Mycelium Differentiation and Antibiotic Production in Submerged Cultures ofStreptomyces coelicolor

Abstract

Despite the fact that most industrial processes for secondary metabolite production are performed with submerged cultures, a reliable developmental model for Streptomyces under these culture conditions is lacking. With the exception of a few species which sporulate under these conditions, it is assumed that no morphological differentiation processes take place. In this work, we describe new developmental features of Streptomyces coelicolor A3(2) grown in liquid cultures and integrate them into a developmental model analogous to the one previously described for surface cultures. Spores germinate as a compartmentalized mycelium (first mycelium). These young compartmentalized hyphae start to form pellets which grow in a radial pattern. Death processes take place in the center of the pellets, followed by growth arrest. A new multinucleated mycelium with sporadic septa (second mycelium) develops inside the pellets and along the periphery, giving rise to a second growth phase. Undecylprodigiosin and actinorhodin antibiotics are produced by this second mycelium but not by the first one. Cell density dictates how the culture will behave in terms of differentiation processes and antibiotic production. When diluted inocula are used, the growth arrest phase, emergence of a second mycelium, and antibiotic production are delayed. Moreover, pellets are less abundant and have larger diameters than in dense cultures. This work is the first to report on the relationship between differentiation processes and secondary metabolite production in submerged Streptomyces cultures.Streptomyces is a soil bacterium that produces numerous clinically useful antibiotics (1, 54, 66), as well as many molecules that affect eukaryotic systems, such as inducers of eukaryotic cellular differentiation, inducers and inhibitors of apoptosis (59), and protein C kinase inhibitors with antitumor activity (such as staurosporine and others) (48, 57). Moreover, its remarkably complex developmental cycle makes this microorganism an interesting subject for study. The traditional developmental cycle of this bacterium describes two differentiated mycelial structures, a substrate (vegetative) mycelium and an aerial (reproductive) mycelium (10,25,33). In the substrate mycelium, septa are thought to be widely spaced and to define compartments containing several nucleoids (10, 63). After a short growth arrest phase characterized by reduced macromolecular synthesis (25), aerial hyphae develop from simple branching from substrate mycelium (29). Finally, the tips of the aerial mycelium differentiate into hydrophobic spore chains (8). Recently, we have been able to extend what is known about the developmental cycle in surface confluent cultures a great deal. Our main contribution has been to reveal the existence of a very young compartmentalized mycelium that dies following an orderly pattern, leaving alternating live and dead segments in the same hypha (37). Subsequently, the remaining live mycelium grows in successive waves that vary according to the density of the ...

Gamma-Butyrolactone Regulatory System of Streptomyces chattanoogensis Links Nutrient Utilization, Metabolism, and Development

“…There are two distinct stages of exponential growth separated by a temporary growth called diauxic lag, which is an adaptive state and reflects depletion of a preferred nutritional source followed by activation of genes required for utilization of alternative substrates (24). Recently, these two stages of exponential growth were found to correspond to two different morphological phases: MI (the first compartmentalized mycelium) and MII (the second multinucleated mycelium) (21,22). These phases were also characterized by distinct protein expression profiles.…”

New Method for Monitoring Programmed Cell Death and Differentiation in Submerged Streptomyces Cultures

“…Although most industrial processes for secondary metabolite production are performed in liquid cultures, Streptomyces strains generally do not sporulate under these conditions (6,18,22), and most authors assumed that differentiation did not take place. Recently, a detailed analysis of Streptomyces differentiation in surface and submerged cultures has been performed, describing novel aspects of the differentiation processes of this bacterium (10)(11)(12)(13)(14)(15)(16)(17). A previously unidentified compartmentalized mycelium (MI) initiates the developmental cycle and then dies following a highly ordered sequence (PCD) (10,11,14).…”

AterDDomain-Encoding Gene (SCO2368) Is Involved in Calcium Homeostasis and Participates in Calcium Regulation of a DosR-Like Regulon in Streptomyces coelicolor

“…As growth kinetics differed within strains ( Fig. 1), the transcriptomes of strain M145 and the ⌬tdd8 strain were compared at the visual onset of Red production, which corresponds to the transition period between the compartmentalized-mycelium (first mycelium) and multinucleated-mycelium (second mycelium) states in a liquid culture (3,4). To ensure that the differences observed in the microarray experiments were not simply due to differences in the growth stages, microarray results were validated for several genes by performing RT-qPCR on cDNA from bacteria of the wild and deletion strains sampled at the onset of Red production (Table 2) and at different time points (Fig.…”

“…This stage is characterized by growth arrest and programmed cell death prior to the appearance of the second mycelium (4). It has been proposed that the growth arrest could be triggered by local oxygen depletion in the developing mycelium (2).…”

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