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Title: Light Regimes Shape Utilization of Extracellular Organic C and N in a Cyanobacterial Biofilm

Abstract

Although it is becoming clear that many microbial primary producers can also play a role as organic consumers, we know very little about the metabolic regulation of photoautotroph organic matter consumption. Cyanobacteria in phototrophic biofilms can reuse extracellular organic carbon, but the metabolic drivers of extracellular processes are surprisingly complex. We investigated the metabolic foundations of organic matter reuse by comparing exoproteome composition and incorporation of 13C-labeled and 15N-labeled cyanobacterial extracellular organic matter (EOM) in a unicyanobacterial biofilm incubated using different light regimes. In the light and the dark, cyanobacterial direct organic C assimilation accounted for 32% and 43%, respectively, of all organic C assimilation in the community. Under photosynthesis conditions, we measured increased excretion of extracellular polymeric substances (EPS) and proteins involved in micronutrient transport, suggesting that requirements for micronutrients may drive EOM assimilation during daylight hours. This interpretation was supported by photosynthesis inhibition experiments, in which cyanobacteria incorporated N-rich EOM-derived material. In contrast, under dark, C-starved conditions, cyanobacteria incorporated C-rich EOM-derived organic matter, decreased excretion of EPS, and showed an increased abundance of degradative exoproteins, demonstrating the use of the extracellular domain for C storage. Sequence-structure modeling of one of these exoproteins predicted a specific hydrolytic activity thatmore » was subsequently detected, confirming increased EOM degradation in the dark. Associated heterotrophic bacteria increased in abundance and upregulated transport proteins under dark relative to light conditions. Taken together, our results indicate that biofilm cyanobacteria are successful competitors for organic C and N and that cyanobacterial nutrient and energy requirements control the use of EOM. IMPORTANCECyanobacteria are globally distributed primary producers, and the fate of their fixed C influences microbial biogeochemical cycling. This fate is complicated by cyanobacterial degradation and assimilation of organic matter, but because cyanobacteria are assumed to be poor competitors for organic matter consumption, regulation of this process is not well tested. In mats and biofilms, this is especially relevant because cyanobacteria produce an extensive organic extracellular matrix, providing the community with a rich source of nutrients. Light is a well-known regulator of cyanobacterial metabolism, so we characterized the effects of light availability on the incorporation of organic matter. Using stable isotope tracing at the single-cell level, we quantified photoautotroph assimilation under different metabolic conditions and integrated the results with proteomics to elucidate metabolic status. We found that cyanobacteria effectively compete for organic matter in the light and the dark and that nutrient requirements and community interactions contribute to cycling of extracellular organic matter.« less

Authors:
; ; ; ; ; ; ; ; ; ; ORCiD logo
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1342324
Report Number(s):
PNNL-SA-121065
Journal ID: ISSN 2150-7511; KP1601010
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: mBio (Online); Journal Volume: 7; Journal Issue: 3
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES

