Bug of the Month: The Interesting Case of Filament Type 0803

Also in this month's microbiology spotlight, a new machine learning tool to analyze microscope images makes its debut

Bug of the Month: The Interesting Case of Filament Type 0803

Type 0914/0803 cropped from 1,000x differential interference contrast.

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Filament type 0803 has a unique backstory, and depending upon the reference source, has various potential associated growth causes. 

The manuals written by Glenn Daigger, Dr. Michael Richard and Dr. David Jenkins recognize type 0803 filaments as straight filaments extending from the floc surface or dispersed in bulk liquid ranging from 50-150 µm in length and approximately 0.8 µm by width with square cell shape, no attached growth and no visible sheath. Type 0803 was classified as a filament type correlated with conditions of high SRT and/or low F/M.

Having the honor to speak directly with Dr. Jenkins and Dr. Richard prior to their passing, I was interested to realize many years after their latest manual (written in 2004) that neither of them recognized this filament type anymore. Additionally, Eickelboom (who was active into the early 2000s) eventually no longer recognized type 0803 as an individual filament type, rather choosing to combine it with type 0914, which has similar morphological characteristics.

It is generally accepted that filamentous bacteria that grow dispersed in solution (part of type 0803s potential description) have higher kinetic growth rates, and therefore a filament type that most commonly grows dispersed would most likely contradict conditions such as high SRT and low F/M, in which bacteria with lesser metabolic needs and generally slower growth rates gain competitive advantage. Therefore, type 0803 slowly began to disappear from the list of filamentous bacteria morphotypes associated with low F/M, higher SRT values.

In some instances (such as Dr. Richard’s practice), type 0803 was dropped altogether, while in other practices, type 0803 is still recognized as type 0914/0803 morphotype.   

The Chloroflexi phylum

It is widely accepted that type 0914/0803 filament types are correlated with the Chloroflexi phylum. Chloroflexi phylum microbes are unique in that they are almost exclusively believed to be filamentous in nature. In general, Chloroflexi have slower kinetic growth rates than other filaments, and many Chloroflexi members also have the ability to store substrate (such as glucose) under anaerobic conditions for later consumption in aerobic zones of aeration basins. From a classification standpoint, type 0914/0803 is now most commonly recognized as a septicity/organic acid filament type. Based on a large database of split microscopy and DNA (16SrRNA sequencing), as well as various other sources (most notably Nelson and his lab’s studies), the Anaeroolinae class and Caldilineales, Anaerolineales, and Ardenticatenales order are all candidates (in some instances confirmed, and in other still in theory) for filament type 0914/0803 morphology.

Without going into great detail on the topic of microscopy/DNA correlations, a challenge in interpreting DNA results lies in the vast genetic diversity of Chloroflexi at lower taxonomic levels (such as the genus level). For example, significant correlation potential of filaments to DNA reads are commonly viewed at higher taxonomic levels, however, they have the potential to become diluted if only viewed at these lower taxonomic levels. Additionally, Chloroflexi often show a lower percentage of DNA reads compared to other microbes when observed under a microscope. This discrepancy is due to various complex and acknowledged factors. Consequently, DNA read percentages do not always reliably reflect the actual abundance of these microbes as seen through microscopy.

It is essential to consider the context of other findings within the sample prior to diagnosing type 0914/0803. As an example of this, it is useful to view other microbe morphotypes correlated with organic acids before feeling confident about type 0914/0803 diagnosis. This is especially important, because filament type 00675 (commonly referred to as type 0041/0675) looks similar to type 0803/0914, however it has a completely different correlated growth cause.

The operational control strategies for type 0914/0803 are similar to other septicity filament types and include “band-aid solutions” such as settling aids and RAS chlorination, as well as other strategies such as step feed configuration, optimization of selector zones, dilution of organic acid concentrations through increased RAS rates (or in some instances effluent recirculation), and reducing potential for organic acid formation to occur in various areas of the treatment plant.

Machine learning tool debuts

This link is a free resource for anyone to use. At this site, an image from your microscope may be uploaded and the API program reports the percentage of certainty it sees as a match. Please make sure to read the instructions as the API is designed to view one microbe or condition at

a time. Also, this is a first-generation version and while accurate enough to introduce it, it is still prone to confusion on occasion. 

I receive an email copy of any reports generated and can reach out if I see a discrepancy. Lastly, please note that one picture is most often not representative of a formal microscopic evaluation so this tool should only be used for microbes that people see under the scope and want to run by another source.

About the author: Ryan Hennessy is the principal scientist at Ryan Hennessy Wastewater MicrobiologyHe was trained and mentored by Dr. Michael Richard for over 10 years in wastewater microbiology, and serves as a microbiology services consultant. Hennessy is a licensed wastewater treatment and municipal waterworks operator in the state of Wisconsin and fills in as needed for operations at several facilities. He can be reached at ryan@rhwastewatermicrobiology.com. Hennessy's new book Wastewater Microbiology: Filamentous Bacteria Morphotype Identification Techniques, and Process Control Troubleshooting Strategies is now available on Amazon.


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