Microbial community structure & function inestuarine sediments
2013
Microorganisms are ubiquitous, abundant and hugely phylogenetically diverse, showing
a wide variety of metabolisms. The catabolic energy and carbon yielding activities of
microorganisms play important catalytic roles in biogeochemical cycles which are
ultimately fundamental to life on earth. Thus, understanding environmental microbial
diversity and how it relates to ecosystem function and how this may change with global
change, is a current major challenge of environmental microbiology. It is important to
understand microbial transformations in estuarine and coastal sediments because they
are key ecosystem components; being important sites for the mineralization of photic
zone biomass. Estuarine sediment from the mouth of the Colne estuary was sampled
and used to set up slurry microcosms for 16S rRNA archael and bacterial denaturing
gradient gel electrophoresis (DGGE) analysis. Geochemical activity measurements and
stable isotope probing experiments were carried out to investigate the response of
microbial community composition and diversity to phytodetritus (PD) loading and across
different redox phases typical of estuarine sediments. The addition of PD resulted in
significantly different bacterial communities while the archaeal communities were not
significantly different from the control. The increase in bacterial phylotypes was
dominated by fermenting Alteromonadales and the versatile Shewanella genus. Stable
isotope probing showed 13C-glucose utilization by Alteromonadales and Vibrio
confirmed stimulation of these fermenting groups in the dysaerobic phase. 13C acetate
incorporation by phylotypes similar to Firmicutes during the sulphate reduction phase
demonstrated how functional groups not previously found to be important at the
Brightlingsea site of the Colne estuary, may play an important role in anaerobic carbon
mineralization at this site. Thermoplasmatales and MBG-D like phylotypes incorporated
13C-acetate suggesting heterotrophic metabolism and the methylated compound
utilising Methanosarcinales and the predominantly H2/CO2 utilsing Methanomicrobiales
also incorporated 13C-acetate or its degradation products. This research demonstrates
how fermenting sedimentary estuarine microbial communities respond to organic
matter loading in estuarine sediments and the prevailing active and dominant groups in
the sulphate reduction phase.
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