MSc

The study entitled “Green synthesised silver nanoparticles for suppression of algal growth” was carried out during 2016-2019, in the Department of Plant Biotechnology, College of Agriculture, Vellayani. The objective of the study was to green synthesise silver nanoparticles using leaf extracts of plants having antialgal property and to evaluate their potential for the growth inhibition of model alga Chlamydomonas sp.
In the present study, green synthesis of silver nanoparticles was carried out using leaf extracts of giloy (Tinospora cordifolia), castor (Ricinus communis) and water hyacinth (Eichhornia crassipes). The peak of the UV- visible spectra of the silver nitrate solution after treating with the leaf extracts (10% v/v) ranged from 360-460 nm indicating green synthesis of silver nanoparticles by biological reduction.
Growth kinetics of Chlamydomonas reinhardtii (C. reinhardtii) was carried out in Bold’s Basal Medium (BBM) based on functional relationship between time and population for determining the exponential growth phase of C. reinhardtii for further treatment with green synthesised silver nanoparticles. The exponential phase of growth was found to be from eighth to twelfth day of inoculation, with maximum growth on the twelfth day.
Antialgal property of the green synthesised silver nanoparticles was determined by agar well diffusion inhibition, disc diffusion and spot-on lawn assays. Green synthesised silver nanoparticles (5 ppm) prepared using Tinospora cordifolia (T. cordifolia) leaf extract exhibited maximum inhibition of growth on C. reinhardtii followed by silver nanoparticles prepared using Ricinus communis and Eichhornia crassipes in all the three assays. Chemically synthesised silver nanoparticles of 100 nm size (Sigma Aldrich USA) did not exhibit inhibition of growth on C. reinhardtii.
C. reinhardtii cultures were treated separately on the day of inoculation and at the beginning of the exponential growth phase using green synthesised silver nanoparticles of T. cordifolia and population assays were carried out to reconfirm the antialgal property. When green synthesised silver nanoparticles were added on the same day of inoculation of C. reinhardtii, the population count on logarithmic basis (1.01 log cfu ml-1) showed a reduction on the twelfth day compared to the untreated control (5.94 log cfu ml-1). When green synthesised silver nanoparticles were added at the beginning of the exponential phase of growth of C. reinhardtii, the population count (1.84 log cfu ml-1) showed a reduction on the eighth day compared to the untreated control (6.11 log cfu ml-1). This study showed that green synthesised silver nanoparticles from T. cordifolia were able to inhibit the growth of C. reinhardtii at different stages of growth of the algae, demonstrating its antialgal property.
Variations in biochemical parameters viz., total chlorophyll, carbohydrate, protein and lipid contents were recorded at three days interval, after treating the culture solution of C. reinhardtii at the exponential growth phase (Day 12) with green synthesized silver nanoparticles of T. cordifolia. The carbohydrate content (2.46 µg ml-1) showed a significant reduction in the treated cultures but it increased in the untreated control (16.84 µg ml-1) on the eighth day of inoculation. Protein content (6.27 µg ml-1) also significantly reduced in the treated culture compared to untreated control (25.93 µg ml-1) on eighth day of inoculation. The chlorophyll content (5.96 µg ml-1) remained stable on the eighth day in the treated culture whereas in the untreated control, approximately 2.5 times increase was recorded (15.21 µg ml-1). Lipid content in treated and untreated culture solution was below detectable levels.
Results of the present study indicated that green synthesised silver nanoparticles using leaf extract of T. cordifolia was able to inhibit the growth of C. reinhardtii, thus exhibiting potential antialgal property. The study can be further extended to harmful algae for developing an ecofriendly approach for their control using green synthesised silver nanoparticles