Growth Effects of Rare Earth Metals on Methanogenic Archaea

Nick Havill Author

07/28/2021 Added

42 Plays

Description

Poster Presentation for UNL SRP 2021

Searchable Transcript

Search:

[0:00] Hello. My name is Nick Havill
[0:03] and today I’m going to be
[0:03] covering the research that I did as a part of the
[0:05] Bioenergy REU at the University of
[0:07] Nebraska-Lincoln 2021 summer research program.
[0:10] The Buan lab studies anaerobic archaea
[0:12] that produce methane, known as methanogens.
[0:14] These organisms are obligate anaerobes,
[0:17] meaning oxygen gas is toxic to them,
[0:19] so they live in environments like
[0:20] mammalian digestive tracts,
[0:21] ocean sediment, or acidic mud pots.
[0:24] The methane produced by methanogens
[0:26] makes up 2/3 of all biologically sourced methane,
[0:28] meaning that methanogens contribute
[0:30] significantly to greenhouse gas production.
[0:32] However, humans also harness methanogens
[0:34] in bioreactors to produce methane
[0:36] for energy, known as biogas.
[0:38] So, it’s really important that we understand
[0:40] what makes methanogens tick because
[0:42] they have this double effect on
[0:43] our climate and our energy sector.
[0:46] Some of the most important growth factors
[0:48] for methanogens are metal ions,
[0:50] which allow them to complete
[0:51] the chemical reactions that drive
[0:52] the methane cycle.
[0:54] Basically, this simplified graphic
[0:55] represents a reduction and oxidation cycle
[0:57] that involves a lot of electrons
[0:59] transferring between compounds.
[1:01] Methanogens use metal ions in their enzymes
[1:03] to serve as pathways for these electrons
[1:05] to move between atoms.
[1:07] Usually, these metals are things like
[1:09] iron, zinc, and copper, lighter metals
[1:11] that are pretty readily found
[1:12] in biological systems.
[1:15] However, let’s pivot for a moment
[1:17] and talk about the other organisms
[1:18] in this cycle.
[1:19] Methanotrophs are bacteria
[1:21] that perform the other side
[1:22] of this cycle, consuming methane
[1:24] and producing carbon dioxide.
[1:26] Methanotrophs basically perform the
[1:28] same reactions as methanogens
[1:29] in reverse, which means that
[1:30] their enzymes are very similar.
[1:32] Methanotrophs tend to use the same metal ions,
[1:35] but in the past 10 years
[1:36] there have been a few species discovered
[1:38] whose enzymes depend on using metals
[1:40] in the lanthanide series instead.
[1:42] The lanthanide series is a sequence
[1:43] of metals in the 6th row
[1:45] of the periodic table.
[1:46] They’re larger metals that are
[1:47] less common in nature,
[1:48] part of a group commonly
[1:50] referred to as the rare earth elements.
[1:52] They’re usually used in industry
[1:53] for things like specialized magnets
[1:55] and fluorescence, but this
[1:57] discovery that they were essential
[1:58] for the growth of methanotrophs
[1:59] showed us that they have
[2:00] biological significance as well.
[2:04] So, what we wanted to test
[2:05] in this project was
[2:06] whether lanthanides could also
[2:08] help methanogens grow.
[2:09] Specifically, since we know that
[2:10] many of the enzymes in methanogens
[2:12] are really similar to the
[2:13] enzymes in methanotrophs,
[2:14] could methanogens also grow better
[2:16] when exposed to lanthanides?
[2:18] And we also explored a few
[2:19] more specific questions like how
[2:21] different concentrations of lanthanides
[2:22] would affect methanogens
[2:24] and how different growing environments might
[2:25] allow them to take up lanthanides
[2:27] or prohibit them from doing so.
[2:29] Our methanogen of choice was
[2:30] Methanosarcina acetivorans,
[2:32] which is a methanogen species
[2:34] that’s capable of several different
[2:35] growth pathways and is pretty durable
[2:37] which makes it a good test subject.
