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Functional Profiling Of Metabolic Regulation In Marine Bacteria
Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science. (Marine Microbial Ecology)
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Oceans are powered by active, metabolically diverse microorganisms, which are important in regulating biogeochemical cycles on Earth. Most of the ocean surface is often limited by nutrients, influencing bacterial growth and activities. Bacterial adaptation to fluctuating environmental conditions involves extensive reprogramming, and redirection of bacterial metabolism and physiology. In this thesis, I investigated the molecular mechanisms of bacterial adaptation strategies to sustain their growth and survival, focusing on the regulation of gene and protein expression in heterotrophic marine bacteria.

Comparative proteomics analyses of the growth and non-growth conditions, uncovered central adaptations that marine bacteria employ to allow them to change their metabolism to support exponential growth in response to nutrients and to readjust to stationary phase under nutrient limitation. Our results highlight that during nutrient rich conditions three distinct bacteria lineages have great similarities in their proteome. On the other hand, we observed pronounced differences in behavior between taxa during stationary phase.

Analyses of the proteorhodopsin containing bacterium Vibrio sp. AND4 during starvation showed that significantly improved survival in the light compared to darkness. Notably, proteins involved in promoting cell vitality and survival had higher relative abundance under light. In contrast, cells in the dark need to degrade their endogenous resources to support their basic cellular demands under starvation. Thus, light strongly influences how PR-containing bacteria organize their molecular composition in response to starvation.

Study of alternative energy generation metabolisms in the Alphaproteobacteria Phaeobacter sp. MED193 showed that the addition of thiosulfate enhanced the bacterial growth yields. Concomitantly, inorganic sulfur oxidation gene expression increased with thiosulfate compared to controls. Moreover, thiosulfate stimulated protein synthesis and anaplerotic CO2 fixation. These findings imply that this bacterium could use their lithotrophic potential to gain additional energy from sulfur oxidation for both improving their growth and survival.

This thesis concludes that analyses in model organisms under defined growth conditions gives invaluable knowledge about the regulatory networks and physiological strategies that ensure the growth and survival of heterotrophic bacteria. This is critically important for interpreting bacterial responses to dynamic environmental changes.

Moreover, these analyses are crucial for understanding genetic and proteomic responses in microbial communities or uncultivated organisms in terms of defining ecological niches of planktonic bacteria

Place, publisher, year, edition, pages
Växjö: Linnaeus University Press, 2016. , 152 p.
Linnaeus University Dissertations, 245/2016Linnaeus University Dissertations
Keyword [en]
marine microbiology, physiology, heterotrophic bacteria, adaptive strategies, survival, proteomics, growth phase, proteorhodopsin, inorganic sulphur oxidation, anaplerotic CO2 fixation
National Category
Research subject
Natural Science, Environmental Science
URN: urn:nbn:se:lnu:diva-58257ISBN: 9789188357076 (print)OAI: diva2:1048832
Public defence
2016-05-20, Fullriggaren, Kalmar, 09:30 (English)
Available from: 2016-11-24 Created: 2016-11-22 Last updated: 2017-01-27Bibliographically approved
List of papers
1. Dynamics of metabolic activities and gene expression in the Roseobacter clade bacterium Phaeobacter sp. MED193 during growth with thiosulfate
Open this publication in new window or tab >>Dynamics of metabolic activities and gene expression in the Roseobacter clade bacterium Phaeobacter sp. MED193 during growth with thiosulfate
2014 (English)In: Applied and Environmental Microbiology, ISSN 0099-2240, E-ISSN 1098-5336, Vol. 80, no 22, 6933-6942 p.Article in journal (Refereed) Published
Abstract [en]

Metagenomic analyses of surface seawater reveal that genes for sulfur oxidation are widespread in bacterioplankton communities. However, little is known about the metabolic processes used to exploit the energy potentially gained from inorganic sulfur oxidation in oxic seawater. We therefore studied the sox gene system containing Roseobacter clade isolate Phaeobacter sp. strain MED193 in acetate minimal medium with and without thiosulfate. The addition of thiosulfate enhanced the bacterial growth yields up to 40% in this strain. Concomitantly, soxB and soxY gene expression increased about 8-fold with thiosulfate and remained 11-fold higher than that in controls through stationary phase. At stationary phase, thiosulfate stimulated protein synthesis and anaplerotic CO2 fixation rates up to 5- and 35-fold, respectively. Several genes involved in anaplerotic CO2 fixation (i.e., pyruvate carboxylase, propionyl coenzyme A [CoA], and crotonyl-CoA carboxylase) were highly expressed during active growth, coinciding with high CO2 fixation rates. The high expression of key genes in the ethylmalonyl-CoA pathway suggests that this is an important pathway for the utilization of two-carbon compounds in Phaeobacter sp. MED193. Overall, our findings imply that Roseobacter clade bacteria carrying sox genes can use their lithotrophic potential to gain additional energy from sulfur oxidation for both increasing their growth capacity and improving their long-term survival.

National Category
Research subject
Ecology, Microbiology
urn:nbn:se:lnu:diva-37307 (URN)10.1128/AEM.02038-14 (DOI)000344161700010 ()
Available from: 2014-09-27 Created: 2014-09-27 Last updated: 2017-01-27Bibliographically approved

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Muthusamy, Saraladevi
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