Isolation and physical characterization of plasmid pCCl from Corynebacterium callunae and construction of hybrid derivatives

Isolation and characterization of a heavy metal- and antibiotic-tolerant novel bacterial strain from a contaminated culture plate of Chlamydomonas reinhardtii, a green micro-alga

Background:Chlamydomonas reinhardtii, a green micro-alga, is normally cultured in laboratories in Tris-Acetate Phosphate (TAP), a medium which contains acetate as the sole carbon source. Acetate in TAP can lead to occasional bacterial and fungal contamination. We isolated a yellow-pigmented bacterium from a Chlamydomonas TAP plate. It was named Clip185 based on the Chlamydomonas strain plate it was isolated from. In this article we present our work on the isolation, taxonomic identification and physiological and biochemical characterizations of Clip185. Methods: We measured sensitivities of Clip185 to five antibiotics and performed standard microbiological tests to characterize it. We partially sequenced the 16S rRNA gene of Clip185. We identified the yellow pigment of Clip185 by spectrophotometric analyses. We tested tolerance of Clip185 to six heavy metals by monitoring its growth on Lysogeny Broth (LB) media plates containing 0.5 mM -10 mM concentrations of six different heavy metals. Results: Clip185 is an aerobic, gram-positive rod, oxidase-negative, mesophilic, alpha-hemolytic bacterium. It can ferment glucose, sucrose and mannitol. It is starch hydrolysis-positive. It is very sensitive to vancomycin but resistant to penicillin and other bacterial cell membrane- and protein synthesis-disrupting antibiotics. Clip185 produces a C50 carotenoid, decaprenoxanthin, which is a powerful anti-oxidant with a commercial demand. Decaprenoxanthin production is induced in Clip185 under light. NCBI-BLAST analyses of the partial 16S rRNA gene sequence of Clip185 revealed a 99% sequence identity to that of Microbacterium binotii strain PK1-12M and Microbacterium sp. strain MDP6. Clip185 is able to tolerate toxic concentrations of six heavy metals. Conclusions: Our results show that Clip185 belongs to the genus Microbacterium. In the future, whole genome sequencing of Clip185 will clarify if Clip185 is a new Microbacterium species or a novel strain of Microbacterium binotii, and will reveal its genes involved in antibiotic-resistance, heavy-metal tolerance and regulation of decaprenoxanthin biosynthesis.

Isolation and characterization of a heavy metal- and antibiotic-tolerant novel bacterial strain from a contaminated culture plate of Chlamydomonas reinhardtii, a green micro-alga

Background:Chlamydomonas reinhardtii, a green micro-alga, is normally cultured in laboratories in Tris-Acetate Phosphate (TAP), a medium which contains acetate as the sole carbon source. Acetate in TAP can lead to occasional bacterial and fungal contamination. We isolated a yellow-pigmented bacterium from a Chlamydomonas TAP plate. It was named Clip185 based on the Chlamydomonas strain plate it was isolated from. In this article we present our work on the isolation, taxonomic identification and physiological and biochemical characterizations of Clip185. Methods: We measured sensitivities of Clip185 to five antibiotics and performed standard microbiological tests to characterize it. We partially sequenced the 16S rRNA gene of Clip185. We identified the yellow pigment of Clip185 by spectrophotometric analyses. We tested tolerance of Clip185 to six heavy metals by monitoring its growth on Lysogeny Broth (LB) media plates containing 0.5 mM -10 mM concentrations of six different heavy metals. Results: Clip185 is an aerobic, gram-positive rod, oxidase-negative, mesophilic, alpha-hemolytic bacterium. It can ferment glucose, sucrose and mannitol. It is starch hydrolysis-positive. It is very sensitive to vancomycin but resistant to penicillin and other bacterial cell membrane- and protein synthesis-disrupting antibiotics. Clip185 produces a C50 carotenoid, decaprenoxanthin, which is a powerful anti-oxidant with a commercial demand. Decaprenoxanthin production is induced in Clip185 under light. NCBI-BLAST analyses of the partial 16S rRNA gene sequence of Clip185 revealed a 99% sequence identity to that of Microbacterium binotii strain PK1-12M and Microbacterium sp. strain MDP6. Clip185 is able to tolerate toxic concentrations of six heavy metals. Conclusions: Our results show that Clip185 belongs to the genus Microbacterium. In the future, whole genome sequencing of Clip185 will clarify if Clip185 is a new Microbacterium species or a novel strain of Microbacterium binotii, and will reveal its genes involved in antibiotic-resistance, heavy-metal tolerance and regulation of decaprenoxanthin biosynthesis.

