Microbial diversity and functional response to the redox dynamics of pyrite-rich sediment and the impact of preload surcharge.

Microbial diversity and activities play pivotal biogeochemical roles in a redox-sensitive, pyrite-rich sediment's ecosystem. However, very little is known about the microbial community composition and distribution among the redox zones of pyrite-rich sediment and their response to changes caused by the burial of the sediment beneath compacted fill. In the present work, culture-independent, molecular phylogenetic investigations of the prokaryotic population and its diversity in a naturally occurring pyrite-rich sediment were undertaken to determine the microbial community composition, richness, diversity and distributions among the varying redox zones and their functional response to the imposition of surface surcharge, in the form of compacted fill. It was established that the pyrite-rich sediment is a redox-sensitive environment consisting of microhabitats with distinct and discontinuous physico-chemical characteristics, including DO, pH, Eh, temperature, electrical conductivity and salinity. It is a favourable environment for cyclic transformation of inorganic sulphur compounds and a unique environment for the habitation and growth of various microorganisms. Microbes adapted to the microhabitat and lived together in consortia, in response to their physiological and functional requirements. Microbes involved in the sulphur cycle had their populations concentrated in the oxic zone, while those involved in iron and carbon cycles were prevalent in the anoxic zones. As a result, highly diverse microbial populations occurred in isolated peaks within the sediment. The physico-chemical differences within the sediment changed in response to changes in the sediment redox dynamics. Imposition of the surcharge resulted in significant changes in the pH, temperature, Eh, DO, EC and salinity, reflecting marked re-distribution of the microbial population within the ecosystem. The cable bacteria phenomenon was evident in the sediment studied; however, there were doubt regarding their filamentous occurrence.