In vitro biological activity of Hydroclathrus clathratus and its use as an extracellular bioreductant for silver nanoparticle formation

The adaptive nature of algae results in producing unique chemical components that are gaining attention due to their efficiency in many fields and abundance. In this study, we screened the phytochemicals from the brown alga Hydroclathrus clathratus and tested its ability to produce silver nanoparticles (AgNPs) extracellularly for the first time. Lastly, we investigated its biological activity against a variety of bacteria. The biosynthesized nanoparticles were characterized by UV-visible spectroscopy, Fourier-transform infrared spectroscopy, dynamic light scattering, transmission electron microscopy, and energy-dispersive spectroscopy. The biological efficacy of AgNPs was tested against eighteen different bacteria, including seven multidrug-resistant bacteria. Phytochemical screening of the alga revealed the presence of saturated and unsaturated fatty acids, sugars, carboxylic acid derivatives, triterpenoids, steroids, and other components. Formed AgNPs were stable and ranged in size between 7 and 83 nm and presented a variety of shapes. Acinetobacter baumannii, Staphylococcus aureus, Methicillin-resistant S. aureus (MRSA), and MDR A. baumannii were the most affected among the bacteria. The biofilm formation and development assay presented a noteworthy activity against MRSA, with an inhibition percentage of 99%. Acknowledging the future of nano-antibiotics encourages scientists to explore and enhance their potency, notably if they were obtained using green, rapid, and efficient methods.

Taxonomic reassessment of the Indo-Pacific Scytosiphonaceae (Phaeophyceae): Hydroclathrus rapanuii sp. nov. and Chnoospora minima from Easter Island, with proposal of Dactylosiphon gen. nov. and Pseudochnoospora gen. nov.

A new and putatively endemic species ofHydroclathrus,Hydroclathrus rapanuii, is described from the geographically isolated Easter Island in the southeastern Pacific based on morphological and molecular phylogenetic data. It is distinguished from otherHydroclathrusby thalli of unevenly furrowed thin membranes, and angular, block-like plurangial sori. Our phylogenetic analyses indicated thatH. rapanuiiis closely related to the generitypeHydroclathrus clathratus. We also report on the morphology and phylogeny ofChnoospora minimafrom Easter I. and elsewhere in the Indo-Pacific Ocean, noting the previously unreported presence of hollow portions in its medulla. Although not collected from Easter I., we herein propose the recognition of two new genera,Dactylosiphongen. nov. andPseudochnoosporagen. nov., based on our three-gene phylogeny and their known morphologies and anatomies.Dactylosiphonis based on the three species currently assigned toColpomenia(C. bullosa,C. durvillei, andC. wynnei) that are genetically and morphologically (i.e. thalli with erect and finger-like tubes arising from a common saccate base) distinct from other members ofColpomenia. The monotypic genusPseudochnoosporais represented by the decumbent, branching, and inter-adhesive species currently known asChnoospora implexa. With the above proposals, we further increase the genus-level diversity of Scytosiphonaceae in the Indo-Pacific Ocean.

Uji Aktivitas Antioksidan pada Makro Alga Coklat Hydroclatrus clathratus (C. Agardh) Hower dan Padina minor Yamada

Makro alga cokelat merupakan salah satu sumber senyawa bioaktif, seperti antioksidan. Antioksidan merupakan zat yang dapat melawan pengaruh bahaya dari radikal bebas yang terbentuk sebagai hasil metabolisme oksidatif, yaitu hasil dari reaksi-reaksi kimia dan proses metabolik yang terjadi dalam tubuh. Penelitian ini bertujuan untuk menguji aktivitas antioksidan pada alga cokelat Hydroclathrus clathratus (C. Agardh) Hower dan Padina minor Yamada yang diambil dari perairan Tongkeina kota Manado dan perairan Selat Lembeh kota Bitung dengan menggunakan metode DPPH (1,1-difenil-2-pikrilhidrazil. Hasil penelitian dari ekstrak pigmen dalam PE pada makro alga H. clathratus (C. Agardh) Hower dan P. Minor Yamada memiliki aktivitas antioksidan yang lebih tinggi dibandingkan dengan ekstrak dalam etanol. Semakin kecil nilai absorban maka semakin tinggi nilai inhibisi dimana aktivitas antioksidan pada ekstrak semakin tinggi. Ekstrak yang digunakan memiliki nilai inhibisi yang mendekati dengan nilai inhibisi Kontrol yang digunakan yaitu asam askorbat dan tokoferol.

DIVERSITY OF ANTIBACTERIAL COMPOUNDS FROM EUCHEUMA SERRA, HALIMEDA OPUNTIA, AND HYDROCLATHRUS CLATHRATUS

Fourteen compounds were isolated from acetone extracts of three species of seaweeds (Eucheuma serra, a red seaweed, Halimeda opuntia, a green seaweed, and Hydroclathrus clathratus, a brown seaweed) using bioautographic TLC methods and identified using GC-MS. From Eucheuma serra were isolated 8 compounds (3 fatty acids, 3 steroids, and 2 aldehyds). Only two compounds of fatty acid camefrom Halimeda opuntia, whereas Hydroclathrus clathratus produced 6 compounds (4 fatty acids, one compound each of steroid and ether). All isolated single compoundswere tested for their antibacterial activities by the agar diffusion method against the Gram-positive bacteria Staphylococcus aureus, Bacillus subtilis and Streptococcusfaecalis, and the Gram-negative bacteria Echerichia coli, Pseudomonas aeruginosa and Salmonella typhimurium. All 14 compounds showed activity against Gram-positivebacteria, especially Bacillus subtilis, and only 2 compounds showed activity against Gram-negative bacteria Escherichia coli. Nine compounds showed activity against Staphylococcus aureus, and 4 compounds showed activity against Streptococcusfaecalis. All compounds were not active against Pseudomonas aeruginosa andSalmonella typhimurium bacteria. This study indicated that there is indeed a diversityboth in kinds and in molecular structures of the antibacterial substances.

Cellulose Contents of Some Abundant Indian Seaweed Species

Crude cellulose as well as α- and β-celluloses were estimated in thirty-four seaweed species of fifteen orders of Chlorophyta, Phaeophyta and Rhodophyta of Indian waters. The greatest yields of crude cellulose and α-cellulose were obtained from Chaetomorpha aerea (approx. 20.0% and 18.5%, respectively), and of β-cellulose (approx. 3.1%) from Caulerpa imbricata. The lowest crude cellulose, and α-and β-contents were recorded for the calcareous red alga Liagora indica (approx. 0.90%, 0.70% and 0.10%, respectively). There was little variation in cellulose content among the brown algae, while wide variations in the yields were found in the green and red algae. The present work contributes to the repertoire of 67 Indian seaweed species studied to now for their cellulose contents in our laboratory. The combined studies highlight that Chaetomorpha aerea, Acrosiphonia orientalis, Caulerpa taxifolia, Sargassum tenerrimum, Hydroclathrus clathratus and Gelidiella acerosa possess relatively high (>10%) cellulose contents, which could be of potential utility.