Fine-structural and chemical analyses on inner and outer sheath of the cyanobacteriumGloeothece sp. PCC 6909

Abstract

Cells of the unicellular cyanobacterium Gloeothece sp. PCC 6909 are surrounded by an inner (enclosing 1-2 cells) and an outer (enclosing cell groups) sheath. Using conventional Epon-embedding in combination with ruthenium-red staining, the inner and outer sheaths appeared similar and displayed multiple bands of electron-dense subunits. However, embedding in Nanoplast resin to avoid shrinkage led to the detection of two distinct zones (inner and outer zone) each with several distinct layers. The zone delimited by the electron-dense thick inner sheath layer, and the zone enclosed by the thin electron-dense outer sheath layer, are composed of a homogeneous material of little electron-contrast. Whereas the outer zone appears to be of even contrast, the inner zone is characterized by a distinct electron-transparent layer. Element distribution analysis revealed that the electron-transparent layer contained relatively large amounts of sulfur, carbon, and oxygen but only little nitrogen. Inner and outer sheath fractions were isolated by differential mechanical cell breakage and centrifugation. The outer sheath fraction was less hydrated than the inner one. The two fractions differed little in their contents of uronic acids, carbohydrate and protein, although the outer sheath fraction contained less sulfate. A soluble polysaccharide with a chemical composition similar to that of inner and outer sheath fractions was also obtained from the culture supernatant.

Sheathless Mutant of Cyanobacterium Gloeothece sp. Strain PCC 6909 with Increased Capacity To Remove Copper Ions from Aqueous Solutions

“…Indeed, the acidic sugars are 35% more abundant in the RPS of the mutant, thus conferring a higher affinity for the positively charged copper ions, while the deoxysugars fucose and rhamnose were 28% more abundant in the RPS of the wild type, providing this polymer with a higher degree of hydrophobicity (5) and reducing its solubility and, as a consequence, its accessibility for copper ions. In the Gloeothece wild type, the compositions of the sheath and the released polysaccharide were significantly different, indicating that the RPS is not merely due to the solubilization of the external layer(s) of the sheath, as has been previously suggested for this organism (33), but that it probably arose from another biosynthetic process. It is also worth mentioning that the monosaccharidic composition of the sheath of the Gloeothece strain PCC 6909 wild type reported here (Table 1) differs qualitatively and quantitatively from that reported previously, performed with cells grown with different amounts of nitrate (or no nitrate at all) and at different temperatures (32,33), confirming that the growth conditions may play a significant role in determining the sheath composition, as was previously suggested (32).…”

“…In the Gloeothece wild type, the compositions of the sheath and the released polysaccharide were significantly different, indicating that the RPS is not merely due to the solubilization of the external layer(s) of the sheath, as has been previously suggested for this organism (33), but that it probably arose from another biosynthetic process. It is also worth mentioning that the monosaccharidic composition of the sheath of the Gloeothece strain PCC 6909 wild type reported here (Table 1) differs qualitatively and quantitatively from that reported previously, performed with cells grown with different amounts of nitrate (or no nitrate at all) and at different temperatures (32,33), confirming that the growth conditions may play a significant role in determining the sheath composition, as was previously suggested (32). The titration curves obtained for the sheath and the RPS of the wild type showed that only one functional group, with a pK a in the range of 5.5 to 6.9, and putatively assigned to carboxyl or phosphate groups (1,2,26), plays a significant role in their ion exchange properties toward cations.…”

“…The efficiency of cyanobacterial EPS in the removal of metal ions has been discussed previously, with an emphasis on the monosaccharidic composition of the polymer, the isolation of EPS, and the subsequent utilization with removal assays (5,8,21). Although the chemical composition of the sheaths of several cyanobacterial strains has been determined (14,15,32,33,38,39) and the importance of the capsules and RPS in the metal-removal process has been recognized (6), information about the exact contribution of each type of EPSs and/or functional group to the biosorption of the metal is still very limited.…”

Sulphate‐limited growth in the N2‐fixing unicellular cyanobacterium Gloeothece (Nägeli) sp. PCC 6909

“…The sheath is composed of different layers. The inner sheath encloses 1-2 cells whereas the outer sheath encloses cell groups (Tease et al, 1991). The sheath of Gloeothece is composed of complex heteropolysac-charides.…”

“…The sheath of Gloeothece is composed of complex heteropolysac-charides. A particular interesting property of the sheath is the presence of sulphated polysaccharides (Tease & Walker, 1987;Weckesser et al, 1987;Tease et at., 1991). Sulphated polysaccharides are common in eukaryotic algae {Percival, 1979) but are extremely rare among prokaryotes.…”