Cyanobacterial reuse of extracellular organic carbon in microbial mats.
Cyanobacterial organic matter excretion is crucial to carbon cycling in many microbial communities, but the nature and bioavailability of this C depend on unknown physiological functions. Cyanobacteria-dominated hypersaline laminated mats are a useful model ecosystem for the study of C flow in complex communities, as they use photosynthesis to sustain a more or less closed system. Although such mats have a large C reservoir in the extracellular polymeric substances (EPSs), the production and degradation of organic carbon is not well defined. To identify extracellular processes in cyanobacterial mats, we examined mats collected from Elkhorn Slough (ES) at Monterey Bay, California, for glycosyl and protein composition of the EPS. We found a prevalence of simple glucose polysaccharides containing either α or β (1,4) linkages, indicating distinct sources of glucose with differing enzymatic accessibility. Using proteomics, we identified cyanobacterial extracellular enzymes, and also detected activities that indicate a capacity for EPS degradation. In a less complex system, we characterized the EPS of a cyanobacterial isolate from ES, ESFC-1, and found the extracellular composition of biofilms produced by this unicyanobacterial culture were similar to that of natural mats. By tracing isotopically labeled EPS into single cells of ESFC-1, we demonstrated rapid incorporation of extracellular-derived carbon. Taken together, these results indicate cyanobacteria reuse excess organic carbon, constituting a dynamic pool of extracellular resources in these mats.
Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, CA, USA.
Rhona K
RK
Stuart
Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, CA, USA.
Xavier
X
Mayali
Exobiology Branch, NASA Ames Research Center, Moffett Field, CA, USA.
Jackson Z
JZ
Lee
Exobiology Branch, NASA Ames Research Center, Moffett Field, CA, USA.
R
R
Craig Everroad
Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, CA, USA.
Mona
M
Hwang
Exobiology Branch, NASA Ames Research Center, Moffett Field, CA, USA.
Brad M
BM
Bebout
Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, CA, USA.
Peter K
PK
Weber
Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, CA, USA.
Jennifer
J
Pett-Ridge
Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, CA, USA.
Michael P
http://orcid.org/0000-0002-2479-5480
MP
Thelen
D018441:Biofilms; D002140:California; D002244:Carbon / Q000378:metabolism*; D057486:Carbon Cycle; D000458:Cyanobacteria / Q000378:metabolism*; D017753:Ecosystem; D006031:Glycosylation; D006863:Hydrogen-Ion Concentration; D010788:Photosynthesis; D011134:Polysaccharides / Q000737:chemistry; D020543:Proteome
D011134:Polysaccharides; D020543:Proteome; D002244:Carbon