Microbial Selection and Survival in Subseafloor Sediment

Area of Science:

• Marine microbiology
• Geomicrobiology
• Deep biosphere

Background:

• Subseafloor microbial communities are influenced by geochemical zones.
• Community succession and response to selective pressure with sediment depth remain underexplored.

Purpose of the Study:

• To investigate microbial community succession in subseafloor sediments.
• To understand the factors controlling microbial community composition at increasing sediment depths and ages.

Main Methods:

• 16S ribosomal DNA (rDNA) sequencing was employed.
• Microbial communities were analyzed in sediment cores from the Indian Ocean and Bering Sea.
• Sediment depths ranged from 0.16 to 332 meters below seafloor, with ages up to 1.3 million years.

Main Results:

• The majority of microbial taxonomic diversity was found in the shallowest sediments.
• Relative abundance in near-seafloor sediment best predicted sequence presence in older, deeper sediment.
• Dominant deep subsurface operational taxonomic units (OTUs) were subsets of the local surface community, not widespread specialists.
• Most abundant taxa decreased in relative frequency with increasing sediment depth and age.

Conclusions:

• Microbial community composition in deep, old subseafloor sediment is largely determined by the abundance of taxa present in shallower, younger sediment.
• The dominance of certain taxa in the deep biosphere may result from lower mortality rates rather than active replication.
• Community succession is driven by the preservation of near-surface communities over geological timescales.