Citation Formats

Stuart, Rhona K., Mayali, Xavier, Boaro, Amy A., Zemla, Adam, Everroad, R. Craig, Nilson, Daniel, Weber, Peter K., Lipton, Mary, Bebout, Brad M., Pett-Ridge, Jennifer, and Thelen, Michael P. Light Regimes Shape Utilization of Extracellular Organic C and N in a Cyanobacterial Biofilm. United States: N. p., 2016. Web. doi:10.1128/mBio.00650-16.
Stuart, Rhona K., Mayali, Xavier, Boaro, Amy A., Zemla, Adam, Everroad, R. Craig, Nilson, Daniel, Weber, Peter K., Lipton, Mary, Bebout, Brad M., Pett-Ridge, Jennifer, & Thelen, Michael P. Light Regimes Shape Utilization of Extracellular Organic C and N in a Cyanobacterial Biofilm. United States. doi:10.1128/mBio.00650-16.
Stuart, Rhona K., Mayali, Xavier, Boaro, Amy A., Zemla, Adam, Everroad, R. Craig, Nilson, Daniel, Weber, Peter K., Lipton, Mary, Bebout, Brad M., Pett-Ridge, Jennifer, and Thelen, Michael P. 2016. "Light Regimes Shape Utilization of Extracellular Organic C and N in a Cyanobacterial Biofilm". United States. doi:10.1128/mBio.00650-16.
@article{osti_1342324,
title = {Light Regimes Shape Utilization of Extracellular Organic C and N in a Cyanobacterial Biofilm},
author = {Stuart, Rhona K. and Mayali, Xavier and Boaro, Amy A. and Zemla, Adam and Everroad, R. Craig and Nilson, Daniel and Weber, Peter K. and Lipton, Mary and Bebout, Brad M. and Pett-Ridge, Jennifer and Thelen, Michael P.},
abstractNote = {Although it is becoming clear that many microbial primary producers can also play a role as organic consumers, we know very little about the metabolic regulation of photoautotroph organic matter consumption. Cyanobacteria in phototrophic biofilms can reuse extracellular organic carbon, but the metabolic drivers of extracellular processes are surprisingly complex. We investigated the metabolic foundations of organic matter reuse by comparing exoproteome composition and incorporation of13C-labeled and15N-labeled cyanobacterial extracellular organic matter (EOM) in a unicyanobacterial biofilm incubated using different light regimes. In the light and the dark, cyanobacterial direct organic C assimilation accounted for 32% and 43%, respectively, of all organic C assimilation in the community. Under photosynthesis conditions, we measured increased excretion of extracellular polymeric substances (EPS) and proteins involved in micronutrient transport, suggesting that requirements for micronutrients may drive EOM assimilation during daylight hours. This interpretation was supported by photosynthesis inhibition experiments, in which cyanobacteria incorporated N-rich EOM-derived material. In contrast, under dark, C-starved conditions, cyanobacteria incorporated C-rich EOM-derived organic matter, decreased excretion of EPS, and showed an increased abundance of degradative exoproteins, demonstrating the use of the extracellular domain for C storage. Sequence-structure modeling of one of these exoproteins predicted a specific hydrolytic activity that was subsequently detected, confirming increased EOM degradation in the dark. Associated heterotrophic bacteria increased in abundance and upregulated transport proteins under dark relative to light conditions. Taken together, our results indicate that biofilm cyanobacteria are successful competitors for organic C and N and that cyanobacterial nutrient and energy requirements control the use of EOM. IMPORTANCECyanobacteria are globally distributed primary producers, and the fate of their fixed C influences microbial biogeochemical cycling. This fate is complicated by cyanobacterial degradation and assimilation of organic matter, but because cyanobacteria are assumed to be poor competitors for organic matter consumption, regulation of this process is not well tested. In mats and biofilms, this is especially relevant because cyanobacteria produce an extensive organic extracellular matrix, providing the community with a rich source of nutrients. Light is a well-known regulator of cyanobacterial metabolism, so we characterized the effects of light availability on the incorporation of organic matter. Using stable isotope tracing at the single-cell level, we quantified photoautotroph assimilation under different metabolic conditions and integrated the results with proteomics to elucidate metabolic status. We found that cyanobacteria effectively compete for organic matter in the light and the dark and that nutrient requirements and community interactions contribute to cycling of extracellular organic matter.},
doi = {10.1128/mBio.00650-16},
journal = {mBio (Online)},
number = 3,
volume = 7,
place = {United States},
year = 2016,
month = 6
}
