Synthesis of cell envelope components by anucleate cells (minicells) of Bacillus subtilis

Following the fate of bacterial cells experiencing sudden chromosome loss

Chromosomal DNA is a constant source of information, essential for any given cell to respond and adapt to changing conditions. Here, we investigated the fate of exponentially growing bacterial cells experiencing a sudden and rapid loss of their entire chromosome. Utilizing Bacillus subtilis cells harboring an inducible copy of the endogenous toxin yqcG, which encodes an endonuclease, we induced the formation of a population of cells that lost their genetic information simultaneously. Surprisingly, these DNA-less cells, termed DLCs, did not lyse immediately and exhibited normal cellular morphology for a period of at least 5 h after DNA loss. This cellular integrity was manifested by their capacity to maintain an intact membrane and membrane potential and cell wall architecture similar to those of wild-type cells. Unlike growing cells that exhibit a dynamic profile of macromolecules, DLCs displayed steady protein and RNA reservoirs. Remarkably, following DLCs by time lapse microscopy revealed that they succeeded in synthesizing proteins, elongating, and dividing, apparently forming de novo Z rings at the midcell position. Taken together, the persistence of key cellular events in DLCs indicates that the information to carry out lengthy processes is harbored within the remaining molecular components.

IMPORTANCE

Perturbing bacterial growth by the use of antibiotics targeting replication, transcription, or translation has been a subject of study for many years; however, the consequences of a more dramatic event, in which the entire bacterial chromosome is lost, have not been described. Here, we followed the fate of bacterial cells encountering an abrupt loss of their entire genome. Surprisingly, the cells preserved an intact envelope and functioning macromolecules. Furthermore, cells lacking their genome could still elongate and divide hours after the loss of DNA. Our data suggest that the information stored in the transient reservoir of macromolecules is sufficient to carry out complex and lengthy processes even in the absence of the chromosome. Based on our study, the formation of DNA-less bacteria could serve as a novel vaccination strategy, enabling an efficient induction of the immune system without the risk of bacterial propagation within the host.

The chloroplast beta-subunit allows assembly of the Escherichia coli F0 portion of the energy transducing adenosine triphosphatase

The effect of the expression of the chloroplast F1-ATPase beta-subunit in two Escherichia coli beta-subunit mutant strains was investigated. The amount of chloroplast beta-subunit formed in E. coli was increased by introducing a 'Shine-Dalgarno' sequence upstream from the translation start site. The chloroplast beta-subunit was membrane bound but was unable to functionally replace the mutant beta-subunit in a strain carrying the uncD409 allele [corrected]. However, in an E. coli mutant strain unable to form the beta- and epsilon-subunits the presence of the chloroplast beta-subunit enabled the assembly of a functional proton pore [corrected]

Replication genes of plasmid pE194-cop and repF: transcripts and encoded proteins

In vivo transcription of the replication region of plasmid pE194 yeidls two classes of mRNAs that encode Cop and RepF proteins, respectively. These transcripts are oriented 5' to 3' exclusively in the clockwise direction on the standard map. The cop region contains an open reading frame capable of encoding a 55-amino-acid protein that was demonstrated electrophoretically as a 6-kilodalton product synthesized in Bacillus subtilis minicells and chemically by N-terminal sequencing of a 116-kilodalton fusion protein with Escherichia coli beta-galactosidase. Four transcripts derived from the repF region were found, of which the longest, approximately 720 nucleotides, had the length, orientation, and transcription start site necessary to code for the full-length RepF protein (216 amino acid residues), deduced from the DNA sequence. The 5' ends of the shorter repF transcripts fall within the repF open reading frame. We propose that (i) cop specifies a protein rather than an RNA countertranscript, (ii) the Cop protein functions as a negative-acting element in pE194 replication by regulating synthesis of both RepF and of itself, and (iii) increased plasmid copy number can be explained in terms of cop region mutations that either reduce the intrinsic activity of Cop protein or the rate of its synthesis.

Expression of coliphage T7 in aging anucleate minicells of Escherichia coli

Anucleate minicells produced by a mutated strain of Escherichia coli remain metabolically active for up to 48 h at 37 degrees C. Minicells of increasing age have been infected with the coliphage T7. Infection results in the onset of transcription and translation producing T7 encoded polypeptides. Quantitative and qualitative changes in T7 gene expression result from infection of increasingly old minicells. There is no detectable increase in the frequency of error occurrence in the synthesis of T7 polypeptides in infected old minicells as compared to infected young minicells.

