Carbon cycling: the prokaryotic contribution

Although the debate continues, the concept of global warming as a consequence of the increased production of 'greenhouse gases' via human activities is now widely accepted. The role of microbes, especially the prokaryotes, in the formation, trapping and retention of 'greenhouse gases' has, for the most part, been overlooked. The future requires that we pay close attention to these organisms for possible solutions to adverse global changes.

Cytochrome c(3) mutants of Desulfovibrio desulfuricans

To explore the physiological role of tetraheme cytochrome c(3) in the sulfate-reducing bacterium Desulfovibrio desulfuricans G20, the gene encoding the preapoprotein was cloned, sequenced, and mutated by plasmid insertion. The physical analysis of the DNA from the strain carrying the integrated plasmid showed that the insertion was successful. The growth rate of the mutant on lactate with sulfate was comparable to that of the wild type; however, mutant cultures did not achieve the same cell densities. Pyruvate, the oxidation product of lactate, served as a poor electron source for the mutant. Unexpectedly, the mutant was able to grow on hydrogen-sulfate medium. These data support a role for tetraheme cytochrome c(3) in the electron transport pathway from pyruvate to sulfate or sulfite in D. desulfuricans G20.

Transcriptional organization of the erythromycin biosynthetic gene cluster of Saccharopolyspora erythraea

The transcriptional organization of the erythromycin biosynthetic gene (ery) cluster of Saccharopolyspora erythraea has been examined by a variety of methods, including S1 nuclease protection assays, Northern blotting, Western blotting, and bioconversion analysis of erythromycin intermediates. The analysis was facilitated by the construction of novel mutants containing a S. erythraea transcriptional terminator within the eryAI, eryAIII, eryBIII, eryBIV, eryBV, eryBVI, eryCIV, and eryCVI genes and additionally by an eryAI -10 promoter mutant. All mutant strains demonstrated polar effects on the transcription of downstream ery biosynthetic genes. Our results demonstrate that the ery gene cluster contains four major polycistronic transcriptional units, the largest one extending approximately 35 kb from eryAI to eryG. Two overlapping polycistronic transcripts extending from eryBIV to eryBVII were identified. In addition, seven ery cluster promoter transcription start sites, one each beginning at eryAI, eryBI, eryBIII, eryBVI, and eryK and two beginning at eryBIV, were determined.

Keloids and hypertrophic scars

BACKGROUND

Keloids and hypertrophic scars are benign fibrous growths that occur after trauma or wounding of the skin and present a major therapeutic dilemma to the dermatologist because of frequent recurrences.

OBJECTIVE

The purpose of this study is to review the pertinent literature and provide updated information on keloids and hypertrophic scars that will enable the physician to better understand and treat these lesions.

METHODS

A Medline literature search was performed for relevant publications.

RESULTS

Traditional treatment methods which have been effective include a combination of surgery with intralesional steroids and/or radiotherapy, silicone gel sheeting, pressure, and cryotherapy. Recently newer modalities shown to be effective include pulsed dye laser, interferon alfa-2b, and cultured epithelial autografts.

CONCLUSION

Keloids and hypertrophic scars present a major therapeutic dilemma to the dermatologist because of frequent recurrences. A better understanding of keloid pathogenesis may lead to improved therapies by which keloid growth and regrowth may be obviated. Although optimal treatment for keloids remains undefined, successful treatment can be obtained through a multimodality approach. Regardless of the technique employed, an observation period of at least 2 years is necessary to rule out recurrence.

Sonication-dependent electroporation of the erythromycin-producing bacterium Saccharopolyspora erythraea

We report the development of an electrotransformation method applicable to all strains of Saccharopolyspora erythraea examined to date. Vegetatively grown mycelia were rendered electrocompetent by subjecting mycelial suspensions to ultrasound pulses. The protocol provides an alternative route for the introduction of DNA into filamentous microorganisms otherwise recalcitrant to transformation techniques.

Transposon mutagenesis in Desulfovibrio desulfuricans: development of a random mutagenesis tool from Tn7

The transposons Tn5, Tn7, Tn9, and Tn10 or their derivatives have been examined for transposition in the sulfate-reducing bacterium Desulfovibrio desulfuricans G20. Tn7 inserted with a frequency of 10(-4) to 10(-3) into a unique attachment site that shows strong homology with those sites identified in other gram-negative bacteria. Inactivation of the tnsD gene in Tn7, encoding the function directing insertion into the unique site, yielded a derivative that transposed essentially randomly with a frequency of ca. 10(-6) per donor. Derivatives of Tn5, but not wild-type Tn5, were also found to undergo random transposition at a similar frequency. No evidence was obtained for transposition of Tn9 or Tn10.

