Thraustochytrids are the most promising microbial source for the commercial production of docosahexaenoic acid (DHA) for its application in the human health, aquaculture, and nutraceutical sectors. The present study isolated 127 thraustochytrid strains from mangrove habitats of the south Andaman Islands, India to study their diversity, polyunsaturated fatty acids (PUFAs), and biotechnological potential. The predominant strains were identified as belonging to two major genera (Thraustochytrium, Aurantiochytrium) based on morphological and molecular characteristics. The strain ANVKK-06 produced the maximum biomass of 5.42 g·L⁻¹, while ANVKK-03 exhibited the maximum total lipid (71.03%). Omega-3 PUFAs such as eicosapentaenoic acid (EPA) accumulated up to 11.03% in ANVKK-04, docosapentaenoic acid (DPA) up to 8.65% in ANVKK-07, and DHA up to 47.19% in ANVKK-06. ANVKK-06 showed the maximum scavenging activity (84.79 ± 2.30%) while ANVKK-03 and ANVKK-10 displayed the highest antibacterial activity against human and fish pathogens, S. aureus (18.69 ± 1.2 mm) and V. parahaemolyticus (18.31 ± 1.0 mm), respectively. All strains were non-toxic as evident by negative blood agar hemolysis, thus, the thraustochytrids are suggested to be a potential source of DHA for application in the health care of human and fish.

Thraustochytrids contribute to the microbiota of mangrove ecosystem, and they hold promise as a potential source of polyunsaturated fatty acids (PUFAs), antimicrobials and antioxidants for their application in pharmaceutical, aquaculture, and human health sectors. However, the thraustochytrids have not been properly studied in Indian mangrove ecosystems for their PUFAs and biological activities, and hence, the present study was carried to isolate the PUFAs-rich thraustochytrids for their pigments, antimicrobial and antioxidant properties. This work isolated and identified the thraustochytrids that are capable of producing PUFAs from decomposing leaves of mangroves at Pichavaram, southeast coast of India. Two predominant isolates were identified as Thraustochytrium sp. and Aurantiochytrium mangrovei based on morphological and molecular characteristics. Thraustochytrium sp., produced the biomass of 4.72 g L^-1, containing total lipids of 42.36% and docosahexaenoic acid (DHA) of 32.69% of total lipids, whereas, A. mangrovei produced the biomass of 6.25 g L^-1 containing total lipids of 49.81% and DHA of 44.71% of total lipids. Astaxanthin pigment accumulated up to 3.2 µg L^-1 in A. mangrovei, whereas the pigment was not detected in Thraustochytrium sp. Further, the biomass extracted in organic solvents was tested for antibacterial activity against seven clinical pathogens along with positive control of ampicillin. Thraustochytrium sp., exhibited the highest antibacterial activity with the zone of inhibition of 78.77% against Staphylococcus aureus and the lowest (20.95%) against Klebsiella pneumonia. Thraustochytrium sp., also showed minimum inhibitory concentration (MIC) of 40 µg L^-1 inhibiting the growth of S. aureus. The antioxidant activity of A. mangrovei was tested by using six assays and noted the highest free radical scavenging (87.37 ± 1.22%) and the lowest nitric oxide radical scavenging (75.12 ± 2.22%) activities. Hence, it is clear that the extracts of Thraustochytrium sp., and A. mangrovei are promising sources of lead compounds for biopharma and food industries.

This work deals with the identification of a predominant thraustochytrid strain, the optimization of culture conditions, the synthesis of nanoparticles, and the evaluation of antioxidant and antimicrobial activities in biomass extracts and nanoparticles. Thraustochytrium kinnei was identified as a predominant strain from decomposing mangrove leaves, and its culture conditions were optimized for maximum biomass production of 13.53 g·L⁻¹, with total lipids of 41.33% and DHA of 39.16% of total fatty acids. Furthermore, the strain was shown to synthesize gold and silver nanoparticles in the size ranges of 10–85 nm and 5–90 nm, respectively. Silver nanoparticles exhibited higher total antioxidant and DPPH activities than gold nanoparticles and methanol extract of the strain. The silver nanoparticles showed higher antimicrobial activity than gold nanoparticles and petroleum ether extract of the strain. Thus, Thraustochytrium kinnei is proven to be promising for synthesis of silver nanoparticles with high antioxidant and antimicrobial activity.

