Construction and application of plasmid- and transposon-based promoter-probe vectors for Streptomyces spp. that employ a Vibrio harveyi luciferase reporter cassette

Structural analysis of the 6 kb cryptic plasmid pFAJ2600 from Rhodococcus erythropolis NI86/21 and construction of Escherichia coli-Rhodococcus shuttle vectors

The complete nucleotide sequence of the 5936 bp cryptic plasmid pFAJ2600 from Rhodococcus erythropolis NI86/21 was determined. Based on the characteristics of its putative replication genes, repA and repB, pFAJ2600 was assigned to the family of pAL5000-related small replicons identified in Mycobacterium (pAL5000), Corynebacterium (pXZ10142), Brevibacterium (pRBL1), Bifidobacterium (pMB1) and Neisseria (pJD1). The replication systems of these plasmids show striking similarities to the ones used by the ColE2 family of plasmids from Enterobacteria with respect to both trans-acting factors and ori sequences. Two possible plasmid stabilization systems are encoded on pFAJ2600: a site-specific recombinase (PmrA) related to the Escherichia coli Xer proteins for plasmid multimer resolution and an ATPase (ParA) related to the A-type of proteins in sop/par partitioning systems. The proposed replication termination region of pFAJ2600 has features in common with the Ter loci of Bacillus subtilis. Chimeras composed of a pUC18-Cmr derivative inserted in the parA-repA intergenic region of vector pFAJ2600 produced vectors that could be shuttled between Escherichia coli and several Rhodococcus species (R. erythropolis, R. fascians, R. rhodochrous, R. ruber). The pFAJ2600-based shuttle vector pFAJ2574 was stably maintained in R. erythropolis and R. fascians growing under non-selective conditions.

Isolation and characterization of a strong promoter element from the Streptomyces ghanaensis phage I19 using the gentamicin resistance gene (aacC1) of Tn 1696 as reporter

A promoter-probe shuttle plasmid (pGL7011) containing the promoterless aminoglycoside-O-acetyltransferase I gene (aacC1) of Tn1696 was used to isolate DNA fragments from Streptomyces ghanaensis phage I19 that possessed promoter activity in Streptomyces lividans TK23. Analysis of gentamicin (Gm) resistance levels in Escherichia coli and in S. lividans TK23, and of aacC1 mRNA levels in S. lividans, identified a fragment (F14) that exhibited a high level of promoter activity in both species. Subsequent analysis revealed that the promoter activity of SF14 (a subcloned fragment of F14) was about twice that of ermEp*, one of the strongest characterized actinomycete promoters. SF14 contained two tandemly arranged promoters, 14-Ip and p14-IIp, with overlapping and adjacent -10 and -35 regions, respectively. Both promoters appear to be recognized with different efficiencies by the major RNA polymerase holoenzyme (E sigma hrdB) of Streptomyces coelicolor A3(2).

Construction and symbiotic competence of a luxA-deletion mutant of Vibrio fischeri

Bioluminescence by the squid Euprymna scolopes requires colonization of its light organ by the symbiotic luminous bacterium Vibrio fischeri. Investigation of the genetic determinants underlying bacterial symbiotic competence in this system has necessitated the continuing establishment and application of molecular genetic techniques in V. fischeri. We developed a procedure for the introduction of plasmid DNA into V. fischeri by electroporation, and isolated a mutant strain that overcame the apparent restriction barrier between V. fischeri and Escherichia coli. Using the technique of electroporation in combination with that of gene replacement, we constructed a non-luminous strain of V. fischeri (delta luxA::erm). In addition, we used the transducing phage rp-1 for the first time to transfer a chromosomal antibiotic resistance marker to another strain of V. fischeri. The luxA mutant was able to colonize E. scolopes as quickly and to the same extent as wild type. This result suggested that, at least during the initial stages of colonization, luminescence per se is not an essential factor for the symbiotic infection.

The sapA promoter from Streptomyces coelicolor requires activation sites and initiator-like sequences but No -10 or -35 sequences

The Streptomyces coelicolor sapA gene encodes a spore coat protein. The sapA promoter is regulated developmentally, with maximal expression occurring in aerial hyphae at a late stage of colonial development. The DNA sequences upstream from the transcription start point do not appear to fall into a previously described promoter class. One (or more) putative activation site, required for full activity, is eliminated when 5' deletions extend to between -178 and -72 bases upstream from the transcription start point. In addition, a downstream activation site is destroyed by removing sequences between positions +40 and +120, relative to the transcription start point, in the absence of an intact upstream region. However, temporal regulation of transcription initiation over the course of the life cycle is maintained faithfully in the absence of these elements, even in the smallest 18-bp sapAp fragment containing sequences from positions -8 to +10. Site-specific mutations around the transcriptional start points shift the timing of sapA expression to an earlier stage in the developmental cycle. These results sugges that a novel mechanism may be involved in Streptomyces late gene expression.

Tn4556 and luciferase: synergistic tools for visualizing transcription in Streptomyces

Progress in understanding genetic regulatory controls in the Actinomycetes has been rate limited by the properties of in vivo transcriptional probes. We have developed a set of plasmid- and transposon-based promoter-probe vectors that employ the Vibrio harveyi luciferase-encoding luxAB cassette as a reporter of transcription. The primary advantages of luciferase (Lux) over other reporter gene products are: (i) unsurpassed sensitivity; (ii) utility during stationary-phase gene expression; and (iii) the ability to localize promoter activity spatially within developing colonies. We have used these vectors to screen for Streptomyces coelicolor promoters that exhibit developmental phenotypes or that are induced by various environmental stimuli. The plasmid-based probes have proved invaluable for identifying cis- and trans-acting elements that are required for stationary-phase expression of the S. coelicolor sapA gene. A collection of novel bld and whi insertion mutants has been obtained by use of the Lux-encoding transposon, Tn5353.