Studies on Spirulina Species NCIM 5143 for Microbial Fuel Cell Applications
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2023
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Abstract
This study utilizes Spirulina species NCIM 5143 procured from National Collection of Industrial Microorganisms, Pune, India. The phylogenetic analysis from 16S rRNA revealed its identity closer to Spirulina subsalsa BGLR6. The species was cultured in inorganic Zarrouk medium supplemented with trace elements in white light of 2500 lux at temperature of 32°C at 180 revolutions per minute. The specific growth rate and doubling time were found to be 0.0771 day-1 and 8.98 days respectively. The species was found to be a helical filament in structure with a diameter of 3 μm and pitch length of 1 μm. It exhibited gliding motility and moved towards light exhibiting phenomenon of positive phototaxis. This property influences the pattern of biofilm formation by the cyanobacteria and the configuration of filamentous cells within it, depending on the direction of illumination. The static culture always formed a network of filaments on walls that developed into biofilms over time and stuck to the walls. This natural biofilm formation capacity was utilized and the wet weight was inoculated into an H- type biofuel cell setup, leading to the formation of a biofilm over the electrodes. Interestingly, a subpopulation of bacteria was detected in the vicinity of the Spirulina filaments, and a few cells were directly attached to the filament structures. This close physical association indicates that crucial metabolite and nutrient exchange might occur between the host and bacterial cells. Four distinct heterotrophic colonies were isolated and identified through 16S rRNA sequencing as Halomonas saliphila, Halomonas campaniensis, Alcanivorax pacificus, and Pelagibacterium lentulum. We inferred, that these pure culture strains were the dominant members of the Spirulina-associated bacterial community as they could form colonies on the zarrouk medium plate devoid of any organic carbon source, thriving on residual extracellular organic carbon and metabolites exuded by the phototrophic host (Spirulina). These associations indicate a copiotrophic habitat typical of a phytoplankton bloom or matured phototrophic biofilm. We believe that this combination of predominant bacterial species isolated by us might be involved in efficient carbon and nitrogen cycling assisting the sustained growth of the host cyanobacterium (Spirulina subsalsa).
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Supervisors: Goswami, Pranab and Achalkumar, A S