Community Interaction Co-limitation: Nutrient Limitation in a Marine Microbial Community Context.

The simultaneous limitation of productivity by two or more nutrients, commonly referred to as nutrient co-limitation, affects microbial communities throughout the marine environment and is of profound importance because of its impacts on various biogeochemical cycles. Multiple types of co-limitation have been described, enabling distinctions based on the hypothesized mechanisms of co-limitation at a biochemical level. These definitions usually pertain to individuals and do not explicitly, or even implicitly, consider complex ecological dynamics found within a microbial community.

Nutrient co-limitation at the boundary of an oceanic gyre.

Nutrient limitation of oceanic primary production exerts a fundamental control on marine food webs and the flux of carbon into the deep ocean. The extensive boundaries of the oligotrophic sub-tropical gyres collectively define the most extreme transition in ocean productivity, but little is known about nutrient limitation in these zones. Here we present the results of full-factorial nutrient amendment experiments conducted at the eastern boundary of the South Atlantic gyre.

Automated preconcentration of Fe, Zn, Cu, Ni, Cd, Pb, Co, and Mn in seawater with analysis using high-resolution sector field inductively-coupled plasma mass spectrometry.

A rapid, automated, high-throughput analytical method capable of simultaneous analysis of multiple elements at trace and ultratrace levels is required to investigate the biogeochemical cycle of trace metals in the ocean. Here we present an analytical approach which uses a commercially available automated preconcentration device (SeaFAST) with accurate volume loading and in-line pH buffering of the sample prior to loading onto a chelating resin (WAKO) and subsequent simultaneous analysis of iron (Fe), zinc (Zn), copper (Cu), nickel (Ni), cadmium (Cd), lead (Pb), cobalt (Co) and manganese (Mn) by high-resolution inductively-coupled plasma mass spectrometry (HR-ICP-MS). Quantification of sample concentration was undertaken using isotope dilution for Fe, Zn, Cu, Ni, Cd and Pb, and standard addition for Co and Mn.

Hydrogen peroxide in deep waters from the Mediterranean Sea, South Atlantic and South Pacific Oceans.

Hydrogen peroxide (HO) is present ubiquitously in marine surface waters where it is a reactive intermediate in the cycling of many trace elements. Photochemical processes are considered the dominant natural HO source, yet cannot explain nanomolar HO concentrations below the photic zone. Here, we determined the concentration of HO in full depth profiles across three ocean basins (Mediterranean Sea, South Atlantic and South Pacific Oceans).

Substrate hydrophobicity and cell composition influence the extent of rate limitation and masking of isotope fractionation during microbial reductive dehalogenation of chlorinated ethenes.

This study investigated the effect of intracellular microscale mass transfer on microbial carbon isotope fractionation of tetrachloroethene (PCE) and trichloroethene (TCE). Significantly stronger isotope fractionation was observed for crude extracts vs intact cells of Sulfurospirillum multivorans, Geobacter lovleyi, Desulfuromonas michiganensis, Desulfitobacterium hafniense strain PCE-S, and Dehalobacter restrictus. Furthermore, carbon stable isotope fractionation was stronger for microorganisms with a Gram-positive cell envelope compared to those with a Gram-negative cell envelope.

Degradation of chlorotriazine pesticides by sulfate radicals and the influence of organic matter.

Atrazine, propazine, and terbuthylazine are chlorotriazine herbicides that have been frequently used in agriculture and thus are potential drinking water contaminants. Hydroxyl radicals produced by advanced oxidation processes can degrade these persistent compounds. These herbicides are also very reactive with sulfate radicals (2.