Microbe Profile: Salinispora tropica: natural products and the evolution of a unique marine bacterium.

Salinispora tropica was originally cultured from tropical marine sediments and described as the first obligate marine actinomycete genus. Soon after its discovery, it yielded the potent proteasome inhibitor salinosporamide A, a structurally novel natural product that is currently in phase III clinical trials for the treatment of cancer. If approved, it will be the first natural product derived from a cultured marine microbe to achieve clinical relevance. S. tropica produces many other biologically active natural products, including some linked to chemical defence, thus providing ecological context for their production. However, genomic analyses reveal that most natural product biosynthetic gene clusters remain orphan, suggesting that more compounds await discovery. The abundance of biosynthetic gene clusters in S. tropica supports the concept that the small molecules they encode serve important ecological functions, while their evolutionary histories suggest a potential role in promoting diversification. Better insights into the ecological functions of microbial natural products will help inform future discovery efforts.

Laboratory scale cultivation of Salinispora tropica in shake flasks and mechanically stirred bioreactors.

OBJECTIVE: Marine actinomycetes from the genus Salinispora have an unexploited biotechnological potential. To accurately estimate their application potential however, data on their cultivation, including biomass growth kinetics, are needed but only incomplete information is currently available. RESULTS: This work provides some insight into the effect of temperature, salinity, nitrogen source, glucose concentration and oxygen supply on growth rate, biomass productivity and yield of Salinispora tropica CBN-440T. The experiments were carried out in unbaffled shake flasks and agitated laboratory-scale bioreactors. The results show that the optimum growth temperature lies within the range 28-30 °C, salinity is close to sea water and the initial glucose concentration is around 10 g/L. Among tested nitrogen sources, yeast extract and soy peptone proved to be the most suitable. The change from unbaffled to baffled flasks increased the volumetric oxygen transfer coefficient (kLa) as did the use of agitated bioreactors. The highest specific growth rate (0.0986 h-1) and biomass productivity (1.11 g/L/day) were obtained at kLa = 28.3 h-1. A further increase in kLa was achieved by increasing stirrer speed, but this led to a deterioration in kinetic parameters. CONCLUSIONS: Improvement of S. tropica biomass growth kinetics of was achieved mainly by identifying the most suitable nitrogen sources and optimizing kLa in baffled flasks and agitated bioreactors.

Influence of Cultivation Conditions on the Sioxanthin Content and Antioxidative Protection Effect of a Crude Extract from the Vegetative Mycelium of Salinispora tropica.

Due to their bioavailability, glycosylated carotenoids may have interesting biological effects. Sioxanthin, as a representative of this type of carotenoid, has been identified in marine actinomycetes of the genus Salinispora. This study evaluates, for the first time, the effect of cultivation temperature (T) and light intensity (LI) on the total cellular carotenoid content (TC), antioxidant activity (AA) and sioxanthin content (SX) of a crude extract (CE) from Salinispora tropica biomass in its vegetative state. Treatment-related differences in TC and SX values were statistically significantly and positively affected by T and LI, while AA was most significantly affected by T. In the S. tropica CE, TC correlated well (R2 = 0.823) with SX and somewhat less with AA (R2 = 0.777). A correlation between AA and SX was found to be less significant (R2 = 0.731). The most significant protective effect against oxidative stress was identified in the CE extracted from S. tropica biomass grown at the highest T and LI (CE-C), as was demonstrated using LNCaP and KYSE-30 human cell lines. The CE showed no cytotoxicity against LNCaP and KYSE-30 cell lines.

Genome-scale reconstruction of Salinispora tropica CNB-440 metabolism to study strain-specific adaptation.

The first manually curated genome-scale metabolic model for Salinispora tropica strain CNB-440 was constructed. The reconstruction enables characterization of the metabolic capabilities for understanding and modeling the cellular physiology of this actinobacterium. The iCC908 model was based on physiological and biochemical information of primary and specialised metabolism pathways. The reconstructed stoichiometric matrix consists of 1169 biochemical conversions, 204 transport reactions and 1317 metabolites. A total of 908 structural open reading frames (ORFs) were included in the reconstructed network. The number of gene functions included in the reconstructed network corresponds to 20% of all characterized ORFs in the S. tropica genome. The genome-scale metabolic model was used to study strain-specific capabilities in defined minimal media. iCC908 was used to analyze growth capabilities in 41 different minimal growth-supporting environments. These nutrient sources were evaluated experimentally to assess the accuracy of in silico growth simulations. The model predicted no auxotrophies for essential amino acids, which was corroborated experimentally. The strain is able to use 21 different carbon sources, 8 nitrogen sources and 4 sulfur sources from the nutrient sources tested. Experimental observation suggests that the cells may be able to store sulfur. False predictions provided opportunities to gain new insights into the physiology of this species, and to gap fill the missing knowledge. The incorporation of modifications led to increased accuracy in predicting the outcome of growth/no growth experiments from 76 to 93%. iCC908 can thus be used to define the metabolic capabilities of S. tropica and guide and enhance the production of specialised metabolites.

Bioactive natural products from the genus Salinospora: a review.

Actinomycetes are an important source for bioactive secondary metabolites. Among them, the genus Salinispora is one of the first salt obligatory marine species worldwide and is typically found in various types of substrates in tropical and subtropical marine environments including sediments and marine organisms. This genus produces a wide range of chemical scaffolds and bioactive compounds such as lomaiviticins, cyclomarins, rifamycins, salinaphthoquinones, and salinosporamides. This review arranged Salinispora derived secondary metabolites according to the three species that comprise the genus. Moreover, muta- and semi-synthesis analogs derived from salinosporamide were also described in this review.

Biological activity of sporolides A and B from Salinispora tropica: in silico target prediction using ligand-based pharmacophore mapping and in vitro activity validation on HIV-1 reverse transcriptase.

Sporolides A and B are novel polycyclic macrolides from the obligate marine actinomycetes, Salinispora tropica. The unique and novel structure of sporolides makes them interesting candidates for targeting diverse biological activities. Biological target prediction of sporolides was carried out using ligand-based pharmacophore screening against known inhibitors and drugs. Validation of pharmacophore screening was carried out for the identified hits. New biological targets predicted for sporolides using this method were HIV-1 reverse transcriptase, adenosine A3 receptor, endothelin receptor ET-A, oxytocin receptor, voltage-gated L-type calcium channel α-1C subunit/calcium channel α/Δ subunit 1. Drug-likeness properties were predicted for the selected compounds using QikProp module. Sporolides A and B showed maximum docking score with HIV-1 reverse transcriptase. Structural interaction fingerprints analysis indicated similar binding pattern of the sporolides with the HIV-1 reverse transcriptase. Sporolide B exhibited good inhibitory activity against HIV-1 reverse transcriptase in in vitro fluorescent assay.