In vitro antiparasitic activity of microbial pigments and their combination with phytosynthesized metal nanoparticles.

Bioactive pigments were extracted and purified from cultures of Serratia marcescens and Chromobacterium violaceum. Spectroscopic, FTIR, and HPLC analyses showed prodigiosin and violacein as the principle molecules in the extract. Bioactive microbial pigments prodigiosin, violacein and their combinations with phytosynthesized silver and gold nanoparticles were studied for in vitro growth inhibition of Plasmodium falciparum and Trypanosoma brucei gambiense. Prodigiosin was found to be more effective than violacein for inhibition of both parasites in vitro. Specifically, combinations of the microbial pigment prodigiosin with metal nanoparticles showed a significant decrease in the IC50 values on both parasites (2.7 to 3.6 fold) without increase of cytotoxicity upon mammalian cells. The data may be useful for the microbial pigment based drug designing.

Maintenance of residual activity of Bt toxin by using natural and synthetic dyes: a novel approach for sustainable mosquito vector control.

Mosquito control protein from Bacillus thuringiensis gets inactivated with exposure to sunlight. To address this issue, the potential of synthetic and natural dye was investigated as sunlight protectants. Bt SV2 in absence of dyes when exposed to sunlight showed reduced effectiveness against the fourth instars of mosquito larvae. Whereas acriflavin, congo red and violacein were able to maintain 86.4%, 91.6% and 82.2% mosquito larvicidal efficacy of Bt SV2 against IVth instars larvae of Anopheles stephensi Meigen after exposure to sunlight. Similarly, beetroot dye, acriflavin, congo red and violacein maintained 98.4%, 97.1%, 90.8% and 70.7% larvicidal activities against Aedes aegypti Linnaeus after sunlight exposure. Prodigiosin was found to be the best photo-protectant by simultaneously protecting and enhancing Bt activity by 6.16% and 22.16% against A. stephensi and A. aegypti, respectively. Combination of dyes with Bt formulations can be a good strategy for mosquito control programmes in tropical and sub-tropical regions.

Nematicidal activity of microbial pigment from Serratia marcescens.

Ineffectiveness of available nematicides and the high damage caused by plant-parasitic nematodes result in the urgent need to find some natural remedy for their control. Bioactivity of the pigment extracted from Serratia marcescens was screened for controlling nematodes at their juvenile stage. Test pigment was found effective against juvenile stages of Radopholus similis and Meloidogyne javanica at low concentrations (LC50 values, 83 and 79 µg/mL, respectively) as compared with positive control of copper sulphate (LC50 values, 380 and 280 µg/mL, respectively). The pigment also exhibited inhibition on nematode egg-hatching ability. Characterisation of extracted pigment with TLC, FTIR, HPLC, HPTLC and spectroscopic analysis confirmed the presence of prodigiosin as a bioactive metabolite. Considering the sensory mechanism of pathogen recognition by nematodes, the use of microbial secondary metabolites can be effective for nematode control rather than using whole organism.