No Smoking : Bacterial Diversity and Ecosystem Succession on Inactive Deep-Sea Vents.

For decades marine microbiologists have surveyed active deep sea vents for microbial diversity and much data has been collated on the microbiology in these hot, sulphide venting environments. However, little work has been done in the area of inactive vents where sulphides remain in massive deposits below the seafloor. Previous studies clearly showed that the microbial communities of active and inactive hydrothermal vents are distinct using 16S rRNA clone libraries. The authors of this study aimed to take a much deeper view of the microbial diversity of inactive vents to learn their bacterial diversity, the metabolic potential and the succession between venting and non-venting communities.

Samples were taken from different sections of inactive vents on a fast-spreading ridge in the East Pacific Rise (EPR). DNA was extracted from the samples and analysed using more advanced sequencing techniques than used previously, such as pyrosequencing. All samples taken from the inactive vents showed communities of alpha-, beta-, delta-, and gammaproteobacteria and Bacteroidetes spp. which were the most predominant species present. As many as 26% of the V6 tags (sequence products) produced were found to be similar to sequences found in bacterial communities involved in sulphur, nitrogen, iron, and methane cycling on active vents. Epsilonproteobacteria that are highly abundant in active vent environment have been shown through the authors' results to account for less than 4% of the V6 tags found in the inactive vent samples. Also Aquificae spp. that are common in venting sites were shown to be completely absent in inactive venting sites using both V6 tag and full-length 16S rRNA methods. Both molecular methods showed greater proportions of alpha and betaproteobacteria and Bacteroidetes spp. compared to communities on active hydrothermal sites. Many of these species are suspected to have abilities to reduce transformations of Sulphur, Nitrogen and Iron. This is because, following the inactivation of a vent, the microbial community has to shift from using energy transferred from sources such as heat from the vent to having to convert energy chemically when the vent becomes inactive. These new chemolithoautotrophic species then provide organic carbon that would not be present due to the inactivity of the vent which can be utilised by other bacterial species to encourage the formation of a complex microbial ecosystem. The loss of heat through the inactivation of the vents also provide an opportunity for these chemolithoautotrophs to colonise the different minerals inside the chimneys that would not ordinarily be available whilst active again aiding the formation of the succeeding community.

The authors also look to further research to identify the different succession patterns with respect to thermophilic Archaea being present when the vent is active and any switch to mesophiles (those that grow at moderate temperature or psychrophiles (those that grow at extreme low temperatures).

A review of : Sylvan JB, Toner BM, Edwards KJ. 2012. Life and death of deep-sea vents: bacterial diversity and ecosystem succession on inactive hydrothermal sulfides. mBio 3(1):e00279-11. doi:10.1128/mBio.00279-11.