Growth substrate limitation enhances anaerobic arsenic

Overview

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Key numbers

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• during the anoxic Archaean era, when MMAs(III) would have been chemically stable (18,
• Clostridial Broth (RCB), including 100%, 75%, 50%, or 25% RCB, in the presence and
• low growth-substrate media (50% and 25% RCB) (Fig. 1). More specifically, the growth
• its no-iAs(III) counterparts in the 100%, 75%, 50%, and 25% RCB, respectively (Fig. 1).
• detected at the beginning and end of incubation) (Table S1).
• FIG 1 Growth curves (optical density (OD600) (a) and total protein content (b)) of Paraclostridium bifermentans strain EML in anaerobic dilutions of RCB (100%,
• 75%, 50%, or 25% RCB) in the presence or absence of 25 µM iAs(III). Data are shown as mean values with error bars. Individual values for each biological triplicate
• Indeed, the normalized MMAs(III) concentration decreased in the following order: 25%
• RCB >50% RCB >75% RCB >100% RCB (Fig. 2). The greatest amount of protein-normal­
• ized MMAs(III) was produced by strain EML grown in the highest RCB dilution (25% RCB,
• 50%, 75%, and 100% RCB conditions, respectively (Fig. 2a). Similar patterns were also
• of MMAs(V) and DMAs(V) generated in the highest RCB dilution (25% RCB) (Fig. 2b and
• in 100% RCB and lowest in 25% RCB, suggesting a negative correlation between
• oxidation of trivalent As species by 10% (vol/vol) H2O2 (27–29). Oxidation is expected
• FIG 2 Time-dependent concentrations of protein-normalized aqueous As species in anaerobic RCB dilutions (100%, 75%, 50%, or 25% RCB) inoculated with
• values for each biological replicate can be found in Data Tables 2 and 19.
• expression stability of eight potential reference genes (Table S2) with the qBase plus
• FIG 3 (a) Transcripts of arsM gene of Paraclostridium bifermentans strain EML in anaerobic RCB dilutions (100%, 75%, 50%, or 25% RCB) in the presence and
• biological replicate are shown in Data Tables 3 and 20.
• highest number of arsM transcripts was detected in the most dilute medium (25%
• 12 times greater than in the treatments of 50% RCB +iAs(III) (2.63E + 04 copies/OD600),
• 75% RCB +iAs(III) (2.11E + 04 copies/OD600), and 100% RCB +iAs(III) (8.90E + 03 copies/
• statistical significance at P < 0.01. Individual values for each biological replicate are shown in Data Table 4.
• each biological replicate are shown in Data Tables 5 and 21.
• microorganisms (21). Because MMAs(III) and DMAs(III) are thermodynamically stable
• (100% RCB, 75% RCB, 50% RCB, and 25% RCB) (Supporting information Table S1). The
• medium was boiled for 5 min to remove O2, then cooled under a flow of 100% N2 gas
• with aluminum caps, and the headspace was flushed with 100% N2 to ensure anaerobic
• approximately 1% of the total volume (vol/vol). All bottles were incubated at 30°C in
• 1 mL of 1% HNO3 (≥69%, Honeywell Fluka). In addition, to analyze As species and total
• and stored overnight in a 1% HNO3 solution. For soluble intracellular As species, 1 mL
• 1% (vol/vol) bovine serum albumin (BSA) (Sigma). A 10-fold dilution series containing
• serum bottles containing 50 mL of 100% RCB medium, consisting of (i) strain EML + WT
• with the optimal ratio determined to be 10% EML (vol/vol), that is, the cell pellet from a

Methods (brief)

• products (7, 8). For instance, organic As (in particular dimethyl arsenate, DMAs(V)) is
• commonly detected in rice grains, along with inorganic As (9, 10). As DMAs(V) is much
• less toxic than arsenite, accumulation of DMAs(V) in rice grains largely reduces its toxicity
• to humans. However, there is evidence of a correlation between DMAs(V) accumulation
• (11, 12). In addition, because analyzing As in rice requires digestion, there is a concern
• and measured as DMAs(V) (13), unknowingly overlooking a potential threat to human
• acid (MMAs(III) and dimethylarsinous acid (DMAs(III)) are produced, they are rapidly
• thylarsonic acid (MMAs(V) and dimethylarsinic acid (DMAs(V)) (16). This paradigm is
• same resources. Although DMAs(III) might also function as an antibiotic under anaerobic
• 2a) or MMAs(V)/DMAs(V) concentration as a function of RCB dilution (Fig. 2b and c).
• observed for the oxidized samples, with the highest protein-normalized concentrations
• of MMAs(V) and DMAs(V) generated in the highest RCB dilution (25% RCB) (Fig. 2b and
• Paraclostridium bifermentans strain EML and 25 µM iAs(III). (a) MMAs(III) (no oxidation), (b) MMAs(V) (post-oxidation), and (c) DMAs(V) (post-oxidation). Individual
• retained by the HPLC column. If the samples are oxidized prior to measurement, the
• Thus, in oxidized samples, MMAs(V) corresponds to the sum of MMAs(III) and monome­
• microorganisms (21). Because MMAs(III) and DMAs(III) are thermodynamically stable
• S3). At selected time points and for each condition, triplicate bottles were sampled for
• MA, USA). For quantification of arsM gene expression, triplicate cultures were sampled

Implications

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Wiki pages this source may touch

• Fish — marine, predatory (tuna, swordfish, shark, king mackerel)
• Fish — marine, non-predatory (sardines, anchovies, salmon, cod)
• Arsenic
• Aluminum

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