles found in single specimens. In these specimens no variation in REA profiles was found. The stability of C. difficile was studied by examining sequential in vitro subcultures of a single isolate and strains isolated over a 4-month period from two long-term carriers. REA patterns were stable over time, both in vitro and in vivo. Because plasmid DNA was observed in 53% of isolates, plasmid profiles alone could not be used to study the spread of C. difficile; however, they were necessary for the interpretation of REA patterns in some instances.

Screening for plasmids in the genus Clostridium

A plasmid screening was performed on 150 strains out of 75 clostridial species using a modification of the alkaline-lysis procedure. In 26 strains representing 21 species one or more plasmid bands were detected ranging in size from 3 to more than 100 kilobase pairs. Clostridium aceticum proved to contain a single small plasmid (pCA1) of 5.4 kbp as revealed by restriction analysis and electron microscopy. A physical map of pCA1 has been constructed. Spontaneous mutants of C. aceticum defective in autotrophic growth have been isolated. No direct correlation between plasmid content and autotrophy could be found.

Modified plasmid isolation method for Clostridium perfringens and Clostridium absonum

A rapid plasmid isolation procedure for Clostridium perfringens and C. absonum is described. The ratio of culture volume to lysis buffer volume was found to be crucial for efficient plasmid isolation. The method can be scaled up, without difficulty, for large-scale plasmid preparation.

Rapid extraction of plasmids from Clostridium perfringens

Two rapid methods were evaluated for their extraction of plasmids from Clostridium perfringens. The first method involved lysis of 1 to 2 ml of C. perfringens culture by treatment with hyaluronidase, lysozyme, and sarcosyl. DNA, extracted with phenol-chloroform, was treated with RNase, boiled, and electrophoresed in a 1.2% agarose gel. The second method involved lysis of 2 ml of culture by lysozyme treatment and extraction with alkaline sodium dodecyl sulfate (SDS). Extracted DNA was treated with RNase, boiled, and electrophoresed in a 0.7% agarose gel. Of 57 strains of C. perfringens analyzed by both extraction procedures, 11 were shown to have plasmids by the alkaline SDS method which were missed by the phenol-chloroform extraction method. These new plasmids were of higher molecular mass and ranged up to 68 megadaltons. Use of the DNase inhibitor diethyl pyrocarbonate did not further improve the yield of plasmid DNA. An additional 159 isolates of C. perfringens screened by the alkaline SDS method revealed plasmids up to 80 megadaltons in mass and an overall plasmid carriage rate of 69%.

Production of toxin by Clostridium botulinum type A strains cured by plasmids

Twelve strains of Clostridium botulinum type A and seven strains of Clostridium sporogenes were screened for plasmids by agarose gel electrophoresis of cleared lysates of cells from 5 ml of mid-log-phase culture. Nine type A strains had one or more plasmids of 4.3, 6.8, or 36 megadaltons (MDa); several strains showed a large plasmid of 61 MDa, but it was not consistently recovered. Four C. sporogenes strains had one or more plasmids of 4.3, 5.6 or 36 MDa. Isolates obtained from cultures of plasmid-containing C. botulinum type A strains grown in ionic detergent broth and from spontaneously arising variants were screened both for toxin production and for plasmid content. Toxigenicity of C. botulinum could not be correlated with the presence of any one plasmid.

Partial characterization of the genetic basis for sucrose metabolism and nisin production in Streptococcus lactis

We attempted to identify the genetic loci for sucrose-fermenting ability (Suc+), nisin-producing ability (Nip+), and nisin resistance (Nisr) in certain strains of Streptococcus lactis. To obtain genetic evidence linking the Suc+ Nip+ Nisr phenotype to a distinct plasmid, both conjugal transfer and transformation were attempted. A conjugation procedure modified to protect the recipients against the inhibitory action of nisin allowed the conjugal transfer of the Suc+ Nip+ Nisr marker from three Suc+ Nip+ Nisr donors to various recipients. The frequency of transfer ranged from 1.7 x 10(-4) to 5.6 x 10(-8) per input donor, depending on the mating pair. However, no additional plasmid DNA was apparent in these transconjugants. Transformation of S. lactis LM0230 to the Suc+ Nip+ Nisr phenotype by using the plasmid pool of S. lactis ATCC 11454 was not achieved, even though other plasmids present in the pool were successfully transferred. However, two results imply the involvement of plasmid DNA in coding for the Suc+ Nip+ Nisr phenotype. The Suc+ Nip+ Nisr marker was capable of conjugal transfer to a recipient deficient in host-mediated homologous recombination (Rec-), and the Suc+ Nip+ Nisr marker exhibited bilateral plasmid incompatibility with a number of lactose plasmids found in S. lactis. Although our results indicate that the Suc+ Nip+ Nisr phenotype is plasmid encoded, no physical evidence linking this phenotype to a distinct plasmid was obtained.

Transformation of Heat-Treated Clostridium acetobutylicum Protoplasts with pUB110 Plasmid DNA

Heat treatment of Clostridium acetobutylicum SA-1 protoplasts at 55°C for 15 min before transformation resulted in expression in this microorganism of the kanamycin resistance determinant associated with plasmid pUB110. No heat treatment, or heat treatment at 65 or 44°C for various time intervals, resulted in no kanamycin resistance transformants being recovered on selective kanamycin-containing regeneration medium. DNase plate assay indicated that treatment at 55°C for 15 min completely inactivated the DNase activity associated with SA-1 protoplasts. Treatment of protoplasts at 65 or 55°C for various periods under simulated transformation conditions had an inhibitory effect, although prolonged treatment at 55 or 44°C appeared to stimulate DNase activity. Inactivation of protoplast-associated DNase activity by heat treatment at 55°C for 15 min correlated with successful expression of kanamycin resistance and suggests that an extremely active, heatsensitive, protoplast-associated DNase may be a factor in the polyethylene glycol-induced transformation of C. acetobutylicum SA-1 protoplasts. Plasmid pUB110 DNA was isolated from C. acetobutylicum SA-1 kanamycin-resistant (Km r ) transformant cultures by a modification of the procedure used for C. perfringens plasmids. Detection of pUB110 DNA was possible only when diethyl pyrocarbonate was incorporated into isolation protocols to inactivate DNase activity. Restriction studies further verified the presence of pUB110 DNA in C. acetobutylicum SA-1 Km r transformants.