RESEARCH SUMMARY

The group has traditionally focused its research on the physiological and molecular characterisation of the main protein secretion mechanism (Sec system) of the soil Gram-positive bacteria of the Streptomyces genus, namely S. lividans and S. coelicolor. These are widely used in industry as efficient producers of extracellular hydrolytic enzymes and other compounds of industrial interest.

Deficiency in the translocase complex (SecG mutant strain) or the major type I signal peptidase (SipY mutant strain) function in S. lividans results in a group of genes seemingly regulated in the same way when the translocation process of extracellular proteins is restricted, or when extracellular protein processing is compromised, including the absence of secretory protein production in both cases and a sporulation deficient bald phenotype. Transcriptional profiling and proteomic analyses of both S. lividans strains revealed a set of equally regulated bld-related genes. A bald phenotype is acquired in both mutant strains by downregulation of bld chain genes. Although a common regulator has not yet been identified, most of the commonly regulated genes can be linked directly or indirectly to the bld cascade, strongly suggesting its involvement in the cell response to the secretory defect of both mutant strains.

A S. coelicolor two-gene operon encodes a two-component system: a histidine-kinase sensor and a response regulator protein. Propagation of the regulatory gene in high copy number results in overproduction of several extracellular proteins, as well as eliciting a partial stringent response and an altered pattern of antibiotic synthesis in the bacterial cell, as determined by proteomic and transcriptomic analyses. This two-component system is currently under study in S. coelicolor, as it seems to influence various processes characterised by the transition from primary to secondary metabolism.

The laboratory has started a new research line focused on molecular monitoring of the rhizobial communities of transgenic plants. Rhizobacterial communities of transgenic maize engineered to express the Bacillus thuringensis Cry toxin (Bt maize) have been monitored for a number of years in three agricultural soils, using commercially available DNA microarrays containing genome-wide spotted oligonucleotides that encompass the soil bacteria B. subtilis and S. coelicolor. The results showed that genome-wide DNA arrays could be a useful tool for molecular monitoring of rhizobacterial communities to assess potential environmental risk associated with cultivation of transgenic plants.

We compared the effect of glyphosate (RoundupPlus), a post-emergency applied herbicide, and HarnessGTZ, a pre-emergency applied herbicide, on the rhizobacterial communities of genetically modified NK603 glyphosate-tolerant maize. The potential effect was monitored by direct amplification, cloning and sequencing of soil DNA encoding 16S rRNA, rhizobacterial DNA hybridisation to commercially available genome-wide microarrays from the soil bacterium S. coelicolor, and high throughput DNA pyrosequencing of the bacterial DNA coding for the 16S rRNA hypervariable V6 region. The results strongly suggest that both herbicides do affect the maize rhizobacterial communities, with glyphosate being, to a great extent, the environmentally less aggressive herbicide.