Abstract
Thin, filamentous, non-heterocystous, benthic cyanobacteria (Subsection III) from some marine, lacustrine and thermal environments aggregate into macroscopic cones and conical stromatolites. We investigate the uptake and storage of inorganic carbon by cone-forming cyanobacteria from Yellowstone National Park using high-resolution stable isotope mapping of labeled carbon (H13CO3 −) and immunoassays. Observations and incubation experiments in actively photosynthesizing enrichment cultures and field samples reveal the presence of abundant cyanophycin granules in the active growth layer of cones. These ultrastructurally heterogeneous granules rapidly accumulate newly fixed carbon and store 18% of the total particulate labeled carbon after 120 mins of incubation. The intracellular distribution of labeled carbon during the incubation experiment demonstrates an unexpectedly large contribution of PEP carboxylase to carbon fixation, and a large flow of carbon and nitrogen toward cyanophycin in thin filamentous, non-heterocystous cyanobacteria. This pattern does not occur in obvious response to a changing N or C status. Instead, it may suggest an unusual interplay between the regulation of carbon concentration mechanisms and accumulation of photorespiratory products that facilitates uptake of inorganic C and reduces photorespiration in the dense, surface-attached communities of cyanobacteria from Subsection III.
Highlights
Cyanobacteria fix inorganic carbon using the enzyme ribulose 1,5 bi-phosphate carboxylase oxygenase (RuBisCO) [1] and commonly encapsulate this enzyme in polyhedral inclusions called carboxysomes to improve the carboxylation efficiency [2,3,4,5]
Cyanophycin, a non-protein, non-ribosomally produced branched polypeptide is composed of an aspartic acid backbone and (L)-arginine side chains [6,7,8] and is commonly found in stationary phase cells [9,10,11]
Less is known about cyanophycin and other cellular inclusions in non-heterocystous cyanobacteria [14] and filamentous, non-heterocystous benthic cyanobacteria (Subsection III) [15], the latter are common in various marine and terrestrial benthic environments [16,17,18,19]
Summary
Cyanobacteria fix inorganic carbon using the enzyme ribulose 1,5 bi-phosphate carboxylase oxygenase (RuBisCO) [1] and commonly encapsulate this enzyme in polyhedral inclusions called carboxysomes to improve the carboxylation efficiency [2,3,4,5]. We track the flow of labeled carbon in cone-forming cyanobacteria by incubation experiments, isotopic labeling and nano-scale secondary ion mass spectrometry (SIMS).
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