Possible abortive or defective encystment in Brachonella contorta-like species (3) in a freshwater coastal pond

William Bourland considered this to be a "Brachonella contorta-like species" when I shared images with him (3). From his paper (1), this organsim seems to conform to B. contorta with some obvious characters: notably the shape of the preoral dome is conical and the shape of the posterior end is truncate obconical (1). Note that the captioned pictures are from an individual trapped and compressed under the coverslip. It is most interesting that some of my B. contorta-like individuals had a posterior granular aggregate in addition to the characteristic anterior granbular aggregate. This has not been observed before according to William Bourland (3).

This Brachonella contorta-like species was the most common metopid in my 1 1/2 week old sample from the freshwater coastal Ocean Dunes pond situated in the Atlantic Double Dunes reserve.
I observed a peculiar behavior of B. contorta in my samples, a process of abortive encystment. Bourland et al 2018 describe the earliest stages of this process in Brachonella pulchra. "Extrusomes (mucocysts) are ejected in the first stages of encystment. The ejected extrusomes then undergo a rather striking transformation to thickened ropy structures forming a dense meshwork of nodular filaments" (1).

What I am seeing seems to conform to this wherein the ciliate stops swimming and forms a mucilagenous membrane around its body in which it begins to rotate for varying periods of time, so far for up to 10 minutes. But rather than completing the encystment process, the ciliate squeezes through a defect in this mucilagenous membrane and swims off, sometimes remaining viable and other times dying soon after. You can see this in the sequence of pictures of this abortive encystment.

This seems similar to the experience of Bourland et al 2018 to artificially induce encystment. "Although Brachonella pulchra thrived in autoclaved (i.e. deoxygenated) culture medium in closed Falcon tubes, attempts to induce encystment by isolating starved cells under a supported coverglass at atmospheric oxygen concentrations failed. Under these conditions, starved cells became distressed and ejected their extrusomes to form a rather disorganized mucus envelope but then died without completing cyst formation. When such preparations were placed in an anaerobic environment, cells encysted completely. This suggests that the process of encystment might be particularly sensitive to oxygen tension. Although we lack a comprehensive understanding of factors inducing encystation in metopids, they probably include those established in other ciliate lineages such as colpodeans and hymenostomes (e.g. starvation or other adverse environmental factors). Given the anaerobic/microaerophilic lifestyle of metopids, elevated oxygen tension may be an additional adverse environmental factor inducing encystation. However, it is possible that, if the oxygen level rises too high or too rapidly, encystation may be hampered" (1).

"Nutritional deficiency is a dominant factor in inducing cyst formation. Not only general food insufficiency can induce cyst formation, lack of specific food source, such as vitamins, can also lead to encystment.
Other conditions, including unfavorable changes in temperature, freezing, humidity, salinity, ultraviolet irradiation, dehydration, and population density have also been reported to be involved in inducing encystment. Additionally, change in pH, concentration of Ca2+ or K+ and oxygen may induce cyst formation in some species as well" (2).

Imaging in Nomarski DIC using Olympus BH2 under SPlan 40x objective plus variable phone cropping on Samsung Galaxy S9+

1. https://www.microbiologyresearch.org/content/journal/ijsem/10.1099/ijsem.0.002888
   Morphologic and molecular characterization of Brachonella pulchra (Kahl, 1927) comb. nov. (Armophorea, Ciliophora) with comments on cyst structure and formation. William Bourland, Johana Rotterová, Ivan Čepička. Int J Syst Evol Microbiol 2018;68:3052–3065