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A long (microbial) journey…

Posted by , on 24 May 2018

In this post, Prof. Genoveva F. Esteban (Bournemouth University) goes hunting for protozoa at a Company of Biologists Workshop


This is the story of a journey that started a few years back with the finding of a rare community of single-celled organisms in a small and isolated nature reserve’s pond in Dorset. This microbial community was unusual in that the majority of these unicellular organisms were ‘protozoa’ (microbes that feed on other microbes) that harboured other microscopic life inside them; particularly interesting were those that harboured microscopic algae. Furthermore, most of the species had only been reported from one other location in the world – Germany!

Microscopic algae are plants and thus carry out photosynthesis. If we remember from our school years, photosynthesis is an outstanding biological mechanism allowing plants to produce their own food (i.e. carbohydrates) by using the sun’s energy; the waste product of this mechanism is oxygen, which is released into the environment. Interestingly, the protozoa that harbour the ‘endosymbiotic’ algae benefit from their photosynthesis in two ways; the first is as a nutritional source by taking up the carbohydrates produced through algal photosynthesis. This is not new as it has long been known that the majority of protozoa with endosymbiotic algae benefit from such a nutritional boost. However, this rare community of protozoa in a Dorset pond led us to discover that some protozoa did not use the photosynthetic nutritional rewards, but rather the oxygen produced as the end product of algal photosynthesis.

The protozoa with endosymbiotic algae are found in highly-productive ponds where oxygen levels are depleted; having an association with an oxygen-producing machine (the microscopic algae) seems the perfect arrangement. An example of this was the rare ciliated protozoan Loxodes rostrum (pictured) – an extremely unusual ciliate in many ways. Firstly, it has seldom ever been recorded (only in Germany and the UK, so far); secondly, it is a ciliate that harbours several different species of microscopic algae (most ciliate-algae associations are with one species only of the genus Chlorella). Unfortunately, the pond in Dorset dried out before we could finish our fascinating investigations on this unique species.

Fast forward a few years and I was invited to the Workshop Symbiosis in the Microbial World: from Ecology to Genome Evolution in November 2017, organised by The Company of Biologists on the impressive grounds of Wiston House (West Sussex). The site has an old and productive pond with ample overhanging vegetation – just like the pond in Dorset! Would this other pond have Loxodes rostrum? We collected samples for the workshop’s microscope session on ‘Life under the Lens’ that I was running, and voila – there it was, adding a new location to its biogeographic map. This finding at Wiston House allowed us to finalise the investigations on this ciliate species, including looking at its DNA sequence. The research is in collaboration with Prof Martin Embley and Dr Kacper Sendra at the Institute for Cell and Molecular Biosciences at Newcastle University.

We thank The Company of Biologists, particularly Nicky Le Blond for the enthusiasm and for facilitating pond sampling at Wiston House, and to the Wiston House estate for allowing access to the pond.

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