[2:41] The first experiment we performed
[2:42] was to grow our methanogens
[2:44] in Balch tubes,
[2:44] which are specialized test tubes
[2:46] with an airtight seal.
[2:47] We prepared them in an anaerobic chamber
[2:49] with growth media that contains
[2:51] all the salts and nutrients that methanogens need
[2:53] as well as methanol,
[2:54] which is one of the carbon products
[2:55] that they metabolize into methane.
[2:57] As they grew, we measured
[2:59] the optical density of the tubes
[3:00] using a spectrophotometer,
[3:02] which told us the cell density
[3:03] in each tube.
[3:05] Over time, this creates a growth curve,
[3:06] which you can see here.
[3:07] This graph shows the
[3:08] natural log of optical density,
[3:10] which allows us to express
[3:11] the exponential growth of the
[3:12] cells in a linear fashion.
[3:14] This means we can make
[3:15] a best fit line that tells us
[3:16] the growth rate of the cells.
[3:18] From this, we can calculate
[3:19] the doubling time of the cells,
[3:20] which we can then
[3:21] compare to the control.
[3:24] We saw that many
[3:25] of the lanthanides
[3:26] result in a significantly
[3:27] faster doubling time.
[3:28] In this graph, we can see
[3:29] that with the grouping
[3:30] of steeper slopes.
[3:32] We can also look at this
[3:33] table and see the calculated
[3:34] doubling times in hours
[3:35] as well as the p-values
[3:36] of t-tests against
[3:37] the positive control.
[3:39] We saw several
[3:40] very low p-values,
[3:41] most notably with
[3:42] Gadolinium and Terbium,
[3:43] which increased growth rate
[3:45] by 41 and 31% respectively.
[3:47] We also saw that Praseodymium,
[3:49] the yellow line,
[3:50] it was pretty far from
[3:52] the other lanthanides
[3:53] and also much more variable.
[3:54] Praseodymium is the only
[3:56] lanthanide that we had to
[3:57] order as a
[3:57] non-stoichiometric hydrate,
[3:59] meaning that it doesn’t
[4:00] bind to water molecules
[4:01] in round numbers.
[4:02] This means that we
[4:03] couldn't accurately calculate
[4:04] its molecular weight,
[4:05] so we couldn't properly
[4:06] calculate the concentration
[4:07] we were adding to our
[4:08] Balch tubes.
[4:09] Additionally, we tried
[4:10] lyophilizing our
[4:11] praseodymium sample to
[4:12] minimize the effect of the
[4:13] unknown water weight,
[4:15] but this could have introduced
[4:15] error into the system
[4:16] where it wouldn't have existed
[4:17] in the other tubes.
[4:19] All of this means that
[4:20] we weren't totally confident in
[4:21] that specific result accurately
[4:23] representing the effect
[4:24] of Praseodymium on methanogens.
[4:27] In the second experiment,
[4:28] we decided to perform
[4:29] a dose-response curve
[4:30] for Praseodymium to
[4:31] get a benchmark for how
[4:32] increasing concentrations
[4:34] of lanthanides affect cells.
[4:35] We chose praseodymium
[4:37] because it was significant
[4:38] in the first round of experiments,
[4:39] but we also chose it because
[4:40] we wanted some more data
[4:41] to see if we saw something
[4:42] different without lyophilizing it.
[4:44] What we see in this first graph
[4:46] is the original growth curves
[4:47] for increasing concentrations
[4:48] of praseodymium,
[4:49] and we can see that
[4:50] the pink curve,
[4:51] which is the highest concentration,
[4:52] had a significant effect.
[4:54] The table shows the significance values
[4:56] of a t-test between
[4:57] the 0M positive control
[4:59] and each experimental concentration.
[5:01] We saw that the two
[5:02] highest concentrations were
[5:03] increasingly significant in
[5:04] lengthening the doubling time,
[5:06] meaning that higher concentrations
[5:07] of praseodymium were
[5:08] reaching a harmful level in the cells.
[5:11] This second graph shows
[5:12] that trend more clearly
[5:13] by graphing doublings per hour
