Microbial community structure & function in estuarine sediments

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