Post-transcriptional regulation of chloramphenicol acetyl transferase

The +1 site for initiation of inducible chloramphenicol acetyl transferase (CAT) mRNA encoded by plasmid pC194 was determined experimentally by using [alpha-32P]ATP-labeled runoff transcripts partially digested with T1 RNase. By partial digestion of the in vitro transcripts with S1, T1, and cobra venom nucleases as probes of mRNA conformation, single- and double-stranded regions, respectively, were also identified. Thus, a prominent inverted complementary repeat sequence was demonstrated spanning the +14 to +50 positions, which contain the complementary sequences CCUCC and GGAGG (the Shine and Dalgarno sequence for synthesis of CAT) symmetrically apposed and paired as part of a perfect 12-base-pair inverted complementary repeat sequence (-19.5 kcal [ca. -81.7 kJ] per mol). The CAT mRNA was stable to digestion by T1 RNase at the four guanosine residues in the Shine and Dalgarno sequence GGAGG , even at 60 degrees C, suggesting that nascent CAT mRNA allows ribosomes to initiate protein synthesis inefficiently and that induction involves post-transcriptional unmasking of the Shine and Dalgarno sequence. Consistent with this model of regulation, we found that cells carrying pC194 , induced with chloramphenicol, contain about the same concentration of pulse-labeled CAT-specific RNA as do uninduced cells. Induction of CAT synthesis by the non- acetylatable chloramphenicol analog fluorothiamphenicol was tested by using minicells of Bacillus subtilis carrying pC194 as well as minicells containing the cloned pC194 derivatives in which parts of the CAT structural gene were deleted in vitro with BAL 31 exonuclease. Optimal induction of both full-length (active) and deleted (inactive) CAT required similar concentrations of fluorothiamphenicol, whereas induction by chloramphenicol required a higher concentration for the wild-type full-length (active) CAT than for the (inactive) deleted CAT. Because synthesis of deleted CAT was inducible, we infer that CAT plays no direct role in regulating its own synthesis.

Cloning and expression of the phage Mu A gene

We have cloned the phage Mu A gene, with and without the gene ner, under the control of the pL promoter of phage lambda in a multicopy plasmid vector. We demonstrate that plasmid-carrying cells are able to support growth of superinfecting Mu A am phages in a temperature-dependent fashion in a host strain carrying a defective lambda prophage which specifies the cI857-coded lambda repressor. In addition, we show that the presence of the ner gene reduces the efficiency of plating of the superinfecting phage. Analysis of proteins specified by the cloned Mu fragments indicates that two proteins, 70 and 33 kDal, are synthesized. The level of synthesis, compared to that of the vector-encoded beta-lactamase, was found to increase with temperature. This indicates that their transcription is driven by the pL promoter. The Mr of the 70-kDal protein is identical to that previously observed for pA.

Synthesis of yeast histone 3 in an Escherichia coli cell-free system

The gene for histone H3 from the yeast Saccharomyces cerevisiae was placed under the control of the lac promoter of Escherichia coli by fusing the H3 coding sequence to that of beta-galactosidase. The gene was shown to be transcribed in vivo, but its product was not detected in cell extracts. However, synthesis of the fused polypeptide was detected in an in vitro transcription-translation system derived from E. coli. Proteolytic degradation of the newly synthesized polypeptides may be the cause of their apparent absence in the in vivo experiment.

A complex attenuator regulates inducible resistance to macrolides, lincosamides, and streptogramin type B antibiotics in Streptococcus sanguis

