Many microbial photoautotrophs depend on heterotrophic bacteria for accomplishing essential functions. Environmental changes, however, could alter or eliminate such interactions. We investigated the effects of changing pCO2 on gene transcription in co-cultures of 3 strains of picocyanobacteria (Synechococcus strains CC9311 and WH8102 and Prochlorococcus strain MIT9312) paired with the ‘helper’ bacterium Alteromonas macleodii EZ55. Co-culture with cyanobacteria resulted in a much higher number of up- and down-regulated genes in EZ55 than pCO2 by itself. Pathway analysis revealed significantly different transcription of genes involved in carbohydrate metabolism, stress response, and chemotaxis, with different patterns of up- or down-regulation in co-culture with different cyanobacterial strains. Gene transcription patterns of organic and inorganic nutrient transporter and catabolism genes in EZ55 suggested resources available in the culture media were altered under elevated (800 ppm) pCO2 conditions. Altogether, changing transcription patterns were consistent with the possibility that the composition of cyanobacterial excretions changed under the two pCO2 regimes, causing extensive ecophysiological changes in both members of the co-cultures. Additionally, significant downregulation of oxidative stress genes in MIT9312/EZ55 cocultures at 800 ppm pCO2 were consistent with a link between the predicted reduced availability of photorespiratory byproducts (i.e., glycolate/2PG) under this condition and observed reductions in internal oxidative stress loads for EZ55, providing a possible explanation for the previously observed lack of “help” provided by EZ55 to MIT9312 under elevated pCO2. If similar broad alterations in microbial ecophysiology occur in the ocean as atmospheric pCO2 increases, they could lead to substantially altered ecosystem functioning and community composition.
Picocyanobacteria (mainly Synechococcus and Prochlorococcus) contribute significantly to ocean’s primary production. Toxin-Antitoxin (TA) systems present in bacteria and archaea are known to regulate cell growth in response to environmental stresses. However, little is known about the presence of TA systems in picocyanobacteria. This study investigated complete genomes of Synechococcus and Prochlorococcus to understand the prevalence of TA systems in picocyanobacteria. Using the TAfinder software, Type II TA systems were predicted in 27 of 33 (81%) Synechococcus strains, but none of 38 Prochlorococcus strains contain TA genes. Synechococcus strains with larger genomes tend to contain more putative type II TA systems. The number of TA pairs varies from 0 to 42 in Synechococcus strains isolated from various environments. A linear correlation between the genome size and the number of putative TA systems in both coastal and freshwater Synechococcus was established. In general, open ocean Synechococcus contain no or few TA systems, while coastal and freshwater Synechococcus contain more TA systems. The type II TA systems inhibit microbial translation via ribonucleases and allow cells to enter the “dormant” stage in adverse environments. Inheritance of TA genes in freshwater and coastal Synechococcus could confer a recoverable persister mechanism important to survive in variable environments.
more » « less- Award ID(s):
- 1829888
- NSF-PAR ID:
- 10485636
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- The ISME Journal
- Volume:
- 14
- Issue:
- 11
- ISSN:
- 1751-7362
- Format(s):
- Medium: X Size: p. 2843-2850
- Size(s):
- ["p. 2843-2850"]
- Sponsoring Org:
- National Science Foundation
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