Expression of the transposable lac operon Tn951 in Rhodopseudomonas sphaeroides

Overexpression and purification of cytochrome c oxidase from Rhodobacter sphaeroides

The aa3-type cytochrome c oxidase of Rhodobacter sphaeroides has been overexpressed up to seven fold over that in wild-type strains by engineering a multicopy plasmid with all the required oxidase genes and by establishing optimum growth conditions. The two operons containing the three structural genes and two assembly genes for cytochrome c oxidase were ligated into a pUC19 vector and reintroduced into several oxidase-deleted R. sphaeroides strains. Under conditions of relatively high pH and maximal aeration, high levels of expression were observed. A smaller expression vector, pBBR1MCS, and a fructose promoter (fruP)5 were found not to enhance cytochrome c oxidase expression in R. sphaeroides. An improved cytochrome c oxidase purification protocol is reported, which combines histidine elution from a nickel affinity column and anion-exchange chromatography, and results in a higher yield and purity than previously obtained.

Use of green fluorescent protein to tag and investigate gene expression in marine bacteria

Two broad-host-range vectors previously constructed for use in soil bacteria (A. G. Matthysse, S. Stretton, C. Dandie, N. C. McClure, and A. E. Goodman, FEMS Microbiol. Lett. 145:87-94, 1996) were assessed by epifluorescence microscopy for use in tagging three marine bacterial species. Expression of gfp could be visualized in Vibrio sp. strain S141 cells at uniform levels of intensity from either the lac or the npt-2 promoter, whereas expression of gfp could be visualized in Psychrobacter sp. strain SW5H cells at various levels of intensity only from the npt-2 promoter. Green fluorescent protein (GFP) fluorescence was not detected in the third species, Pseudoalteromonas sp. strain S91, when the gfp gene was expressed from either promoter. A new mini-Tn10-kan-gfp transposon was constructed to investigate further the possibilities of fluorescence tagging of marine bacteria. Insertion of mini-Tn10-kan-gfp generated random stable mutants at high frequencies with all three marine species. With this transposon, strongly and weakly expressed S91 promoters were isolated. Visualization of GFP by epifluorescence microscopy was markedly reduced when S91 (mini-Tn10-kan-gfp) cells were grown in rich medium compared to that when cells were grown in minimal medium. Mini-Tn10-kan-gfp was used to create an S91 chitinase-negative, GFP-positive mutant. Expression of the chi-gfp fusion was induced in cells exposed to N'-acetylglucosamine or attached to chitin particles. By laser scanning confocal microscopy, biofilms consisting of microcolonies of chi-negative, GFP+ S91 cells were found to be localized several microns from a natural chitin substratum. Tagging bacterial strains with GFP enables visualization of, as well as monitoring of gene expression in, living single cells in situ and in real time.

Activation of the lac genes of Tn951 by insertion sequences from Pseudomonas cepacia

We have identified three transposable gene-activating elements from Pseudomonas cepacia on the basis of their abilities to increase expression of the lac genes of the broad-host-range plasmid pGC91.14 (pRP1::Tn951). When introduced into auxotrophic derivatives of P. cepacia 249 (ATCC 17616), this plasmid failed to confer the ability to utilize lactose. The lac genes of Tn951 were poorly expressed in P. cepacia and were not induced by isopropyl-beta-D-thiogalactopyranoside. Lac+ variants of the pGC91.14-containing strains which formed beta-galactosidase at high constitutive levels as a consequence of transposition of insertion sequences from the P. cepacia genome to sites upstream of the lacZ gene of Tn951 were isolated. Certain of the elements also increased gene expression in other bacteria. For example, IS407 strongly activated the lacZ gene of Tn951 in Pseudomonas aeruginosa and Escherichia coli, and IS406 (but not IS407) did so in Zymomonas mobilis. The results indicate that IS elements from P. cepacia have potential for turning on the expression of foreign genes in a variety of gram-negative bacteria.

