Multidisciplinary Evidences that Synechocystis PCC6803 Exopolysaccharides Operate in Cell Sedimentation and Protection against Salt and Metal Stresses

Abstract

Little is known about the production of exopolysaccharides (EPS) in cyanobacteria, and there are no genetic and physiological evidences that EPS are involved in cell protection against the frequently encountered environmental stresses caused by salt and metals. We studied four presumptive EPS production genes, sll0923, sll1581, slr1875 and sll5052, in the model cyanobacterium Synechocystis PCC6803, which produces copious amounts of EPS attached to cells (CPS) and released in the culture medium (RPS) as shown here. We show that sll0923, sll1581, slr1875 and sll5052 are all dispensable to the growth of all corresponding single and double deletion mutants in absence of stress. Furthermore, we report that sll0923, sll1581 and slr1875 unambiguously operate in the production of both CPS and RPS. Both sll1581 and slr1875 are more important than sll0923 for CPS production, whereas the contrary is true for RPS production. We show that the most EPS-depleted mutant, doubly deleted for sll1581 and slr1875, lacks the EPS mantle that surrounds WT cells and sorbs iron in their vicinity. Using this mutant, we demonstrate for the first time that cyanobacterial EPS directly operate in cell protection against NaCl, CoCl2, CdSO4 and Fe-starvation. We believe that our EPS-depleted mutants will be useful tools to investigate the role of EPS in cell-to-cell aggregation, biofilm formation, biomineralization and tolerance to environmental stresses. We also suggest using the fast sedimenting mutants as biotechnological cell factories to facilitate the otherwise expensive harvest of the producer cell biomass and/or its separation from products excreted in the growth media.

Ethylene Regulates the Physiology of the Cyanobacterium Synechocystis sp. PCC 6803 via an Ethylene Receptor

“…For instance, motility, biofilm formation, and cell sedimentation of Synechocystis are dependent on both type IV pili and EPSs (Bhaya et al, 1999(Bhaya et al, , 2000Burriesci and Bhaya, 2008;Jittawuttipoka et al, 2013). Thus, ethylene may alter various physiological responses through alterations in extracellular characteristics via changes in EPSs and type IV pili.…”

“…To further study this, we used qRT-PCR to analyze the effect of disrupting SynEtr1 on the transcript abundance of slr1875, sll1581, sll5052, and sll0923 (Fig. 4D), which encode proteins thought to be involved in EPS production (Jittawuttipoka et al, 2013). Disruption of SynEtr1 led to an increase in slr1875 and a small decrease in sll5052 (P , 0.05).…”

“…At this time, we first visually inspected the layer of cells at the bottom of the tube and then assayed biofilm formation using Crystal Violet. Cell sedimentation assays were performed as described by Jittawuttipoka et al (2013). For this, 2 mL of cells was divided into aliquots in test tubes and maintained with no agitation for 4 d. The extent of sedimentation was then evaluated visually.…”

Production of exopolysaccharide by Rhizobium leguminosarum bv. trifolii and its role in bacterial attachment and surface properties

“…Similar results were reported by Planchon et al (2013), who noticed that the Synechocystis cells, which had a greater EPS layer, exhibited more negative electrophoretic mobility (and thus zeta potential). Moreover, Jttawuttipoka et al (2013) postulated that the zeta potential measurement could even facilitate finding EPS-defective mutants. Using the Rt24.2 strain, we have indicated a correlation between the amount of EPS present in the culture and the relative zeta potential value (Fig.…”

Isolation, characterization and localization of extracellular polymeric substances from the cyanobacteriumArthrospira platensisstrain MMG-9

“…EPS provide protection from various biotic and abiotic stresses and facilitate the attachment of the organism to a solid substrate (Palmer et al, 2007;Pereira et al, 2009;Jittawuttipoka et al, 2013). Generally, EPS are categorized into three types: sheaths, capsules and mucilage, based on their location, structure and consistency.…”