Unlocking a new target for streptomycetes strain improvement

Metabolite profiling of endophytic Streptomyces spp. and its antiplasmodial potential

Background

Antiplasmodial drug discovery is significant especially from natural sources such as plant bacteria. This research aimed to determine antiplasmodial metabolites of Streptomyces spp. against Plasmodium falciparum 3D7 by using a metabolomics approach.

Methods

Streptomyces strains' growth curves, namely SUK 12 and SUK 48, were measured and P. falciparum 3D7 IC₅₀ values were calculated. Metabolomics analysis was conducted on both strains' mid-exponential and stationary phase extracts.

Results

The most successful antiplasmodial activity of SUK 12 and SUK 48 extracts shown to be at the stationary phase with IC₅₀ values of 0.8168 ng/mL and 0.1963 ng/mL, respectively. In contrast, the IC₅₀ value of chloroquine diphosphate (CQ) for antiplasmodial activity was 0.2812 ng/mL. The univariate analysis revealed that 854 metabolites and 14, 44 and three metabolites showed significant differences in terms of strain, fermentation phase, and their interactions. Orthogonal partial least square-discriminant analysis and S-loading plot putatively identified pavettine, aurantioclavine, and 4-butyldiphenylmethane as significant outliers from the stationary phase of SUK 48. For potential isolation, metabolomics approach may be used as a preliminary approach to rapidly track and identify the presence of antimalarial metabolites before any isolation and purification can be done.

The Inhibition of Antibiotic Production in Streptomyces coelicolor Over-Expressing the TetR Regulator SCO3201 IS Correlated With Changes in the Lipidome of the Strain

In condition of over-expression, SCO3201, a regulator of the TetR family was previously shown to strongly inhibit antibiotic production and morphological differentiation in Streptomyces coelicolor M145. In order to elucidate the molecular processes underlying this interesting, but poorly understood phenomenon, a comparative analysis of the lipidomes and transcriptomes of the strain over-expressing sco3201 and of the control strain containing the empty plasmid, was carried out. This study revealed that the strain over-expressing sco3201 had a higher triacylglycerol content and a lower phospholipids content than the control strain. This was correlated with up- and down- regulation of some genes involved in fatty acids biosynthesis (fab) and degradation (fad) respectively, indicating a direct or indirect control of the expression of these genes by SCO3201. In some instances, indirect control might involve TetR regulators, whose encoding genes present in close vicinity of genes involved in lipid metabolism, were shown to be differentially expressed in the two strains. Direct interaction of purified His6-SCO3201 with the promoter regions of four of such TetR regulators encoding genes (sco0116, sco0430, sco4167, and sco6792) was demonstrated. Furthermore, fasR (sco2386), encoding the activator of the main fatty acid biosynthetic operon, sco2386-sco2390, has been shown to be an illegitimate positive regulatory target of SCO3201. Altogether our data demonstrated that the sco3201 over-expressing strain accumulates TAG and suggested that degradation of fatty acids was reduced in this strain. This is expected to result into a reduced acetyl-CoA availability that would impair antibiotic biosynthesis either directly or indirectly.

Negative Correlation between Lipid Content and Antibiotic Activity in Streptomyces: General Rule and Exceptions

Streptomycetes are well known antibiotic producers and are among the rare prokaryotes able to store carbon as lipids. Previous comparative studies of the weak antibiotic producer Streptomyces lividans with its ppk mutant and with Streptomyces coelicolor, which both produce antibiotics, suggested the existence of a negative correlation between total lipid content and the ability to produce antibiotics. To determine whether such a negative correlation can be generalized to other Streptomyces species, fifty-four strains were picked randomly and grown on modified R2YE medium, limited in phosphate, with glucose or glycerol as the main carbon source. The total lipid content and antibiotic activity against Micrococcus luteus were assessed for each strain. This study revealed that the ability to accumulate lipids was not evenly distributed among strains and that glycerol was more lipogenic than glucose and had a negative impact on antibiotic biosynthesis. Furthermore, a statistically significant negative Pearson correlation between lipid content and antibiotic activity could be established for most strains, but a few strains escape this general law. These exceptions are likely due to limits and biases linked to the type of test used to determine antibiotic activity, which relies exclusively on Micrococcus luteus sensitivity. They are characterized either by high lipid content and high antibiotic activity or by low lipid content and undetectable antibiotic activity against Micrococcus luteus. Lastly, the comparative genomic analysis of two strains with contrasting lipid content, and both named Streptomyces antibioticus (DSM 41,481 and DSM 40,868, which we found to be phylogenetically related to Streptomyces lavenduligriseus), indicated that some genetic differences in various pathways related to the generation/consumption of acetylCoA could be responsible for such a difference.