Browsing by Author "Jayathilake, K. M. P. I."

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Biovalorization of agro-food wastes for the production of melanin pigment via a submerged fermentation process using Aspergillus niger: as a sustainable approach
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Rasna, N. F.; Jayathilake, K. M. P. I.; Manage, P. M.; Idroos, F. S.
Biovalorization harnesses biological processes to convert waste materials into value added products, encouraging sustainability and resource efficiency. The current study aims to explore and optimize a sustainable method for the production of melanin pigment through the submerged fermentation (SMF) process by utilizing banana peel waste, affected Sesbania grandiflora leaves and stem wastes, and used tea dust waste using Aspergillus niger. The pH, moisture content, total organic carbon, and total ash contents of collected food wastes were measured using standard methods. Fungal cultures were incubated under the submerged fermentation process, at 25 °C with an agitation speed of 160 rpm for 14 days. Subsequently, the fungal-produced pigment was extracted using 1.0 mol/L KOH and subsequently characterized using physicochemical tests with water, organic solvents, alkaline and acidic solutions, and an oxidizing-reducing agent. Further, the pigment was confirmed based on ultraviolet-visible spectroscopic analysis and Fourier-transform infrared spectroscopic (FTIR) analysis. The extracted pigment was tested for toxicity, antibacterial, and antioxidant properties to the determination of the distinctive characteristics and quality of the extracted pigment, hence enabling their industrial use. The pigment yield from banana, Sesbania, and tea wastes were 597.2 ± 21.5 mg/L, 395.4 ± 39.1 mg/L, and 135 ± 12.9 mg/L, respectively. Compared to the control setup, a significant difference (p < 0.05) was observed between the pigment yields produced by A. niger when utilizing different types of food waste. In the physico-chemical analysis, the blackish brown colour of the pigment served as primary evidence for melanin. The pigment was insoluble in water and organic solvents (acetone, chloroform, ethanol, and sodium acetate), but it was readily soluble in KOH and NaOH, precipitated with HCl, and decolorized with H₂O₂. The UV-Vis spectrum indicated that the pigment possessed a λmax around 213–216 nm. The FTIR spectrum showed broad bands around 3000– 3500 cm⁻¹ (OH), 2924.7 and 1032.6 cm⁻¹ (saturated carbon and C-O), 2830–2930 cm⁻¹ (CH2 and CH3), 1500–1650 cm⁻¹ (aromatic C=C or C=O), 1320 and 1390 cm⁻¹ (C-N), and 1210–1230 cm⁻¹ (C-OH). The extracted pigment exhibited low toxicity to mung beans (4.4–6.7%) compared to the positive control (100% extraction solvent). In the antibacterial activity assay, inhibition zones ranged from 2.1 ± 0.1 to 2.6 ± 0.1 cm for Staphylococcus aureus and 2.1 ± 0.1 to 2.5 ± 0.1 cm for Escherichia coli. The antioxidant assay demonstrated an increase in the percentage of DPPH inhibition with increasing pigment concentration, suggesting the pigment's ability to scavenge free radicals. This study proposes a sustainable approach for the production of fungal-based pigment (melanin) through a submerged fermentation process utilizing agro-food wastes with Aspergillus niger strain, which was not documented in previous studies.
Isolation and characterization of nitrogen-fixing bacteria from compost soil and their impact on nitrogen uptake and plant growth
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Jayathilake, K. M. P. I.; Manage, P. M.; Idroos, F. S.