Isoprenoid Pyrophosphate-Dependent Transcriptional Regulation of Carotenogenesis in Corynebacterium glutamicum

Corynebacterium glutamicum is a natural producer of the C50 carotenoid decaprenoxanthin. The crtEcg0722crtBIYEb operon comprises most of its genes for terpenoid biosynthesis. The MarR-type regulator encoded upstream and in divergent orientation of the carotenoid biosynthesis operon has not yet been characterized. This regulator, named CrtR in this study, is encoded in many actinobacterial genomes co-occurring with terpenoid biosynthesis genes. CrtR was shown to repress the crt operon of C. glutamicum since DNA microarray experiments revealed that transcript levels of crt operon genes were increased 10 to 70-fold in its absence. Transcriptional fusions of a promoter-less gfp gene with the crt operon and crtR promoters confirmed that CrtR represses its own gene and the crt operon. Gel mobility shift assays with purified His-tagged CrtR showed that CrtR binds to a region overlapping with the −10 and −35 promoter sequences of the crt operon. Isoprenoid pyrophosphates interfered with binding of CrtR to its target DNA, a so far unknown mechanism for regulation of carotenogenesis. The molecular details of protein-ligand interactions remain to be studied. Decaprenoxanthin synthesis by C. glutamicum wild type was enhanced 10 to 30-fold upon deletion of crtR and was decreased 5 to 6-fold as result of crtR overexpression. Moreover, deletion of crtR was shown as metabolic engineering strategy to improve production of native and non-native carotenoids including lycopene, β-carotene, C.p. 450 and sarcinaxanthin.

Production and glucosylation of C50 and C 40 carotenoids by metabolically engineered Corynebacterium glutamicum

The yellow-pigmented soil bacterium Corynebacterium glutamicum ATCC13032 is accumulating the cyclic C50 carotenoid decaprenoxanthin and its glucosides. Carotenoid pathway engineering was previously shown to allow for efficient lycopene production. Here, engineering of C. glutamicum for production of endogenous decaprenoxanthin as well as of the heterologous C50 carotenoids C.p.450 and sarcinaxanthin is described. Plasmid-borne overexpression of genes for lycopene cyclization and hydroxylation from C. glutamicum, Dietzia sp., and Micrococcus luteus, in a lycopene-producing platform strain constructed here, resulted in accumulation of these three C50 carotenoids to concentrations of about 3-4 mg/g CDW. Chromosomal deletion of a putative carotenoid glycosyltransferase gene cg0730/crtX in these strains entailed production of non-glucosylated derivatives of decaprenoxanthin, C.p.450, and sarcinaxanthin, respectively. Upon introduction of glucosyltransferase genes from M. luteus, C. glutamicum, and Pantoea ananatis, these hydroxylated C50 carotenoids were glucosylated. We here also demonstrate production of the C40 carotenoids β-carotene and zeaxanthin in recombinant C. glutamicum strains and co-expression of the P. ananatis crtX gene was used to obtain glucosylated zeaxanthin. Together, our results show that C. glutamicum is a potentially valuable host for production of a wide range of glucosylated C40 and C50 carotenoids.

Characterization of broad host range cryptic plasmid pCR1 from Corynebacterium renale

Plasmid pCR1 is a cryptic plasmid harboured by Corynebacterium renale. It is the smallest corynebacterial plasmid known to date. Although its natural host is animal corynebacteria, it can replicate in several strains of soil corynebacteria. It can also replicate in Escherichia coli, in which it is stably maintained. The copy number of pCR1 in this host is higher than that of pUC19, with which it shows unidirectional incompatibility. It is also incompatible with pBK2, a plasmid bearing the common corynebacterial replicon pBL1. Its size is 1488bp, as revealed by DNA sequencing. A total of eight open reading frames (ORF) were detected in this plasmid, the largest of which codes for a putative Rep protein of predicted molecular mass of 21kDa. The plasmid pCR1 can be mobilized by the plasmid R6K from E. coli to other corynebacteria. Sequence analysis revealed the presence of an oriT homologous to that of R64. An E. coli plasmid pKL1 shows more than 90% identity with pCR1. Like many coryenbacterial plasmids, pCR1 also replicates by rolling circle mode.

