Molecular Phylogenetic and Biogeochemical Studies of Sulfate-Reducing Bacteria in the Rhizosphere of Spartina alterniflora

Abstract

The population composition and biogeochemistry of sulfate-reducing bacteria (SRB) in the rhizosphere of the marsh grass Spartina alterniflora was investigated over two growing seasons by molecular probing, enumerations of culturable SRB, and measurements of SO4 2− reduction rates and geochemical parameters. SO4 2− reduction was rapid in marsh sediments with rates up to 3.5 μmol ml−1day−1. Rates increased greatly when plant growth began in April and decreased again when plants flowered in late July. Results with nucleic acid probes revealed that SRB rRNA accounted for up to 43% of the rRNA from members of the domain Bacteria in marsh sediments, with the highest percentages occurring in bacteria physically associated with root surfaces. The relative abundance (RA) of SRB rRNA in whole-sediment samples compared to that ofBacteria rRNA did not vary greatly throughout the year, despite large temporal changes in SO4 2−reduction activity. However, the RA of root-associated SRB did increase from <10 to >30% when plants were actively growing. rRNA from members of the family Desulfobacteriaceae comprised the majority of the SRB rRNA at 3 to 34% of Bacteria rRNA, with Desulfobulbus spp. accounting for 1 to 16%. The RA ofDesulfovibrio rRNA generally comprised from <1 to 3% of the Bacteria rRNA. The highestDesulfobacteriaceae RA in whole sediments was 26% and was found in the deepest sediment samples (6 to 8 cm). Culturable SRB abundance, determined by most-probable-number analyses, was high at >107 ml−1. Ethanol utilizers were most abundant, followed by acetate utilizers. The high numbers of culturable SRB and the high RA of SRB rRNA compared to that ofBacteria rRNA may be due to the release of SRB substrates in plant root exudates, creating a microbial food web that circumvents fermentation.

Molecular characterization of sulfate‐reducing bacteria in a New England salt marsh

“…This predominance of phylotypes within the Desulfobacteraceae family is consistent with molecular surveys of other salt marshes and cyanobacterial mats, that identified dominant phylotypes related to the genera Desulfonema , Desulfococcus and Desulfosarcina (Risatti et al ., 1994;Rooney-Varga et al ., 1997;Teske et al ., 1998;Hines et al ., 1999;Minz et al ., 1999;Klepac-Ceraj et al ., 2004). Most of the Plum Island sequences (Fig.…”

“…Different segments of the complex sulfate-reducing community can show different activity levels during different seasons. Quantitative rRNA hybridization experiments show seasonal activity patterns, in particular the increasing relative abundance of completely oxidizing SRB populations in the S. alterniflora rhizosphere during the early summer growth season, compared with total bacterial populations (Hines et al, 1999). The sequence data analysed in this study will provide a basis to design probes and primers to quantitatively assess the diverse range of sulfate reducers present in the environment.…”

“…Consistent with this working hypothesis, 16S rDNA phylotypes related to the nutritionally versatile, completely oxidizing genera Desulfonema , Desulfococcus and Desulfosarcina , were identified in the S. alterniflora rhizosphere of a New Hampshire salt marsh (Rooney-Varga et al ., 1997). According to oligonucleotide probe hybridization experiments of extracted community rRNA, these completely oxidizing SRB dominated the Spartina rhizosphere community (Hines et al ., 1999). In both cases, the relative abundance of completely oxidizing delta-proteobacterial SRB rRNA within the Spartina rhizosphere showed seasonal peaks that coincided with the early summer root growth periods of the S. alterniflora (Rooney-Varga et al ., 1997;Hines et al ., 1999).…”

“…According to oligonucleotide probe hybridization experiments of extracted community rRNA, these completely oxidizing SRB dominated the Spartina rhizosphere community (Hines et al ., 1999). In both cases, the relative abundance of completely oxidizing delta-proteobacterial SRB rRNA within the Spartina rhizosphere showed seasonal peaks that coincided with the early summer root growth periods of the S. alterniflora (Rooney-Varga et al ., 1997;Hines et al ., 1999). Fermenting bacteria degrade and transform complex organic compounds that that SRB can readily consume (Howarth, 1993).…”

Sulfate‐reducing bacteria in marine sediment (Aarhus Bay, Denmark): abundance and diversity related to geochemical zonation

“…The sulfate reducers are not only versatile in their metabolism but also in the environmental conditions under which they thrive (Muyzer and Stams, 2008), e.g. marine and freshwater sediments (Mußmann et al, 2005a;Leloup et al, 2006), hydrothermal vents (high temperature) (Dhillon et al, 2003), hypersaline microbial mats (Foti et al, 2007), acid mine drainages sites (extreme pH values), the rhizosphere of plants (Hines et al, 1999;Bahr et al, 2005) and the methane zone (no detectable sulfate) of marine sediment (Leloup et al, 2007). Thus, SRB present not only a large phylogenetic diversity but also a large range of habitats, including high and low sulfate concentrations.…”