ISMET terminology survey

As the number or researchers participating in the ISMET community grows and becomes inclusive of additional disciplines (e.g. bioelectronics and synthetic biology), it is important for the ISMET board to put forward recommendations on terminology that is preferred by the established community in order to communicate our science and strengthen the existing lexicon.

The International Society of Microbial Electrochemistry and Technology (ISMET) conducted a survey of the preferred terms used by researchers in the field of microbial electrochemistry and electromicrobiology. The survey considered terminology in four areas that included The Field, The Process, The Technology, and The Microorganisms. The principles for choosing terminology were, 1) A term needs to make scientific sense, thus the term needs to have a clear definition, 2) The term needs to be consistent with existing scientific terms from other fields such as microbiology or electrochemistry, 3) The number of different terms should be limited to the strictly necessary.

The survey was distributed to over 300 researchers that are actively involved in ISMET and receive the ISMET newsletter, are ISMET members, or have been to an ISMET meeting in the last year. 231 responses were recorded for each question, demonstrating a >75% response rate for the survey. Respondents represented students, postdoc, early career and established researchers in ISMET. A summary of the results were presented at the ISMET7 meeting in Okinawa and are given below. Also provided are representative comments regarding each question. We recognize that the use of specific terms to define an individuals’ research is important and that terms are only useful if they are adopted by a field. Therefore, the results of this survey are not meant to be prescriptive but can serve as a reference point for those in the ISMET community.

Part I: The Field

The category “Other” included primarily Microbial Electrochemical Technology

Representative comments on the Field:

  • Electrobiotechnology is indeed another valid term that possibly better describe electrode-driven biotechnologies, while Microbial Electrochemistry is perhaps more suitable to indicate fundamental aspects.”
  • I don’t like the terms “Electrobiotechnology” and “Bioelectrochemistry” because these terms also involve enzymatic electrochemistry (which is not related to ISMET).”
  • “I do not think any of the above is incorrect, but the society is ISMET, so we have indirectly chosen ME as the field term. Bioelectrochemistry is a VERY general term that is used in enzymatic and medical electrochemistry. I would think we need a more specific term than that.”
  • “To me, microbial electrochemistry suggests electrochemistry with whole cells. Bioelectrochemistry would be wider term including systems using only enzymes. Electromicrobiology emphasizes the microbiology, e.g. electron transfer through and between cells, and does not necessarily relate to interactions between electrodes and cells.”
  • “I think that fundamental and applied research can be associated with the term “microbial electrochemistry” and correspond to the organization of ISMET. If we wanted to highlight the research on technology (MFC, MES,…), I would prefer the term “Electromicrobial technology”.”

Part II: The Process

The category “Other” in the second question included primarily Bioelectrochemical Technology

Representative comments on the Process

  • The term “Extracellular electron transfer” is already used by everyone and I don’t see any problem linked to it. I don’t see what other information is given by the other terms.”
  • “Since the transport out of the cell implies that electrons will be disconnected from the cells and connected to another material, I prefer transfer over transport. Transport is more suitable for processes inside a system, e.g. a cell or may be even biofilm. But I would draw the border latest at the electrode surface.”
  • “I reserve electron transfer for the singular passing of one (or a few at a time) electron from one carrier to another. I use transport to refer to the aggregate effect of multiple transfers e.g. from a cell through a network of carriers to an electrode.”
  • I think you can only use catalysis if you know for sure the interaction on the electrode is being catalyzed and not biologically transformed/incorporated to the cells metabolism. We wouldn’t call respiration catalysis. I think we often don’t investigate this thoroughly so we should be careful about general use.”
  • “If you are referring to electron transfer to/from an electrode, this is not catalysis. If there is a chemical reaction being accelerated by the electrons donated/accepted by the cell, then this is just an extracellular catalytic reaction, but I’m not sure we need a new name for it. Extracellular hydrogenases, cellulosomes, etc… are called just that.”

