Key respiratory genes elucidate bacterial community respiration in a seasonally anoxic estuary

Abstract

Intense annual spring phytoplankton blooms and thermohaline stratification lead to anoxia in Chesapeake Bay bottom waters. Once oxygen becomes depleted in the system, microbial communities use energetically favourable alternative electron acceptors for respiration. The extent to which changes in respiration are reflected in community gene expression have only recently been investigated. Metatranscriptomes prepared from near-bottom water plankton over a 4-month time series in central Chesapeake Bay demonstrated changes consistent with terminal electron acceptor availability. The frequency of respiration-related genes in metatranscriptomes was examined by BLASTx against curated databases of genes intimately and exclusively involved in specific electron acceptor utilization pathways. The relative expression of genes involved in denitrification and dissimilatory nitrate reduction to ammonium were coincident with changes in nitrate, nitrite and ammonium concentrations. Dissimilatory iron and manganese reduction transcript ratios increase during anoxic conditions and corresponded with the highest soluble reactive phosphate and manganese concentrations. The sulfide concentration peaked in late July and early August and also matched dissimilatory sulfate reduction transcript ratios. We show that rather than abrupt transitions between terminal electron acceptors, there is substantial overlap in time and space of these various anaerobic respiratory processes in Chesapeake Bay.

Nitrogen and oxygen availabilities control water column nitrous oxide production during seasonal anoxia in the Chesapeake Bay

“…This pattern is consistent with a metatranscriptome analysis that showed lowest transcript ratios for denitrification in June before the onset of hypoxia and highest ratios in August when anoxia was most pronounced (Eggleston et al, 2015 Denitrification, as a major pathway of fixed nitrogen removal, is critical to mitigating eutrophication in natural waters.…”

Denitrifying community in coastal sediments performs aerobic and anaerobic respiration simultaneously

“…This contrasts with other environmental studies, where switches in expression of low-and high-affinity terminal oxidases have been observed over oxic-anoxic gradients. However, in other studies, the changes in O 2 concentration occurred at time scales of weeks, or over spatial scales of meters (Schunck et al, 2013;Hewson et al, 2014;Eggleston et al, 2015;Kalvelage et al, 2015). In permeable sediments, changes in O 2 concentration happen over minutes and hours and at spatial scales of millimeters to centimeters.…”

Ecological Energetic Perspectives on Responses of Nitrogen-Transforming Chemolithoautotrophic Microbiota to Changes in the Marine Environment

“…In stark contrast to higher organisms such as plants and animals, bacteria and archaea employ diverse and complex energy metabolic pathways (Kolber, 2007), which are adapted to and effective in diverse environments. Microbial communities select energetically favorable electron donors and acceptors from their environment for energy transduction (Bar-Even et al, 2012; Eggleston et al, 2015). Even so, energy may be a limited resource for certain marine ecosystems (Burgin et al, 2011; Moore et al, 2013; Vallino and Algar, 2016).…”