Macrolide-lincosamide-streptogramin B resistance specified by Streptococcus sanguis plasmid pAM77 involves an adenine methylase, whose synthesis, demonstrable both phenotypically and by analysis of methionine-labeled proteins made in Bacillus subtilis minicells, is inducible by erythromycin, lincomycin, and streptogramin type B antibiotics. Localization of the methylase structural gene, including its control region in DNA fragments obtained with restriction endonucleases, has been deduced from DNA blot experiments with characterized target and probe DNAs from other streptococci, combined with DNA sequence analysis and comparison of the putative streptococcal methylase sequence with that of a cognate methylase in staphylococcal plasmid pE194. The streptococcal methylase migrates electrophoretically in polyacrylamide gels with the mobility of a 29,000-dalton protein. The sequence organization of the putative streptococcal methylase mRNA leader sequence partially resembles its staphylococcal counterpart and can support a similar mechanism of secondary structure rearrangement leading to methylase synthesis. The deduced 5' leader sequence preceding the pAM77 methylase structural gene sequence comprises approximately 155 nucleotides within which one can identify a putative control peptide 36 amino acid residues in length (in contrast to 19 in the pE194 peptide) and at least 14 possible classes of overlapping inverted complementary repeat sequences (in contrast to 3 in the pE194 control region), one of which can sequester the sequence AGGAG 7 nucleotides upstream from the putative (methionine) start codon of the streptococcal methylase. Comparison of the pAM77 and pE194 methylase amino acid sequences and their respective nucleotide sequences shows 51% conservation of amino acid residues (124 of 244) and 59% conservation of nucleotide residues (433 of 738), which suggests a common origin for the two methylase structural gene sequences. Differences in mRNA base composition associated with conserved amino acid residues occur mostly in the third nucleotide ("wobble") position of codons and may reflect adaptation of methylase genes to optimal expression in host cells with differing codon use patterns.

Hepatitis B virus core antigen: synthesis in Escherichia coli and application in diagnosis

Fragments of hepatitis B virus DNA cloned in plasmid pBR322 carrying the gene for the viral core antigen have been placed under the control of the lac promoter of Escherichia coli. Several of the new recombinants direct higher levels of synthesis of the antigen, but the degree of enhancement varies with the different structures of the plasmids and hence the mRNAs produced. The antigen in crude bacterial lysates is a satisfactory diagnostic reagent for antibodies to the core antigen in serum samples.

Cloning of bacteriophage T5 DNA fragments. III. Expression in Escherichia coli mini-cells

Use has been made of the mini-cell system to study polypeptide synthesis from cloned EcoRI, HindIII and PstI fragments of T5 DNA. The correlation of certain gene products with known genes has been established, as well as the physical mapping of genes not yet identified genetically. In some cases, it has been possible to demonstrate the presence of T5 promoters on the cloned DNA fragments. The design of experiments to avoid certain artifacts inherent in the use of the mini-cell system is discussed.

Cloning and expression of Bacillus subtilis phage SPP1 in E. coli. II. Expression of lambda/SPP1 hybrid phages in E. coli minicells

In the preceding paper (Amann et al. 1981) we described the in vitro construction of hybrids between Escherichia coli phage lambda NM607 imm434 and B. subtilis phage SPP1. These lambda/SPP1 hybrids have been used to infect minicells produced by E. coli strain DS410. Analysis on polyacrylamide gels of 35S-methionine labeled proteins synthesized in infected minicells revealed the expression of both lambda and SPP1 genes. Infection of E. coli minicells carrying plasmid pGY101, which encodes and expresses the repressor gene of phage 434, results in the selective expression of the cloned SPP1 DNA. This has resulted in the assignment of 26 out of a total of 46 known SPP1 polypeptides (Mertens et al. 1979) to individual SPP1 DNA fragments. In addition, several lambda/SPP1 fusion peptides whose transcription either originates from lambda promoters or from promoters located on the inserted SPP1 fragment, were identified.

An IS4-encoded protein is synthesized in minicells

A protein of Mr 47,000 is synthesized in Escherichia coli minicells, when these harbor a multicopy plasmid carrying IS4 in either orientation and between different flanking sequences. The protein corresponds to the sequence predicted from the known DNA sequence of IS4, as shown by partial N-terminal radiolabel protein sequence analysis. Its apparent molecular weight, however, as determined from its electrophoretic mobility in SDS polyacrylamide gels, is smaller than predicted. When compared with other plasmid-encoded proteins, the IS4-encoded protein is synthesized in minicells in small amounts. Its synthesis has not been detected in a DNA-dependent cell-free system.

Target cell specificity of two species of human interferon-alpha produced in Escherichia coli and of hybrid molecules derived from them

Plasmids containing cDNAs for human interferon (IfN) alpha-1, IFN alpha-2, and several hybrids of the two cDNAs, all joined identically to an Escherichia coli lac promoter fragment gave rise, in E. coli, to fused interferons (fIFNs) that had very different target-cell specificities. fIFN alpha-1 had a lower specific activity on human WISH cells than on bovine MDBK cells, while fIFN alpha-2 showed the opposite behavior. fIFN hybrids with the NH2-proximal half of fIFN alpha-2 behaved qualitatively like fIFN alpha-1, and those with the NH2-proximal half of fIFN alpha-2, behaved like fIFN alpha-2. On mouse L929 cells, fIFN alpha-2 was almost inactive, while fIFN alpha-1 showed relatively high activity. In this case, the fIFN hybrids with the COOH-proximal half of IFN alpha-1 showed activity on mouse cells, while the reciprocal hybrid did not. In many cases, the activity spectrum of the hybrids was very different from that of either parent. We propose that the IFN molecule has either two binding sites or two regions constituting the binding site, one in the COOH- and the other in the NH2-proximal half. The experimental findings can be accounted for if the fits of the two sites to their receptor counterparts on different cell lines are independent of one another.

