Effects of hypoxia on the structure and function of microbial communities in surface marine sediments

Microorganisms play a pivotal role in regulating key ecosystem processes, particularly trophodynamics and biogeochemical cycles of carbon, nitrogen, phosphorus and sulfur. Increasing anthropogenic activities and the resulting eutrophication in the coastal areas have exacerbated both the occurrence and severity of hypoxia worldwide in the last two decades. Limited evidence has suggested that hypoxia can alter the oxidation-reduction balance and associated biogeochemical processes. Nevertheless, it is not known whether, and if so how, hypoxia can directly affect the structure and function of microbial communities in marine sediments, which regulate these biogeochemical processes. Our preliminary results of a 28-day microcosm experiment showed that the genetic profiles of microbial communities in marine sediments were different under hypoxic and normoxic conditions, suggesting that the structure of the sediment microbial communities could be dictated by hypoxia.

The structure of a microbial community may be altered by an environmental stress. Alternatively, the community may have no change in the structure (i.e. resistance), or show signs of changes but soon return to the original state (i.e. resilience). The resistance and resilience of microbial communities of marine sediments to hypoxia, albeit of obvious environmental importance, are largely unknown. Furthermore, changes in the structure of the microbial community may not necessarily lead to changes in the ecosystem functions, since the same function may be taken up by other species that survive the stress (i.e. functional redundancy). Surprisingly, it is not known whether, and if so to what extent, functional redundancy would occur in marine microbial communities under environmental stress, including hypoxia.

Capitalizing on the recent advancements in metagenomics and microarray-based genomic technologies for microbial community structure and function analysis, we propose the first systematic laboratory cum field study to:
1) study the effects of hypoxia on the structure of microbial communities in surface marine sediments;
2) investigate the subsequent effects of the altered microbial community composition on important biogeochemical processes involved in the carbon, nitrogen, phosphorus and sulfur cycles; and,
3) determine the resistance, resilience and level of functional redundancy in marine microbial communities.

Results of this hypothesis-driven study will, for the first time, provide the much needed quantitative assessment of the impacts of hypoxia on the microbial communities and the essential biogeochemical processes governing the global nutrient cycles. This is also the first scientific inquiry on the functional redundancy of marine microbial communities, which will provide important insight on the structure and function relationship of marine microbial communities.