This work studied the antioxidant and anti-colorectal cancer properties of a potential strain of thraustochytrids, Schizochytrium sp. (SMKK1), isolated from mangrove leaf litter. The biomass was extracted with methanol and screened for antioxidant activity using six different assays. The extract exhibited the highest total antioxidant activity (87.37 ± 1.22%) and the lowest nitric oxide radical (75.12 ± 2.22%), and the activity increased with the concentration of the extract. The methanolic extract was further tested for in vitro cytotoxicity on the colon cancer cell line (HT29). The extract was also analyzed for polyunsaturated fatty acids using GC-MS. The five predominant HTVS-based compounds, viz., arachidonic acid, linolenic acid (alpha-linolenic acid and gamma-linolenic acid), eicosapentaenoic acid, and docosahexaenoic acid, were identified in the extract, and these were tested against the colon cancer protein IGF binding (IGF-1) using the in silico docking method. The results revealed that all the five compounds were capable of destroying the colon oncoprotein responsible for anti-colon carcinogen, based on activation energy and also good hydrogen bond interaction against IGF binding proteins. Of the compounds, docosahexaenoic acid was the most effective, having a docking score of −10.8 Kcal/mol. All the five fatty acids passed the ADMET test and were hence accepted for further clinical trials towards the development of anticancer drugs.

This work studied the antioxidant and anti-breast cancer properties of hyaluronidase, extracted from a potential marine strain, Staphylococcus aureus (CASMTK1), isolated from Parangipettai coastal waters in southeast coast of India. The Staphylococcal enzyme production was tested under different carbon and nitrogen sources; and recorded the maximum production when the microbial strain was cultured with starch as the carbon source and ammonium sulphate as the inorganic nitrogen source with the enzyme production of 92.5 U/mL and 95.0 U/mL, respectively. The hyaluronidase enzyme production was also tested in different pH and temperature; and recorded the maximum yield of 102.5 U/mL in pH 5 and that of 95.5 U/mL in 45 °C. The partially purified enzyme was subjected to FTIR and FT Raman technique and found the presence of the amide- I and II, Carboxyl, N-H bending, C-H stretching and α-helices and β-sheet proteins between wave number 1500–1700 cm⁻¹. The partially purified enzyme also exhibited strong antioxidant and in-vitro breast cancer properties. The enzyme showed the highest hydroxyl radical scavenging activity of 79% at the 50 µg/mL concentration, and this activity increased in a dose-dependent manner. The enzyme inhibited proliferation of the breast cancer cell line of MCF-7, and it caused 100% cell death at the concentration of 80 µg/mL. The enzyme generated capacity of producing free radicles that damage the cancer cells, and this effect was very nearer to the standard drug, paclitaxel. The enzyme damaged the cancer cells and induced apoptosis in 78% of cancer cells as evident by condensed or fragmented chromatin at 40 µg/mL. Further purification of the enzyme, analysis of its molecular aspects, and elucidation of exact mechanisms of its biological activities will throw new light on the utility of staphylococcal hyaluronidase in anticancer chemotherapy.

This study investigated seasonal variations of thraustochytrids in rhizosphere soil collected from two mangrove species Rhizophora apiculata and Avicennia marina in natural and planted mangrove stands. Thraustochytrid counts were higher in the natural mangrove stand than in the planted site. The counts varied seasonally, being highest in the post-monsoon season followed by summer, monsoon, and pre-monsoon. Thraustochytrid counts exhibited positive correlations (p < 0.01) with counts of Total heterotrophic bacteria (THB), azotobacters, actinobacteria, fungi, yeasts, and Trichoderma. However, a negative correlation was observed with cyanobacteria. The counts also had positive correlation with silt, clay, nitrogen, phosphorus, potassium, chromium, copper, magnesium, cadmium, zinc and redox potential, but, negative correlations with temperature, pH, pore water salinity, total organic carbon and sand content of the soil samples. In the present study, 113 thraustochytrid strains were isolated from mangrove habitats. However, only 48 pure cultures survived after being sub-cultured three times. Based on survivability, color, and shape, two isolates from each sampling site in each season were selected. The predominant 24 isolates were identified based on their morphological, and molecular characteristics and were classified under five genera: Thraustochytrium, Schizochytrium, Botryochytrium, Parietichytrium, and Aurantiochytrium. Among the isolates, Aurantiochytrium sp. (AKTSK-06) produced the highest biomass of 15.71 g/L in the post-monsoon season (January-March, 2023), and Aurantiochytrium sp. (PVTSK-03) accumulated the highest lipid content of 61.33%. Thraustochytrids were found to contain Omega-3 poly unsaturated fatty acids (PUFAs), such as EPA up to 8.89% in Aurantiochytrium sp. (VRTSK-01), DPA up to 9.65% in Aurantiochytrium sp. (AKTSK-03), and DHA up to 47.46% in Aurantiochytrium sp. (AKTSK-06). Thus, mangroves provide an ideal ecological niche for thraustochytrids with an abundant supply of omega-3 fatty acids for potential industrial applications.