  • Here it is becoming clear that many microbial primary producers can also play a role as organic consumers, we know very little about the metabolic regulation of photoautotroph organic matter consumption. Cyanobacteria in phototrophic biofilms can reuse extracellular organic carbon, but the metabolic drivers of extracellular processes are surprisingly complex. We investigated the metabolic foundations of organic matter reuse by comparing exoproteome composition and incorporation of 13C-labeled and 15N-labeled cyanobacterial extracellular organic matter (EOM) in a unicyanobacterial biofilm incubated using different light regimes. In the light and the dark, cyanobacterial direct organic C assimilation accounted for 32% and 43%, respectively,more » of all organic C assimilation in the community. Under photosynthesis conditions, we measured increased excretion of extracellular polymeric substances (EPS) and proteins involved in micronutrient transport, suggesting that requirements for micronutrients may drive EOM assimilation during daylight hours. This interpretation was supported by photosynthesis inhibition experiments, in which cyanobacteria incorporated N-rich EOM-derived material. In contrast, under dark, C-starved conditions, cyanobacteria incorporated C-rich EOM-derived organic matter, decreased excretion of EPS, and showed an increased abundance of degradative exoproteins, demonstrating the use of the extracellular domain for C storage. Sequence-structure modeling of one of these exoproteins predicted a specific hydrolytic activity that was subsequently detected, confirming increased EOM degradation in the dark. Associated heterotrophic bacteria increased in abundance and upregulated transport proteins under dark relative to light conditions. Taken together, our results indicate that biofilm cyanobacteria are successful competitors for organic C and N and that cyanobacterial nutrient and energy requirements control the use of EOM.« less
  • The relationship between adherence of bacteria to foreign bodies and their deposition of extracellular matrix was examined on glass and suture material. To quantitate bacterial adherence, uptake of ({sup 3}H)thymidine into bacterial DNA was analyzed. Corresponding amounts of extracellular matrix were measured by a new technique using ({sup 14}C)glucose incorporation. This study shows that ({sup 14}C)glucose preferentially labeled bacterial strains in proportion to biofilm production. The ratio of {sup 3}H{sup 14}C in high biofilm producers was 0.9 and in low producers it was 3.7. Radioactive identification of organisms as high and low producers was confirmed by electron microscopy. The resultsmore » presented here show that production and accumulation of biofilm over time is a stable characteristic in different strains of S. epidermidis. The use of ratios reflecting radiolabeling of bacteria and biofilm by ({sup 3}H)thymidine and ({sup 14}C)glucose, respectively, is a quantitative yet simple technique to assess extracellular matrix of different strains of S. epidermidis.« less
  • Rats were given constant intravenous infusions of (/sup 3/H)-leucine plus (1-/sup 14/C)-2-ketoisocaproate (KIC). Specific activities of plasma leucine and plasma KIC reached plateaus by two to three hours. /sup 3/H specific activity of KIC was 85% +/- 2% of that in leucine. /sup 14/C specific activity of leucine was 36% +/- 2% of that in KIC. The /sup 14/C//sup 3/H ratios in leucine and KIC were constant from the earliest sampling time (one hour) at 0.65 +/- 0.03 and 2.20 +/- 0.07, respectively. In various tissues, /sup 14/C//sup 3/H in free leucine and in tissue protein were approximately equal, butmore » in most organs these ratios were significantly greater than the ratio /sup 14/C//sup 3/H in plasma leucine. From these data we estimate that the fraction of leucine incorporated into protein in individual organs derived from extracellular KIC rather than extracellular leucine varies from zero (in liver and bone marrow) to 35% to 45% (in brain and heart), and comprises 12% in the body as a whole.« less
  • We report on the fabrication of plasma damage-free organic light-emitting devices (OLEDs) by using a mirror shape target sputtering (MSTS) technique. It is shown that OLEDs with Al cathode deposited by the MSTS show much lower leakage current (1x10{sup -5} mA/cm{sup 2}) at reverse bias of -6 V, compared to that (1x10{sup -1}-{approx}10{sup -2} mA/cm{sup 2} at -6 V) of OLEDs with Al cathodes grown by conventional dc magnetron sputtering. This indicates that there is no plasma damage, which is caused by the bombardment of energetic particles. This suggests that MSTS could be a useful plasma damage-free and low-temperature depositionmore » technique for both top- and bottom-emitting OLEDs and flexible displays.« less