Isolation, Identification and Characterisation of Seaweed-Associated Bacteria
Seaweeds are a large and diverse group of photoautotrophs which offer a nutrient-rich environment for microbial communities (Karthick & Mohanraju, 2018). Bacteria are ubiquitously present as either epiphytes on the seaweed surface, or are symbiotically associated with the living host cells. The associated bacterial communities have been reported to play an important role in seaweed development, and in protection from pathogens and a wide range of abiotic stress factors. Seaweed-associated bacterial communities can also degrade polysaccharides, produce biologically active compounds and are capable of inhibiting other bacterial growth.
The objective of my summer dissertation is to isolate, identify and characterise the cultivable bacteria associated with the three tropical seaweeds (Gracilaria sp., Hypnea sp., and Chaetomorpha sp.) growing along Covelong coast near Chennai. The algal thalli were collected from intertidal rocks, put into ziplock plastic bags and brought to the laboratory within an hour of collection. They were cleaned using a paint brush and rinsed with sterile water to remove the visible epiphytes. The algal tissues were then crushed using a sterilised glass homogeniser and were serially diluted (10-2) in the filtered and autoclaved seawater. The extract was spread-plated on Zobell Marine Agar (ZMA) and de Man, Rogosa and Sharpe (MRS) agar, and incubated at 30 ºC for 24 hours. In total, 22 bacteria from ZMA and 1 bacterium from MRS plates were isolated based on their colony morphologies. Furthermore, these isolates were purified by successive re-streaking on respective plates.
The isolates were screened for their UV absorbance potential, anti-vibrio activities and pH reducing capabilities. Only those isolates showing these characteristics will be identified through polyphasic taxonomy and if any new species/strains are found, that will be reported.
Keywords: Seaweed, marine bacteria, antimicrobial activities, probiotics, lactic acid bacteria.