STALIQS · Characterization of differentiation, anaerobiosis, and stress response in standing liquid cultures of Streptomyces coelicolor by a functional genomics approach

Final Activity Report Summary - STALIQS (Characterization of differentiation, anaerobiosis ... in standing liquid cultures of Streptomyces coelicolor by a functional genomics approach)

Streptomycetes are important to our welfare because they form the source of the majority of natural antibiotics used to cure infectious diseases and provide us with numerous other therapeutics used, for example, to treat cancer. Streptomycetes live in soil and often encounter harsh conditions, such as shortage of oxygen; however we know little about how they survive these conditions. Until recently, it was thought that streptomycetes were unable to grow without oxygen. We demonstrated though that streptomycetes could grow in an oxygen-deficient environment in standing liquid broth. The mode of growth changed to fermentation, which was a type of anaerobic metabolism. Disruption of some fermentation genes prevented the formation of fermentation products, but did not abolish growth or affect anaerobic survival. Furthermore, these bacteria found a way to escape the oxygen shortage by forming colonies that moved to the air and liquid boundary, which contained sufficient oxygen for good growth. It was expected that gas vesicles provided streptomyces the observed buoyancy. Gas vesicles were gas-filled prokaryotic organelles that acted as flotation devices, enabling planktonic cyanobacteria and halophilic archaea to position themselves within the water column to make optimal use of light and nutrients. Few terrestrial microbes were known to encode gas vesicle genes. Genome sequences that recently became available for many bacteria from non-planktonic habitats revealed gas vesicle gene clusters in the actinomycete genera streptomyces, frankia, and rhodococcus sp. which typically lived in soils and sediments. There was an additional level of complexity in cluster number and gene product content. The c-terminus of the major gas vesicle protein GvpA was highly unusual because it contained high levels of glutamate and arginine, often present in long, alternating acidic and basic tracts, as mentioned by G. van Keulen et al. in ‘Trends in Microbiology’ in 2005. The amino acid sequences and domains of the actinomycete-specific gas vesicle proteins GvpY and GvpZ were also extraordinary. GvpY had an extremely acidic core with a highly basic c-terminal region. The core of GvpZ resembled a polyketide cyclise and dehydratase domain, which was followed by an acidic c-terminus containing high levels of glutamate (refer to G. van Keulen, ‘Microbiology Monographs’, 2006). My work showed that gas vesicle genes, although expressed at low levels in standing liquid cultures, were not required for the flotation of s. Coelicolor, implicating that gas vesicles fulfilled a different function in actinomycetes. Mutant studies showed that gas vesicle genes might be involved in (osmo)stress adaptation.

Data: CORDIS, © European Union