[5:14] for each concentration,
[5:15] and we can see that
[5:16] there is a strongly correlated
[5:17] exponential curve that shows
[5:19] the decreasing growth rate.
[5:22] The final experiment we did
[5:24] was to grow methanogens
[5:25] with lanthanides in 96-well plates
[5:26] rather than Balch tubes.
[5:28] The main difference between
[5:29] these two environments
[5:30] is that a Balch tube
[5:31] has a constantly pressurized environment,
[5:32] while a plate is
[5:33] much more open to its surroundings.
[5:36] This creates a big difference
[5:37] in the carbon dioxide
[5:38] partial pressure,
[5:39] which is known to be
[5:40] an important consideration
[5:41] for methanogen growth.
[5:43] However, we could only
[5:44] read each plate once because
[5:45] we had to take them out
[5:46] of the anaerobic chamber
[5:47] to read them,
[5:48] which had the side effect
[5:49] of killing the cells.
[5:50] Because of this,
[5:51] we only took two timepoints
[5:52] at 5 and 11 days.
[5:55] We only saw
[5:55] a few significant differences
[5:57] between positive controls
[5:58] and experimental wells,
[5:59] but we also saw that
[6:00] some positive controls
[6:01] were not statistically overlapping
[6:03] with one another.
[6:04] This told us that there was
[6:05] too much inherent error
[6:06] in the system and that
[6:07] the plate results weren’t very reliable.
[6:11] The main result of our research
[6:12] is that Methanosarcina acetivorans
[6:14] grows faster in the presence
[6:15] of a number of
[6:16] different lanthanide metals.
[6:18] This is really exciting
[6:19] because it means that
[6:20] lanthanide metals can be used
[6:21] as a strong growth supplement
[6:22] for that species.
[6:23] This has huge implications
[6:25] for bioenergy because
[6:26] it means that biogas production
[6:28] can be significantly increased
[6:29] by introducing lanthanides
[6:30] into a bioreactor system.
[6:32] Future research is needed
[6:33] to test whether lanthanides
[6:35] can increase growth in
[6:36] other species of methanogens,
[6:37] but this result is encouraging
[6:38] given the metabolic similarity
[6:41] of methanogens as a class.
[6:42] Our praseodymium
[6:43] dose-response curve
[6:44] also reveals that
[6:45] lanthanides likely become
[6:46] toxic to methanogens
[6:48] in higher concentrations,
[6:49] which provides important
[6:50] context for finding
[6:51] the most effective dose
[6:52] for methanogen growth.
[6:54] In the future,
[6:54] running a dose-response curve
[6:56] for each of the
[6:56] other lanthanides
[6:57] will provide a complete
[6:58] dataset for this effect.
[7:01] We also want to perform
[7:02] growth curves in media
[7:03] that lacks some of the vitamins
[7:04] that help to maximize
[7:05] methanogen growth
[7:06] to see whether lanthanides
[7:07] can increase growth
[7:08] in a less favorable environment.
[7:10] Finally, we hypothesize that
[7:12] the valence electron configurations
[7:14] of the lanthanides
[7:15] may have something to do
[7:16] with which lanthanides
[7:17] are most effective,
[7:19] since valence electron transfer
[7:20] is the main mechanism
[7:21] of redox biochemistry.
[7:23] Future research could
[7:24] seek to isolate
[7:25] metabolic pathways
[7:26] that use specific metals
[7:27] and test whether
[7:28] certain lanthanides
[7:29] are more beneficial
[7:29] in these pathways
[7:30] to see if there is a correlation.
[7:33] This marks the end
[7:34] of my research presentation.
[7:35] These are my references
[7:36] and acknowledgements.
[7:37] Thank you for your time.

The screen size you are trying to search captions on is too small!

You can always jump over to MediaHub and check it out there.

Comments

0 Comments

Growth Effects of Rare Earth Metals on Methanogenic Archaea

Description

Searchable Transcript

Comments icon comment

Related Channels

Comments