Explain what figure 1 shows, and how do the results support or refute the paper’

Question

Explain what figure 1 shows, and how do the results support or refute the paper’s main points.

nearly complete 16S rRNA gene was obtained from pure Results and discussion cultures using general bacterial primers 11F-1492R (Lane 1991). The 16S rRNA gene PCR products were purified Potential DR in sediments of hypersaline soda lakes from low-melting agarose using the Wizard PCR-Prep kit from Kulunda Steppe ga, USA). Sequencing was Dye Terminator v.3.1 sequencing reaction kit on an ABI The potential DR measurements in the sediment slurries 3730 DNA automatic sequencer (Applied Biosystems, amended with nitrogen oxides and electron donors revealed Inc.,USA). The sequences were aligned with those from highest N20 formation in a less productive lake with lac- GenBank using CLUSTALW. The 16S rRNA genetate as the electron donor (Fig. la), although nitrate sequences were first compared to sequences stored in the consumption was faster in the sediments from the other GenBank database using BLAST search tool. Phylogenetic two, highly productive, lakes. It is possible, that the acet trees were reconstructed with four different algorithms ylene block was not efficient in the latter, because of high using the TREECONW software package (van de Peer and sulfide concentrations in the sediments (Knowles 1990). At de Wachter 1994). Pair wise evolutionary distances least the potential for nitrite and N20 reduction was either (expressed as estimated changes per 100 nucleotides) were equal or even higher in the eutrophic lake sediments computed using Jukes and Cantor (1969) method. A (Fig. lb). The influence of pH and salt on the potential DR 1.60 1 C 1.40 ?Picturesque -Bitter-1 Tanatar-5 1.00 20 7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 Final pH values 1600 1 B Nitrate Nitrite N20 E 1400 ? 1200 1000 0.9 2.5 Picturesque Tanatar-5 Bitter-1 .2 0.7 1.2 72.2 2.7 3.2 3.74.2 Total Na, M Fig. 1 Potential denitrification activity in sediments of hypersaline reduction with 4 mM acetate in sediments freed from the pore waters soda lakes in Kulunda Steppe (Altai, Russia). a Potential nitrate and suspended in salt buffers. The solid lines depict N20 formation in (2 mM) reduction to N20 in natural sediment slurries with differen e presence of acetylene and the dashed lines depict nitrite electron donors (4 mM). b Reduction of different nitrogen oxides in formation; open circles lake Picturesque; closed circles lake Tana- the presence of 4 mM acetate in natural sediments. c, d Influence of tar-5; open triangles lake Bitter-1 pH (at 0.6 M total Na*) and soda (at pH 10), respectively, on nitrate

Explanation / Answer

Figure 1A is a graph that plots the potential DR in nmol of N2O produced when sediments from the lakes were supplemented with nitrogen oxide and an electron donor. This graph shows that the N2O production is highest in Picturesque lake when lactate was used as electron donor when compared to other lakes, although nitrate consumption was high in these lakes as well. The authors reason that the acetylene block was not efficient in the two other lakes due to presence of high sulphide concentrations because of whic high N2O production in these lakes was not observed.

Figure 1B is a graph that shows the rate of consumption of Nitrate, Nitriite and N2O in sediments from the three lakes in the presence of acetate. here the author mention that the potential for nitrate or N2O reduction is either equal or higher in the eutrophic lake sediments. However this is not evident from the graph. All three sediments consume nitrate and nitrates at different rates and is some lake N2O not consumed where as in sediment from lake Bitter-1, N2O is utilized. The statement made and data presented as evidence do not correlate.

Figure 1C presents data on the formation N2O and nitrites by lake sediments in the presence of acetate at different pH. The data shows that N2O formation happens in basic conditions and hence the author comment on the obligate alkaliphilic nature of N2O formation.

Figure 1D presents the data on the formation N2O and nitrites by lake sediments in the presence of acetate at different Na+ concentrations. Here they find that N2O formation is sensitive to Na+ concentrations. At low concetration of Na+, N2O formations is high and as Na+ concentration increases, N2O formation gradually decreases.

From Figure 1C adn 1D, the author also notice that at a certain threshold pH (10) and Na+ concentration (2.5 - M) the formation of N2O is not seen instead only formation of Nitriles is observed.

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