Dissolved prokaryotes

Finally, we must somehow resolve the vexing problem of the chemical speciation of trace elements in seawater what is the chemical nature of the various metal chelators whose existence has been demonstrated by electrochemistry Is the chemistry of several metals in surface seawater really controlled by metallophores released by prokaryotes Or are dissolved metals chiefly present as parts of metalloproteins in the process of remineralization How do metal chelators affect the residence times of metals (in particular, scavenged elements such as iron and cobalt) and in turn how do those chelators influence the global carbon cycle via changes in marine primary productivity ... 

Microbial mats are communities in surface water ecosystems where bacteria and bacterial processes dominate. In microbial mats dissolved nutrients and metabolites are transformed by one-dimensional (vertical) molecular diffusion. The distinction between microbial mats and biofilms is not sharp. By definition (Fenchel et al, 1998), microbial mats are typically stratified vertically with respect to different functional types of bacteria. Microbial mats are thicker (often several millimeters) than biofilms. In microbial mats various types of filamentous prokaryotes are the most conspicuous part and they are responsible for the mechanical coherence of the mat. The mechanical stability of microbial mats is reinforced by the bacterial excretion of mucous polymers, producing a gelatinous matrix. 

Other plausible candidates for the first prokaryotes are the ancestors of chemotrophes colonizing hydrothermal vents. Today they use the oxygen dissolved in ocean water to obtain energy from the sulphides emanating from the hot springs in chemosynthetic reactions (see Box 1.10) that can be summarized by ... 

Siliceous diatoms are single-ceUed prokaryotes, about 100 pm in diameter, enclosed by a porous silica shell, in the form of two overlapping dishes, like a petri dish. The organism multiplies by dividing into two disc-shaped cells and then forming two new dishes back-to-back. The cells then separate, each with one new half shell and one old one. Recent work on the proteins involved in silica mineralization has started to clarify the details of silica deposition in diatoms and sponges. Plants often contain silica as a reinforcing material, and the structure of bamboo has been much studied in this context. Seawater and soil water contain low levels of dissolved silica as silicic acid, which the cell probably binds and transports as a complex with catechols (dihydroxybenzene) and then converts this to silica nanoparticles. 

Nature demonstrated the use of regular 2dimensional protein grids in bacterial surface S-layers (5 nm to 15 nm thick). These layers are protein crystals forming the outermost cell envelope of many prokaryotes. A variety of lattice symmetries from pi, p2, p3, p4 to p6 is found in bacterial strains. Sometimes even a single strain is able to switch from one type of S-layer to another induced via a change in the microenvironment. The pores and spacing in between the units varies from 3-30 nm. S-layer proteins are handled dissolved or suspended in a buffer at a concentration of up to 2 mg/ml. Their stability and unique property to coat two-dimensional arrays with perfect uniformity makes them an ideal nano-template. 

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