Nitrogen-fixing bacteria play a critical role in sustainable agriculture by enhancing soil nitrogen availability, reducing the need for synthetic fertilizers, and promoting plant growth. This study aimed to isolate and characterize nitrogen-fixing bacterial (NFB) strains from compost soil and evaluate their potential to improve nitrogen uptake and plant growth. NFB strains were isolated from compost soil in Karadiyana (6°48′ 51.8′′ N, 79° 54′ 17.0′′ E) using an Ashby medium. The molecular level identification of each isolate was carried out using the 16S rRNA gene region. The production ability of ammonia, nitrate, and nitrite was determined after 7 days of incubation in Ashby broth medium inoculated with each isolated strain. The effect of isolated NFB strains on plant growth was determined using a pot experiment. The isolated nitrogen-fixing bacteria (NFB) strains were introduced to the developed potting media prepared with compost, coir dust, and soil in a 1:1:1 ratio, with mung bean (Vigna radiata) selected as the experimental plant. Control potting media was prepared without the inoculation of NFB strains. Shoot length, root length, wet weight, and dry weight of the grown plants were measured after 30 days of the seed germination period as growth parameters to determine the effect of the isolated NFB strains. The molecular level identification confirmed that the isolated strains were Microbacterium aquimaris (CTD16), Bacillus xiamenensis (MCCC 1A00008), Bacillus aerophilus (XA5-12), Bacillus subtilis (NCIB 3610), Bacillus cereus (CCM 2010), Bacillus subtilis (BHU7), and Bacillus aerius (24K). The highest ammonia (1.6 ± 0.5 mg/L) and nitrate (1.08 ± 0.04 mg/L) production were recorded in Ashby broth media inoculated with B. cereus after 7 days of incubation. Pots inoculated with NFB strains showed a significant increase in measured growth parameters compared to the control (n = 9, p < 0.05). Potting media inoculated with B. cereus strain CCM 2010 showed the best results, with the highest root length (11.3 ± 1.1 cm) and shoot length (17.5 ± 0.5 cm), wet weight (0.6898 ± 0.1 g), and dry weight (0.1015 ± 0.01 g) recorded. The study demonstrated that all isolated Bacillus spp. and Microbacterium aquimaris exhibited significant roles in nitrogen fixation. These findings indicate their potential as effective biofertilizers, contributing to enhanced nitrogen availability and improved plant health.
Isolation, characterization, and application of phosphate-solubilizing fungi as a biofertilizer for plant growth promotion
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Jayathilake, K. M. P. I.; Manage, P. M.; Idroos, F. S.
Plants require major nutrients such as nitrogen and phosphorus for their optimal growth. Phosphorus is an essential macronutrient, yet its availability in soil is often limited due to its insoluble form. Soil microbes can convert insoluble phosphate into soluble phosphate through various mechanisms. Phosphate-solubilizing fungi (PSF) play a vital role in this process, contributing to the phosphorus requirements of plants. Hence, the present study aimed to isolate, characterize, and utilize PSF as a biofertilizer. The PSF strains were isolated from compost soil in Karadiyana (6°48′ 51.8′′ N, 79° 54′ 17.0′′ E) using Pikovskaya's agar (PVK) medium. The phosphate solubilizing index (PSI) was determined by observing halo zone formation after a 7-day incubation period. Phosphate solubilizing efficiency was assessed using PVK broth supplemented with 0.5% tricalcium phosphate following 7 days of incubation at 160 rpm (28 oC). The isolated fungal strains were introduced to a developed potting medium containing compost, coir dust, and soil in a 1:1:1 ratio. Mung bean (Vigna radiata) was selected as the experimental plant. Plant growth parameters (shoot length, root length, wet weight, and dry weight) were measured to determine the effect of the isolated fungal strains. These parameters were recorded after 30 days. Genotypic identification of the isolated strains was performed using the Internal Transcribed Spacer (ITS) region. The strains were confirmed as Fusarium proliferatum, Aspergillus niger, and Aspergillus flavus. A. niger demonstrated the highest phosphate solubilizing efficiency (296.8 ± 0.2 μg/mL) after 6 days of incubation, with a PSI of 2.15 ± 0.1. Fungi-inoculated pots showed a significant increase in shoot length, root length, wet weight, and dry weight compared to the control (n = 9, p < 0.05). Potting media inoculated with A. niger showed the best results, with the highest root length (11.8 ± 0.5 cm), shoot length (16.7 ± 0.5 cm), wet weight (0.6381 ± 0.03 g), and dry weight (0.1060 ± 0.02 g) was recorded. This study suggests that the potting media containing F. proliferatum, A. niger, and A. flavus exhibited significant roles in phosphate solubilization and plant growth promotion, indicating their potential to be used as an effective biofertilizers.