26.5.3 Cilliates and their Photosynthetic Endosymbionts
Ciliates have acquired photosynthetic capablility by ingesting and then retaining
either intact viable algae as endosymbionts or keeping just the chloroplasts. Four of
these ciliate groups are represented in Fig. 26.20.
Paramecium bursaria (He et al. 2019) and Stentor polymorphus (Wagner 2015)
are examples of ciliates that ingest Chlorella algae and then retain those algae as
viable endosymbionts. These two species of ciliate are presented on the right side of
Fig. 26.20. Kodama and Fujishima (2015) have determined that infectivity of the
Chlorella symbiont for Paramecium differs based upon the growth phase of the
Chlorella.
Laboea strobila and Myrionecta rubra are examples of ciliates that eat algae but
internally retain only the chloroplasts, and whether these accumulated chloroplasts
can be called kleptoplasts is a technicality still being debated. These two species of
ciliate are presented on the left side of Fig. 26.20.
Stoecker et al. (1988) helped to define our understanding of how Laboea strobila
utilizes its accumulated chloroplasts. The chloroplasts of Myrionecta rubra are in
turn ingested, and presumably used, by dinoflagellates which feed upon the
Myrionecta (Park et al. 2006).
26.6 The Provision of Nitrogen by Microbial Symbionts
of Plants
With all plants possessing mitochondria and chloroplasts, the ecological competition
between plants may have seemed more balanced. So, then, what might have come
along next as a way of gaining a competitive edge? I would guess that finding ones
own source of fixed nitrogen that could be delivered directly to their roots may have
been the next effort that plants made for gaining an evolutionary benefit by cheating
against their competitors.
It is hard to know where and when this round of competition began. Fixed
nitrogen has become the common currency for many symbiotic interactions. The
need for plants to gain symbiotic associations with microbes that could provide fixed
nitrogen might have resulted in plants initially sharing their roots with cyanobacteria.
For that reason, I will start this part of my essay by presenting examples of nitrogen
being supplied to plant roots by symbiotic cyanobacteria, which likely also had been
the source of chloroplasts. Today, we know those nitrogen-providing microbes as
Anabaena, Calothrix and Nostoc, which are members of the phylum Cyanobacteria,
order Nostocales.
But, there also are two additional options that have survived until the present day.
The proteobacteria provided one of those options, we know these successful
microbes as Rhizobium and their close relatives. The name Rhizobium represents a
genus and also is the name of a more general taxonomic group, both of which belong
568
C. J. Hurst
Ciliates have acquired photosynthetic capablility by ingesting and then retaining
either intact viable algae as endosymbionts or keeping just the chloroplasts. Four of
these ciliate groups are represented in Fig. 26.20.
Paramecium bursaria (He et al. 2019) and Stentor polymorphus (Wagner 2015)
are examples of ciliates that ingest Chlorella algae and then retain those algae as
viable endosymbionts. These two species of ciliate are presented on the right side of
Fig. 26.20. Kodama and Fujishima (2015) have determined that infectivity of the
Chlorella symbiont for Paramecium differs based upon the growth phase of the
Chlorella.
Laboea strobila and Myrionecta rubra are examples of ciliates that eat algae but
internally retain only the chloroplasts, and whether these accumulated chloroplasts
can be called kleptoplasts is a technicality still being debated. These two species of
ciliate are presented on the left side of Fig. 26.20.
Stoecker et al. (1988) helped to define our understanding of how Laboea strobila
utilizes its accumulated chloroplasts. The chloroplasts of Myrionecta rubra are in
turn ingested, and presumably used, by dinoflagellates which feed upon the
Myrionecta (Park et al. 2006).
26.6 The Provision of Nitrogen by Microbial Symbionts
of Plants
With all plants possessing mitochondria and chloroplasts, the ecological competition
between plants may have seemed more balanced. So, then, what might have come
along next as a way of gaining a competitive edge? I would guess that finding ones
own source of fixed nitrogen that could be delivered directly to their roots may have
been the next effort that plants made for gaining an evolutionary benefit by cheating
against their competitors.
It is hard to know where and when this round of competition began. Fixed
nitrogen has become the common currency for many symbiotic interactions. The
need for plants to gain symbiotic associations with microbes that could provide fixed
nitrogen might have resulted in plants initially sharing their roots with cyanobacteria.
For that reason, I will start this part of my essay by presenting examples of nitrogen
being supplied to plant roots by symbiotic cyanobacteria, which likely also had been
the source of chloroplasts. Today, we know those nitrogen-providing microbes as
Anabaena, Calothrix and Nostoc, which are members of the phylum Cyanobacteria,
order Nostocales.
But, there also are two additional options that have survived until the present day.
The proteobacteria provided one of those options, we know these successful
microbes as Rhizobium and their close relatives. The name Rhizobium represents a
genus and also is the name of a more general taxonomic group, both of which belong
568
C. J. Hurst