Gene expression systems in corynebacteria

Corynebacterium belongs to a group of gram-positive bacteria having moderate to high G+C content, the other members being Mycobacterium, Nocardia, and Rhodococcus. Considerable information is now available on the plasmids, gene regulatory elements, and gene expression in corynebacteria, especially in soil corynebacteria such as Corynebacterium glutamicum. These bacteria are non-pathogenic and, unlike Bacillus and Streptomyces, are low in proteolytic activity and thus have the potential of becoming attractive systems for expression of heterologous proteins. This review discusses recent advances in our understanding of the organization of various regulatory elements, such as promoters, transcription terminators, and development of vectors for cloning and gene expression.

Characterization of the cryptic plasmid pCC1 from Corynebacterium callunae and its use for vector construction

The complete nucleotide sequence of the cryptic plasmid pCC1 from Corynebacterium callunae (4109 bp) was determined. DNA sequence analysis revealed five open reading frames longer than 200 bp. One of the deduced polypeptides showed homology with the Rep proteins encoded by plasmids of the pIJ101/pJV1 family of plasmids replicating by the rolling-circle (RC) mechanism. Within this plasmid family, the Rep protein of pCC1 showed the highest degree of similarity to the Rep proteins of corynebacterial plasmids pAG3 and pBL1. These data suggest that the plasmid pCC1 replicates by the RC mechanism. The Escherichia coli/Corynebacterium glutamicum shuttle cloning vector pSCCD1, carrying the pCC1 rep gene on the 2.1-kb DNA fragment and the streptomycin/spectinomycin resistance determinant, was constructed. This vector is stably maintained in population of C. glutamicum cells grown in the absence of selection pressure and it is compatible with plasmid vectors based on corynebacterial plasmids pBL1 and pSR1.

Recent advances in the physiology and genetics of amino acid-producing bacteria

Corynebacterium glutamicum and its close relatives, C. flavum and C. lactofermentum, have been used for over 3 decades in the industrial production of amino acids by fermentation. Since 1984, several research groups have started programs to develop metabolic engineering principles for amino acid-producing Corynebacterium strains. Initially, the programs concentrated on the isolation of genes encoding (deregulated) biosynthetic enzymes and the development of general molecular biology tools such as cloning vectors and DNA transfer methods. With most of the genes and tools now available, recombinant DNA technology can be applied in strain improvement. To accomplish these improvements, it is critical and advantageous to understand the mechanisms of gene expression and regulation as well as the biochemistry and physiology of the species being engineered. This review explores the advances made in the understanding and application of amino acid-producing bacteria in the early 1990s.

Characterization of pGA1, a new plasmid from Corynebacterium glutamicum LP-6

A new plasmid, pGA1, has been isolated from Corynebacterium glutamicum LP-6, and its detailed restriction map has been prepared. The 4.9-kb plasmid has a G + C content of 57%. It replicates in C. glutamicum ATCC13032 and is compatible with the three other plasmids, pCC1, pBL1 and pHM1519, commonly used for vector construction for amino acid-producing corynebacteria. Fusions of pGA1 with different Escherichia coli replicons (transferred from E. coli to Corynebacterium via transformation of spheroplasts or by filter mating experiments with intact cells) are shown to be suitable as shuttle plasmids; some of them are highly stable in C. glutamicum, even when propagated without any selection pressure.

Cloning vectors and antibiotic-resistance markers for Brevibacterium sp. R312

Replication of several cryptic plasmids from coryneform strains was investigated in Brevibacterium sp. R312. Only the Corynebacterium glutamicum pSR1 replicon was found to be suitable for establishing a host-vector system. Two pSR1 derivatives, pRPCG200 and pHYCG1, were used as cloning vectors. They carry a neomycin-resistance-encoding and a tetracycline-resistance-encoding gene, respectively.

