Isolation and characterization of bioflocculant-producing bacteria from water and bottom sediment of mud crab, Scylla sp. grow-out pond Shahadat Hossain1, Zuhayra Nasrin1, Rohisyamuddin Othman1, Helena Khatoon4, Zahidul Islam2, Tashrif Mahmud Minhaz3, Amyra Suryatie Kamaruzzan1, Nor Azman Kasan*1
1Higher Institution Centre of Excellent (HICoE), Institute of Tropical Aquaculture and Fisheries, Universiti Malaysia Terengganu, 21030 Kuala Nerus, Terengganu, Malaysia.
2Marine Fisheries and Technology Station, Bangladesh Fisheries Research Institute, Cox^s Bazar Sadar-4700, Cox^s Bazar, Bangladesh.
3Freshwater Sub Station, Bangladesh Fisheries Research Institute, Saidpur-5310, Nilphamari, Bangladesh.
2Marine Fisheries and Technology Station, Bangladesh Fisheries Research Institute, Cox^s Bazar Sadar-4700, Cox^s Bazar, Bangladesh.
4Chattogram Veterinary and Animal Sciences University, Chattogram 4225, Bangladesh
*Corresponding author: Nor Azman Kasan
Email: norazman[at]umt.edu.my
Abstract
Biofloc technology (BFT), which is widely used and one of the most cost-effective, environmentally friendly, and profitable farming technologies, but not well-known or attempted for mud crab farming due to cannibalism, high labor expenses, and complex processes. As cannibalism does not occur in mud crab zoea larval stages, this technology has the potential to deliver greater survivability and growth performance by removing hazardous compounds from the culture water. This study aimed to isolate and characterize bioflocculant-producing bacteria (BPB) from water and sediment of a mud crab, Scylla sp. grow-out pond to apply them as inoculum at mud crab hatchery operation, especially for zoea larval stages. The sampling was conducted following standard protocol from randomly selected three different ponds. BPB were isolated from the water and sediment using the serial dilution, spread plate, and streaking plate methods on Zobell marine agar. Yeast peptone agar (YPG), and enrichment media were used to screen the bacteria showing biofloc forming ability. Morphological, biochemical, and 16s rRNA molecular approaches were performed to screen the bacteria, where the flocculating activity of the species was determined using the kaolin suspension method. A total of 88 isolates were found from both water (82 isolates) and sediment (6 isolates) samples and 18 bacteria isolates showed floc forming characteristics like slimy and milky appearance on YPG agar and enrichment media. These 18 isolates were identified as Bacillus cereus, Bacillus tropicus , Bacillus infantis , Vibrio alginolyticus , Priestia flexa, and Micrococcus luteus, following 16s rRNA sequencing. The species B. tropicus showed a maximum of 94.99% flocculation activity on the kaolin clay suspension, whereas M. luteus showed a minimum of 74.81% flocculation activity. This study indicated that all the identified BPB species potentially play an important role in the application of different flocculation processes.
