Ecological role of physiological and phylogenetic diversity in aquatic bacterial communities
Date
2010-12-13
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Abstract
Doktoritöös uuritakse looduslike veebakterite mitmekesisust ning ökoloogilist tähtsust Läänemeres, Barentsi meres ja Eesti väikejärvedes.
Veebakterite koosluse füsioloogilise ja liigilise struktuuri kujundavad mitmed keemilised, füüsikalised ja bioloogilised parameetrid ning nende koosmõjud. Peamiseks veebakterite aktiivsust mõjutavaks teguriks peetakse toiteainete kättesaadavust. Meie teadmised bakterite käitumisest toiteainete küllusest põhjustatud vetikaõitsengute ajal Läänemeres on paraku kesised. Doktoritöös uuriti katseliselt lämmastiku, fosfori ja süsiniku hulga muutuste mõju bakterikooslusele Läänemeres. Käsitletakse toiteainete kättesaadavuse mõju bakterite koosluse liigilisele struktuurile, aktiivsusele ning morfoloogiale.
Keskkonnatingimustest sõltuvalt muutub veebakterite aktiivsus pidevalt. Seetõttu sisaldub bakterikoosluses erineva aktiivsusega ja ka puhkavaid ning surnud rakke. Doktoritöö näitab, et veemikrobioloogias väga laialdaselt kasutusel olevate veebakterite arvukuse hindamise meetoditega arvestatakse bakterite üldarvu hulka ka paljud surnud bakterid. Tulemusena ülehinnatakse rakkude hulka, mis osalevad bakterite poolt veekogudes läbiviidavates protsessides ning alahinnatakse bakterite kasvukiiruseid. Kasutades arvutustes ainult aktiivsete rakkude arvukust on veebakterite kasvukiirused nii parasvöötmes kui ka polaaraladel sarnased laborikultuuridel mõõdetud kasvukiirustega. Saadud tulemused näitavad, et polaaralade bakterid on palju aktiivsemad, kui on näidatud varasemates uurimustes. Doktoritöös analüüsitakse toiteainete kättesaadavuse mõju aktiivsete bakterite sügavusjaotusele Barentsi meres ja Eesti väikejärvedes.
The current thesis shows the heterogeneity in aquatic bacterial world in different angles. The coastal Baltic Sea, Estonian stratified small lakes and the Arctic Barents Sea is used as model areas to describe bacterial heterogeneity and to find answers to several ecological questions. In marine and freshwater environment the complexity of factors that influence bacterial growth is difficult to follow. Optimizing growth rate at non-optimal nutrient levels must be an important aim for aquatic bacteria, given that marine and freshwater environments rarely offer growth-saturating concentration of nutrients. In the pelagic photic zone, nutrient limitation by e.g. phosphate, available nitrogen and degradable organic material, is believed to be a fundamental controlling factor for the community composition and activity of bacteria. Since eutrophication has become an increasing problem in marine coastal and estuarine areas, the question how heterotrophic bacteria respond to nutrient limitation is critical. In this study experimental approach was used to elucidate the effect of various combined additions of nitrogen, phosphorus and organic carbon to natural Baltic Sea bacterial community. Responses to changing environmental conditions enable single bacterial cell to drive in various physiological states as a part of their life strategy. Among the continuum of physiological states active and alive categories have the highest ecologically relevance as actual mediators of bacteria related processes. Accurate assessment of physiological status and proper estimation of environmental bacterial abundance excluding usually abundant dead cells has remained a difficult methodological problem up to date. As a consequence the scaling of growth, metabolism and uptake of organic substrates to total number of cells yield numbers that underestimate the real activity of processes. In this thesis the ecological relevance to determine physiological state of aquatic bacteria and to use only the number of living bacteria in cell-specific calculations is discussed. The effect of growth substrates on the distribution of active bacteria in the Barents Sea and Estonian lakes is analyzed.
The current thesis shows the heterogeneity in aquatic bacterial world in different angles. The coastal Baltic Sea, Estonian stratified small lakes and the Arctic Barents Sea is used as model areas to describe bacterial heterogeneity and to find answers to several ecological questions. In marine and freshwater environment the complexity of factors that influence bacterial growth is difficult to follow. Optimizing growth rate at non-optimal nutrient levels must be an important aim for aquatic bacteria, given that marine and freshwater environments rarely offer growth-saturating concentration of nutrients. In the pelagic photic zone, nutrient limitation by e.g. phosphate, available nitrogen and degradable organic material, is believed to be a fundamental controlling factor for the community composition and activity of bacteria. Since eutrophication has become an increasing problem in marine coastal and estuarine areas, the question how heterotrophic bacteria respond to nutrient limitation is critical. In this study experimental approach was used to elucidate the effect of various combined additions of nitrogen, phosphorus and organic carbon to natural Baltic Sea bacterial community. Responses to changing environmental conditions enable single bacterial cell to drive in various physiological states as a part of their life strategy. Among the continuum of physiological states active and alive categories have the highest ecologically relevance as actual mediators of bacteria related processes. Accurate assessment of physiological status and proper estimation of environmental bacterial abundance excluding usually abundant dead cells has remained a difficult methodological problem up to date. As a consequence the scaling of growth, metabolism and uptake of organic substrates to total number of cells yield numbers that underestimate the real activity of processes. In this thesis the ecological relevance to determine physiological state of aquatic bacteria and to use only the number of living bacteria in cell-specific calculations is discussed. The effect of growth substrates on the distribution of active bacteria in the Barents Sea and Estonian lakes is analyzed.
Description
Väitekirja elektrooniline versioon ei sisalda publikatsioone.
Keywords
dissertatsioonid, bioloogia, veebakterid, ökoloogiline roll, Läänemeri, Barentsi meri