Part III: The Technology

Representative comments on the Technology

  • “BES provides the broadest coverage. Bioelectrochemical cell would also fit, whenever the reactor is really a single cell.”
  • “The problem is that “BES” is already largely used in the community, but this name is very confusing (it is used only for microbes, while e.g. protein electrochemistry exists for much longer time and commonly use the prefix “bio” for multiple occurrences e.g. biofuel cell)”
  •  “Device name should match field name — BES with bioelectrochemistry, or MES with microbial electrochemistry. MES and MEC get confused by additional common use of these acronyms for microbial electrolysis cell and microbial electrosynthesis. same with MET — if the field is microbial electrochemistry — MET makes sense. if bioelectrochemistry..probably BET”
  • I try to stay away from the bio-terms. Our systems are all microbial and the specificity is important to distinguish us from other fields.”

Part IV: The Microorganisms

How do you define the term “electroactive microorganism”?

  • “Microorganisms able to give or take electrons from/to electrode (or minerals) by themselves without the help of an external molecules (produced by other microorganisms, by an electrochemical reaction or just added to the medium)”
  • “Able to produce a measurable current in the absence of exogenous mediators. So self-produced mediators are OK.”
  • “A microorganism that either generates or consumes current by direct contact.”
  • “An electroactive microorganism must interact with an electrode in a physiologically meaningful way, i.e., there must be a detectable change in growth and/or metabolism caused by electron transfer between the microbe and electrode.”
  • “Organism that uses electron transfer for respiration.”
  • “An electroactive microorganims is capable to exchange electrons with an electrode.”
  • “An organism capable of performing extracellular electron transfer to a mineral or electrode”
  • “Having electrochemical activity.”
  • “I don’t use this term. What does it mean? All microorganisms actively use electrons. Does this only refer to an electrode?”
  • “Big question! Which processes do we include in that definition, let’s list them: 1) Microorganisms able to exchange electrons with a conductive material when in contact with its surface (so-called “direct electron transfer”). Necessarily included as electroactive (one could still wondered if we should suggest a minimum threshold in current per bacterium to consider it electroactive…) 2) Microorganisms able to exchange electrons with a conductive material via self-generated dissolved redox mediator (e.g. for Pseudomonas with phenazines).”
  • “Actually I want to see another term here: “electrochemically active microorganisms”. I think that term is better than “electroactive microorganism” (what does “electroactive” mean?)”
  • “All microorganisms are electroactive, the term is inadequate for ISMET”
  • “The terms anodotroph/electrotroph is etymologically incorrect! Troph comes from the term to feed (or food), which is the electron donor.”
  • “*phile does not mean the organism can actually use electron transfer in any way, just that it likes to be where it happens. Alkalophiles do not eat/create base, they just like to be in alkaline conditions. *gen means they produce something, but electricigen would mean they produce electricity, which in itself is not true, or would incorporate anodic and cathodic processes, because electricity is just flow of electrons no matter which direction. I think, Exoelectrogen for microbes transferring electrons to a solid electron acceptor outside the cell and Exoelectrotroph for organisms accepting electrons from a solid material outside the cell.”
  • “Every single microbial cell must be shuttling electrons to final electron accepter, however we only consider the electroactive microbes as those shuttles significant number of electrons,which we can measurable. The range of electrons per second or something else which we should mention in the definition.”
  • “I don’t think it should include the suffix phile, as that implies preferred growth, and I think electricigen is too human-centric.”
  • “In terms of a troph classification EAM are chemoheterotrophs. The classication of a single species in anodophile/cathodephile can be made e.g. based on the value of alpha_a or alpha_c in the Butler-Volmer-Equation, i.e. using 1 = alpha_a + alpha_c so alpha_a > 0.5 = anodophile or alpha_a < 0.5 = cathodophile.”
  • “I think that the way some people use electricigen vs. electrotroph bothers me the most. Anything that causes electrons to move is generating a current of some sort and thus could be considered an electricigen. Electrotroph is a decent term for an organism generating cathodic current if, and only if, that current is used to supply the energetic needs of the cell, e.g. secreted enzymes that generate current by catalyzing a reaction that has no effect on the cells does not count. Anodotroph is just wrong, because an anode is serving as an electron acceptor, not as the supply of electrons the way that chemo- or phototrophs use their namesakes to supply energy. the -philes suggest an enrichment at those electrodes, but could also apply to bacteria that grow there for secondary or tertiary reasons, e.g. they like the microoxic conditions produced at the cathode. Anode respiring bacteria is exclusionary, and I thought we were trying to have a big tent here.”

Part V: Bonus Questions