Skip to main content

Journal Club:”Direct Exchange of Electrons Within Aggregates of an Evolved Syntrophic Coculture of Anaerobic Bacteria” - OR: How Bacteria Hook up to Share Energy

Another curious observation made the science rounds the past week: wired, electric bacteria. Reading this article reminded me of a review article on dissimilatory bacteria I read before, and one of the most interesting talks I ever attended in my life titled "Eavesdropping on Bacterial Conversations".

What did they do?

Figure 1. Conceptual diagram showing electric symbiotic
relationship between G. metallieducens and G. sulfurreducens.

Summers, who is Microbiologist working in the Lovley lab at the University of Massachusetts, was studying Fe(III) reducing bacteria in the soil. They wondered what would happen when Fe(III) reducing bacteria would deplete Fe(III) available in the soil. In order to study this question, the research group co-cultured two strains of geobacter bacteria: Geobacter metallireducens and Geobacter sulfurreducens. The research team thought that combining the former bacteria that can oxidize ethanol in order to obtain energy, but normally must pass obtained electrons onto Fe(III) which was not present in the solution, with the latter strain which cannot metabolize, but can reduce fumerate to succinate while consuming hydrogen released by the previous bacterial species, would lead to the formation of an electrical symbiosis. The effect where one bacteria lives off the products of another bacteria is called syntrophy, and the authors wondered how this might happen.

They hypothesized that together these two bacteria could metabolize ethanol completely. In order to select for those bacteria that were capable of doing so, nine co-cultures were grown together and sequentially transferred when each co-culture was able to metabolize at least 70% of the supplied ethanol.

After a few months, they observed red bacterial aggregates forming. The role of interspecies hydrogen transfer has been debated in the field. The group wanted to study importance of this function within these aggregates and therefore knocked out a gene required to make hydrogenase. To their surprise, knocking out hydrogenase function did not have any effects on ethanol metabolism efficiency, but it sped up the formation of the aggregates (21 days instead of 7 months). This observation suggested that alternative mechanisms for electron transfer must other than interspecies hydrogen transport.

Upon sequencing the genomes of the co-cultured bacteria, a single mutation in G. sulfurreducens encoding an enhancer binding protein gene was found. Expressing this mutation in wild type strains also reduced aggregate formation time down to 21 days suggesting that this mutation is sufficient to promote aggregate formation.

The mutation lead to increased expression of various targets amongst which is a pili-associated cytochrome c-type protein which normally promotes electron transfer to Fe(III) oxides. Knocking out the gene inhibited growth of the bacteria even after more than nine months. Thus, this observation strongly suggests that G. metallireducens is passing its electrons directly to G. sulfurreducens without a hydrogen intermediate, giving us a concrete example for a sort of electric symbiosis.

Why is this significant?

According to Ken Nealson, who was asked about this research by The New Scientist, there are potential far reaching implications of this kind of symbiosis for disease treatment and diagnosis. Professor Nealson also wondered if human cells in our body are wired like these bacteria. On a personal note, I also see potential applications for the environmental and/or sustainable biotechnology field.

In our next journal club we will look at an article analyzing the microbial community inside cow stomachs.

As usual, I encourage everyone to read the original article which can be obtained from here:

Popular posts from this blog

Sustainable Living: Sunscreens

This is an important topic and so I want to get the most important things out of the way first:

Chemical sunscreens containing the following ingredients contribute to coral bleaching: 
OxybenzoneOctinoxateOctocrylene (used to also stabilize avobenzone)4-methylbenzylidine camphorAnything containing Parabens Don't be part of the problem and avoid using them! It's important to note that claims on sunscreens are not regulated and therefore, companies can put the wording "coral reef safe" on the packaging even though they contain the above chemicals. This is misleading if not outright false. Instead use "physical" sun screens that contain non-nanoparticle zink oxide. Physical sun screens differ from chemical sunscreens in that the sit ontop of the skin to reflect or scatter UVA/B rays away from the skin before it reaches it. Chemical sunscreens absorb the UVA/B rays instead to neutralize them.

To be clear, I am not proposing not using sunscreen! Instead use phys…

Focus on Algae - Part II: Energy

In the last focus section, we discussed how algae can be used to treat waste waters and mitigate CO2 in the process. Today's post will explore how algae can be used for energy generation. As already mentioned in the last time, biofuels have become very visible as of late due to environmental, economical and geopolitcal reasons. If at the heart of traditional biofuel generation lies in the creation and decomposition of biomass, then it would be easy to substitute corn or other less controversial land-based plants with algae. Although a lot of attention is paid to the use of algae in biofuel generation, and this article also mainly focusses on this aspect, it should be noted that algae can also be used to generate electricity by direct combustion of the biomass. Plans for these kinds of schemes are already on the way in Venice and a few other European locations [1].

Algae and Biofuels

What happens to the biomass after it has been created depends on the type of biofuel that is desired…

Sustainable Living: One man's trash...

Since Earth Week is starting tomorrow, I wanted share with you some concrete ways of how individuals like you and me can make an impact on a wider scale. I then also wanted to use this example to challenge everyone to think creatively about the larger context.

So you know how the saying goes: "One man's trash is another one's treasure." Today, I want to talk to you about garbage. Plastic garbage specifically. Plastic is quite a wondrous material. Made from oil by man with just a few additives can turn this polymer into so many different sorts of plastics with so many different properties from thin and flimsy plastic bags, to the carpet on which I am standing, to this plastic bottle from which I am drinking.