Salt tolerance of lactose-grown Vibrio parahaemolyticus carrying Escherichia coli lac genes

Lac- strains of Vibrio parahaemolyticus were converted to Lac+ on receiving a hybrid plasmid containing the lactose utilization genes of Escherichia coli K-12. A V. parahaemolyticus strain containing this hybrid plasmid exhibited optimal growth rates on glucose and other carbon sources in the presence of 0.2 to 0.4 M NaCl. Growth of the same strain on lactose was inhibited at similar concentrations of NaCl. The altered growth rate responses in lactose medium appeared to be attributable to effects of NaCl on the activity of lactose permease, and possibly on that of beta-galactosidase, rather than on the levels of these enzymes in V. parahaemolyticus cells.

Cloning, DNA sequence, and expression of the Rhodobacter sphaeroides cytochrome c2 gene

The Rhodobacter sphaeroides cytochrome c2 functions as a mobile electron carrier in both aerobic and photosynthetic electron transport chains. Synthetic deoxyoligonucleotide probes, based on the known amino acid sequence of this protein (Mr 14,000), were used to identify and clone the cytochrome c2 structural gene (cycA). DNA sequence analysis of the cycA gene indicated the presence of a typical procaryotic 21-residue signal sequence, suggesting that this periplasmic protein is synthesized in vivo as a precursor. Synthesis of an immunoreactive cytochrome c2 precursor protein (Mr 15,500) was observed in vitro when plasmids containing the cycA gene were used as templates in an R. sphaeroides coupled transcription-translation system. Approximately 500 base pairs of DNA upstream of the cycA gene was sufficient to allow expression of this gene product in vitro. Northern blot analysis with an internal cycA-specific probe identified at least two possibly monocistronic transcripts present in both different cellular levels and relative stoichiometries in steady-state cells grown under different physiological conditions. The ratio of the small (740-nucleotide) and large (920-nucleotide) cycA-specific mRNA species was dependent on cultural conditions but was not affected by light intensity under photosynthetic conditions. Our results suggest that the increase in the cellular level of the cytochrome c2 protein found in photosynthetic cells was due, in part, to increased transcription of the single-copy cyc operon.

Cloning and expression of the Rhodobacter sphaeroides reaction center H gene

The Rhodobacter sphaeroides structural gene (puhA) for the reaction center H polypeptide has been identified and cloned by using restriction fragements specific for the analogous Rhodobacter capsulatus gene as a heterologous hybridization probe. The presence of puhA on a 1.45-kilobase BamHI restriction fragment was confirmed by partial DNA sequence analysis and by the synthesis of an immunoreactive Mr-28,000 reaction center H polypeptide in an R. sphaeroides coupled transcription-translation system. Approximately 450 base pairs of DNA upstream of the puhA gene were sufficient for expression of this protein in vitro. Northern RNA-DNA blot analysis with an internal puhA-specific probe identified at least two, apparently monocistronic, transcripts present at different cellular levels under physiological conditions known to affect the cellular content of both reaction center complexes and photosynthetic membrane. Northern blot analysis with specific upstream restriction fragment probes revealed that the 1,400-nucleotide puhA-specific mRNA had a 5' terminus upstream of the 1,130-nucleotide transcript. Both puhA-specific mRNA and immunoreactive reaction center H protein were detectable in chemoheterotrophically grown cells which lacked detectable bacteriochlorophyll and photosynthetic membrane.

Measurement of the proton motive force in Rhizobium meliloti with the Escherichia coli lacY gene product

An Escherichia coli lac operon constitutive for lacY was subcloned into the EcoRI site of a wide-host-range plasmid of the Q incompatibility group, and the resulting recombinant plasmid was introduced into Tn5-generated Lac- mutants of Rhizobium meliloti. The R. meliloti transconjugants accumulated lactose about 1,000-fold, equivalent to a proton motive force of -170 to -180 mV, not significantly different from the values calculated from the distributions of weak acids and lipophilic cations.

