Extracellular polymeric substances in psychrophilic cyanobacteria: A potential bioflocculant and carbon sink to mitigate cold stress

Abstract

Cyanobacteria dominate microbiota in ice-based habitats and contend with extreme fluctuation in temperature and lack of liquid water, which poses severe limitations (freezing and desiccation stress) to their growth and survival. Decline in carbon sinks would result in faster accumulation of CO2 in the atmosphere and is expected to increase by 18.05% between 2022 and 2050 contributing to future climate change. Anthropogenic CO2 emissions could be even much higher if terrestrial biosphere would not pull off it as a sink by absorbing 33 ± 9% CO2. Cyanobacterial bio-sequestration in colder habitats is critical because of less water body turnover due to low temperature. These organisms show amazing structural and functional diversity adopting cyclic electron flow (CEF) for sustenance under lower temperature ecosystem. CEF enhances ATP: NADPH ratio during photosynthesis and balances the reductant prerequisites of biosynthesis while maintaining the redox balance of CEF. ATP-binding cassette dependent is an important pathway for production of extracellular polymeric substances (EPS) in case of capsular polysaccharides. The review proposes NDH-1MS’ an important energy yielding complex capable of optimizing CO2 acquisition and photosynthesis when the cells are under cold stress. The review also highlights the formidable sub-cellar role of EPS, influencing cyanobacterial physiology and survival in cold ecosystems.