Cloning and expression in Escherichia coli of the homoserine kinase (thrB) gene from Brevibacterium lactofermentum

Five DNA fragments carrying the thrB gene (homoserine kinase E.C. 2.7.1.39) of Brevibacterium lactofermentum were cloned by complementation of Escherichia coli thrB mutants using pBR322 as vector. All the cloned fragments contained a common 3.1 kb DNA sequence. The cloned fragments hybridized among themselves and with a 9 kb BamHI fragment of the chromosomal DNA of B. lactofermentum but not with the DNA of E. coli. None of the cloned fragments were able to complement thrA and thrC mutations of E. coli. Plasmids pULTH2, pULTH8 and pULTH11 had the cloned DNA fragments in the same orientation and were very stable. On the contrary, plasmid pULTH18 was very unstable and showed the DNA inserted in the opposite direction. E. coli minicells transformed with plasmids pULTH8 or pULTH11 (both carrying the common 3.1 kb fragment) synthesize a protein with an Mr of 30,000 that is similar in size to the homoserine kinase of E. coli.

Identification of a promoter sequence in the plasmid pUL340 of Brevibacterium lactofermentum and construction of new cloning vectors for corynebacteria containing two selectable markers

A strong promoter P1 has been found in plasmid pUL340, a cloning vector used to transform corynebacteria. This promoter is also expressed efficiently in Escherichia coli. A gene (cat) for chloramphenicol acetyltransferase from Streptomyces acrimycini and a gene (hyg) for hygromycin phosphotransferase from Streptomyces hygroscopicus were subcloned in different positions of the Brevibacterium lactofermentum plasmid pUL340. Both resistance genes are expressed in B. lactofermentum from their own promoters or from the endogenous promoter in pUL340. These genes provide useful screening markers for selecting transformants of B. lactofermentum together with the kanamycin-resistance gene from the transposon Tn5.

Cloning and expression of tryptophan genes from Brevibacterium lactofermentum in Escherichia coli

A gene bank from the amino acid producer Brevibacterium lactofermentum has been prepared in Escherichia coli using pBR322 as vector. Four clones containing genetic information needed to complement mutations in A,B,C and D genes from E. coli have been isolated. The cloned fragments range between 4.3 kb (pULT61) and 7.9 kb (pULT62). All the four clones contain genetic information that complements trpB gene from E. coli. The cloned trpB gene is very stable and is maintained extrachromosomally in E. coli. It is expressed very efficiently showing high levels of tryptophan synthetase activity.

High-frequency transformation of Brevibacterium lactofermentum protoplasts by plasmid DNA

An efficient polyethylene glycol-assisted method for transformation of Brevibacterium lactofermentum protoplasts that uses plasmid vectors has been developed. Two small plasmids, pUL330 (5.2 kilobases) and pUL340 (5.8 kilobases), both containing the kanamycin resistance gene from transposon Tn5 and the replication origin of the natural plasmid pBL1 of B. lactofermentum, were selected as vectors. Supercoiled forms of the plasmids yielded a 100-fold higher transformation frequency than did linear forms. The optimal transformation frequency was achieved with 10 ng of DNA in 1 ml of transformation buffer. Higher concentrations of plasmid DNA resulted in a decrease in transformation frequency per microgram of DNA. Optimal transformation was obtained with 25 to 35% polyethylene glycol 6000. Under optimal conditions, 10(6) transformants per microgram of DNA were obtained.

Construction of novel shuttle vectors and a cosmid vector for the glutamic acid-producing bacteria Brevibacterium lactofermentum and Corynebacterium glutamicum

Novel cloning vectors for glutamic acid-producing bacteria have been constructed. Two cryptic plasmids, pAM330 from Brevibacterium lactofermentum and pHM1519 from Corynebacterium glutamicum, were used as precursors, and recombined with pBR325 or pUB110. Resultant composite plasmids were able to propagate and to express the CmR or KmR phenotype in B. lactofermentum and C. glutamicum. A smaller, high-copy-number plasmid, pAJ43, was also isolated following deletion of a part of the pAM330-pBR325 composite plasmid. Furthermore, a cosmid vector, which can be packaged and transduced through phage infection, has been developed using a cohesive-end fragment of the f1A phage and plasmid pAJ43. These plasmids are suitable for use as cloning vectors in the glutamic acid-producing bacteria.