A P Lipton

Sea grasses are marine angiosperms specially adopted to establish and grow in coastal ecosystems. The structural components of leaves, rhizomes and roots trap and store both sediments and nutrient inputs leading to high biodiversity and productivity in sea grass meadows. Their dynamic nutrient cycling processes attract microbial communities and the surface areas of sea grasses host complex assemblages of bacteria. Such bacterial assemblages modify their micro environment and enhance formation of biofilms. These biofilms interact and influence the overall health status of the host sea grass by assisting in their defense against colonization by invaders, fouling and grazing organisms. This colonization is considered essential for the normal growth and development of sea grass as well as synthesis of defense metabolites to protect from predators and pathogens. Thus these metabolites are not only important for the health and establishment of sea grasses but also form lead molecules with beneficial applications, including. Developing novel strategies against managing insect pests and mosquitoes. The study surveyed about 70km of coastline stretch of Kanyakumari district, India (8° 05' 24.29" N and 77° 32' 18.28" E). Sample collection was selected based on the availability of sea grass beds. For microbial analysis, the blades of Halodule pinifolia and Syringodium isoetifolium were aseptically collected in plastic bags, kept in ice boxes and transported to the laboratory for analysis. To isolate the biofilm bacteria, five replicate sea grass samples from each species of healthy sea grass blades were collected aseptically underwater in sterile screw cap centrifuge tubes. After incubation (37°C for 24h) in a modified media consisting sea grass extract, bacterial colonies grew out onto the agar surface along sea grass blade. Bacteria were characterized by standard microbiological methods. Dominant strains were subsequently characterized using molecular methods. For mosquito larvicidal activity, the IVinstar larvae of Aedes aegyptii were used. For this, egg cards were incubated and reared in water-filled trays. Insect repellent activity was examined using 14 to 21 day old (adult) storage pest, Tribolium castaneum. Repellency was evaluated using Tukey Comparative test using Orgin software.

Results indicated Staphylococcus, Pseudomonas, Bacillus and E. coli formed biofilm in H. pinifolia blades. In S. isoetifolium, strains of Micrococcus, Staphylococcus, Vibrio, Pseudomonas and Bacillus were recorded. Repellent activity of Tribolium castaneum was noted in both the sea grass extracts from 1.0% onwards after 5h. The mosquito larvicidal activity and pest repellent activity were high in H. pinifolia extracts than S. isoetifolium. Total mortality of Aedes aegypti larvae was noted within 24 and 48 hours respectively in 150 ppm and 100 ppm concentrations in H. pinifolia extract with LC50 value of 55.407 ppm (24h) and 29.592ppm (48h). Chemical analysis of H. pinifolia extract revealed the presence of a predominant tannin (1, 2- benzenedicarboxylic acid), phenol terpenes [1-phenyl-3-(bis (methoxy carbonyl) methyl), hex-1-en-4, 2,2,6-trimethyl 1-5-hepten-3-one], flavanoid and 2H-pyran-6-carboxylic acid apart from saturated and unsaturated fatty alcohols and acids. The extract of S. isoetifolium consisted of terpene hexanedioic acid, di-isooctyl phthalate, isopropyl myristate, fatty acids such as decanol, tetra-decanol, fatty alcohols and alkaloids.

The study underlines the importance of biofilm forming bacteria and phytochemicals present in sea grasses and their utilities. These data will form the baseline information for understanding the bacteria-sea grass interactions and in the field of marine biotechnology.

Audience Take Away:

• Research in Marine plants is still at an infant stage. This presentation is expected to kindle research interest among scientists, scholars and students to pursue specific further studies.
• The research methodologies used in the study right from preparation for collections of samples to the microbiological, chemical and structural analysis of compounds will be of much help to initiate suitable research.