Intracellular localization of phospholipid transfer activity in Rhodopseudomonas sphaeroides and a possible role in membrane biogenesis

The cellular content of phospholipid transfer activity in Rhodopseudomonas sphaeroides was examined as a function of both oxygen partial pressure and light intensity used for growth. Cells grown under high light conditions (100 W/m2) had over two times the cellular level of phospholipid transfer activity when compared with cells grown under other conditions. Although cells grown under low light conditions (3 W/m2) had the lowest amount of total phospholipid transfer activity, they had the highest level (49%) of membrane-associated transfer activity. The soluble phospholipid transfer activity was further localized into periplasmic and cytoplasmic fractions. The distribution of phospholipid transfer activity in cells grown under medium light intensity (10 W/m2) was calculated as 15.1% membrane-associated, 32.4% in the periplasm, and 52.5% in the cytoplasm. The phospholipid transfer activities in the periplasmic and cytoplasmic fractions had distinctly different properties with respect to their molecular weights (56,000 versus 27,000) and specificities of transfer (phosphatidylethanolamine greater than phosphatidylglycerol versus phosphatidylglycerol greater than phosphatidylethanolamine).

Broad-host-range plasmid vector for the in vitro construction of transcriptional/translational lac fusions

A broad-host-range plasmid was constructed that allows the in vitro formation of beta-galactosidase fusions. DNA from the photosynthetic bacterium Rhodopseudomonas sphaeroides was cloned into this plasmid and a number of R. sphaeroides isolates were recovered that had varying levels of beta-galactosidase activity. beta-galactosidase antigenic activity from the fusion strains could be localized immunologically in polypeptides with an Mr of 120 000 or greater. Expression of beta-galactosidase activity under control of fusion derivatives was either very low or nonexistent in Escherichia coli relative to R. sphaeroides, indicating that R. sphaeroides promoters or translational start signals function poorly in E. coli.

Plasmid rearrangements in the photosynthetic bacterium Rhodopseudomonas sphaeroides

Mu d1(Ap lac) was introduced into the photosynthetic bacterium Rhodopseudomonas sphaeroides 2.4.1. via the R-plasmid R751 in an attempt to isolate fusion derivatives involving photosynthetic operons. The selection system is potentially very powerful since R. sphaeroides is normally Lac negative. Among the exconjugants, photosynthesis-deficient mutants were recovered, some of which had elevated beta-galactosidase levels. Among the mutants examined, beta-galactosidase expression was linked exclusively to R751 . Many of the photosynthesis-deficient mutants were found to have alterations in their indigenous plasmids which apparently involved the exchange of DNA from one plasmid to another. Southern blot analysis revealed that there are extensive DNA sequences which are shared by the two plasmids that are involved in the rearrangements and that no exogenous DNA sequences appear to be involved. It was further discovered that plasmid rearrangement is a general phenomenon which can occur spontaneously in R. sphaeroides 2.4.1 and shows a high correlation with a photosynthesis minus phenotype.

Expression of a Lactose Transposon (Tn 951 ) in Zymomonas mobilis

The potential utility of Zymomonas mobilis as an organism for the commercial production of ethanol would be greatly enhanced by the addition of foreign genes which expand its range of fermentable substrates. We tested various plasmids and mobilizing factors for their ability to act as vectors and introduce foreign genes into Z. mobilis CP4. Plasmid pGC91.14, a derivative of RP1, was found to be transferred from Escherichia coli to Z. mobilis at a higher frequency than previously reported for any other plasmids. Both tetracycline resistance and the lactose operon from this plasmid were expressed in Z. mobilis CP4. Plasmid pGC91.14 was stably maintained in Z. mobilis at 30°C but rapidly lost at 37°C.

Transcriptional regulation of several genes for bacteriochlorophyll biosynthesis in Rhodopseudomonas capsulata in response to oxygen

Although it has been shown that bacteriochlorophyll synthesis in Rhodopseudomonas capsulata is repressed by oxygen and high light intensity, few details of regulation by these environmental factors are known, primarily owing to a lack of assays for the biosynthetic enzymes. We have examined regulation at the transcriptional level by isolating and studying fusions between the Mu d1(Apr lac) phage and various bch genes. In these strains, the lacZ gene of the phage is under the control of bch gene promoters. We have found that atmospheric oxygen tension (20% O2) reduces the expression of these fusions at least twofold compared with low oxygen tension (2% O2). Therefore, transcription of the bchA, bchB, bchC, bchG, and bchH genes is regulated in response to oxygen.