Use of Electroporation To Generate a Thiobacillus neapolitanus Carboxysome Mutant

Two cloning vectors designed for use in Escherichia coli and the thiobacilli were constructed by combining a Thiobacillus intermedius plasmid replicon with a multicloning site, lacZ(prm1), and either a kanamycin or a streptomycin resistance gene. Conditions necessary for the introduction of DNA into T. intermedius and T. neapolitanus via electroporation were examined and optimized. By using optimal electroporation conditions, the gene encoding a carboxysome shell protein, csoS1A, was insertionally inactivated in T. neapolitanus. The mutant showed a reduced number of carboxysomes and an increased level of CO(inf2) necessary for growth.

Isolation and characterization of the replicon of a Thiobacillus intermedius plasmid

The replicon of a cryptic Thiobacillus intermedius plasmid (pTiK12) has been isolated and sequenced. Functional analysis of deletion subclones in Escherichia coli localized the replicon to a 3.5-kb region of DNA. Sequencing of this region identified a 30-bp A-T-rich potential stem-loop structure. In addition, an 11-bp direct repeat, an 11-bp inverted repeat, and a 16-bp inverted repeat were observed at the stem-loop structure. Also found in the replicon was a series of four tandem direct repeats consisting of a perfectly conserved 8-bp core. A region near the stem-loop structure is involved in the regulation of plasmid copy number. Deletion subclones lacking this region have increased copy numbers, indicating a negative regulatory role. An open reading frame capable of encoding a 320-amino-acid protein was found near the stem-loop structure. The putative amino acid sequence shares significant similarity with the two Rep proteins from the ColE2 and ColE3 replicons. Replication of the T. intermedius replicon is dependent upon DNA polymerase I. The isolation and examination of the T. intermedius plasmid replicon are initial steps toward the establishment of a genetic system in T. intermedius.

Isolation and characterization of a carboxysome shell gene from Thiobacillus neapolitanus

The gene coding for the major carboxysome shell peptide (csoS1) from Thiobacillus neapolitanus has been isolated and sequenced. Oligonucleotide primers for polymerase chain reaction (PCR) amplification of the 5' end of the gene were made possible by amino acid sequencing of the N-terminal residues of the shell peptide. A 41 bp PCR product was used as a probe to isolate the gene. The deduced amino acid composition of the 216 bp gene shows a high degree of hydrophobicity. The gene is located within a series of three repeated regions of DNA and appears to have arisen via gene duplication. The transcript of csoS1 is approximately 400 bases in length. The shell peptide shares significant homology with Synechococcus open reading frames implicated in carboxysome structure/assembly. These open reading frames and csoS1 are related and are probably members of a carboxysome gene family.

Two forms of ribulose-1,5-bisphosphate carboxylase/oxygenase from Thiobacillus denitrificans

The autotrophic, sulfur-oxidizing bacterium Thiobacillus denitrificans possesses two forms of the Calvin cycle enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO). The form I and form II genes were isolated from a cosmid library using heterologous DNA probes. Restriction enzyme analysis indicated that the genes are within 17 kbp of each other. Other Calvin cycle enzyme genes are not present. Analysis of T. denitrificans RNA indicated that the form I genes for the large and small subunits are co-transcribed with a length of 2800 nucleotides. The transcript for the form II gene is 1900 nucleotides in length.

The carboxysome, a prokaryotic organelle: a mini-review

Since first being isolated and named carboxysomes more than 17 years ago, these prokaryotic inclusions have been studied with great interest. Several summary statements can be made regarding the structure, composition, and function of carboxysomes. The carboxysome is composed of 7–15 peptides, of which 3–5 are shell glycoproteins. The only enzyme demonstrated to be associated with the carboxysomes is ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). The carboxysome may be a dodecahedron or an icosahedron. The molecular weight of the carboxysomes from Thiobacillus neapolitanus is approximately 2.4 × 108. Rubisco may fill the carboxysome or line the inner surface of the shell. The carboxysome is active in CO2 fixation. The function of the carboxysome is related to the availability of CO2 to the cells. The molecular mechanisms of carboxysome function are not yet available. Key words: carboxysomes, review, ribulose-1,5-bisphosphate carboxylase/oxygenase, Rubisco, structure, composition.