Bacteriophage phi 29 infection of Bacillus subtilis minicells

Bacteriophage phi 29 can infect B. subtilis minicells and synthesize all the phage-coded proteins detected in ultraviolet irradiated-infected B. subtilis cells. Synthesis of phage unit-length DNA has been obtained after infection of minicells with phi 29. The DNA can be encapsulated in particles with a sedimentation rate similar to that of phage phi 29 produced in B. subtilis cells. The particles produced in minicells can be adsorbed to B. subtilis cells, but infectivity has not been demonstrated because of the very low burst-size obtained.

Cloning of the structural gene (ompA) for an integral outer membrane protein of Escherichia coli K-12

The gene (ompA) for the major outer membrane protein II* from Escherichia coli K-12 has been cloned on a 5-megadalton EcoRI fragment by using phage lambda as vector. The gene is expressed during the lytic cycle of the recombinant phage and the insoluble membrane-bound protein was detected in phage plaques with a simple radioimmunoassay. Transfer of the EcoRI fragment into plasmid pSC101 and expression in a host lacking protein II* led to overproduction of protein II* and decreased production of two other major outer membrane proteins. Expression of the plasmid pSC101-ompA+ in minicells derived from an ompA minicell-producing strain led to synthesis, at high rates, of this protein and massive accumulation of a second cell envelope protein most likely representing the biosynthetic precursor of protein II*.

Lambda encodes an outer membrane protein: the lom gene

lambda infected minicells synthesize a polypeptide (M(r) = 20,500) which is incorporated almost exclusively into the outer membrane of the minicell envelope. The gene (lom = lambda outer membrane) encoding this polypeptide has been mapped in the non-essential region of the lambda genome between coordinates 39.4% and 40.7% of lambda.

Bacteriophage SPP1 polypeptides synthesized in infected minicells and in vitro

Minicells produced by B. subtilis CU403divIVB1 and infected by SPP1 synthesize at least 46 polypeptides which can be separated by polyacrylamide gel electrophoresis. These polypeptides represent the expression of 86% of the SPP1 genome's coding capacity. Infection of minicells by sus mutants and deletion mutants of SPP1 has permitted a correlation of genetic location with gene product and has shown that SPP1 normally synthesizes at least 8 non-essential polypeptides. Restriction fragments of SPP1 produced by EcoRI digestion of SPP1 DNA have been purified and used as template DNA in a coupled transcription/translation system derived from E. coli to determine the polypeptides encoded by the individual fragments. SPP1 expression in minicells differs from SPP1 expression in nucleated cells (Esche, 1975) in that late syntheses are not dependent on phage DNA replication in infected minicells.

DNA synthesis in toluene-treated bacteriophage-infected minicells or Bacillus subtilis

Bateriophage (phi29, SPP1, or SPO1)-infected, toluene-treated minicells of Bacillus subtilis are capable of limited amounts of non-replicative DNA synthesis as measured by incorporation of [3H]dTTP into a trichloroacetic acid-precipitable form. The [3H]dTTP is covalently incorporated into small DNA fragments which result from the degradation of a small percentage of the infecting phage genomes (molecular weights in the range of 2 . 10(5)). Short exposure of the DNA molecules containing the incorporated [3H]dTMP to Escherichia coli exonuclease III results in over 90% of the E13H]dTMP being converted to a trichloroacetic acid-soluble form. The synthesis is totally dependent on host-cell enzymes and is not inhibited by the addition of chloramphenicol, rifampicin, nalidixic acid and mitomycin C and only slightly (approx. 20%) inhibited by the addition of 6-(p-hydroxyphenylazo)-uracil.

Mucopeptide biosynthesis by minicells of Escherichia coli

Minicells produced by Escherichia coli chi925 incorporated amino acids and N-acetyl-d-glucosamine into mucopeptide.