287
did not cause a morphological change in the coccolith-bearing strain, it did cause
increased size and membrane permeability in the bald strain, indicating a signalling
role between cell types of the alga (Labeeuw et al. 2016).
14.2.2 Commensalism
The ability of bacteria to switch from a mutualistic to pathogenic interaction is
attributed to environmental factors (Valiente-Banuet and Verdú 2008; Ramanan
et al. 2016). One theory is that there is a continuum of interactions and bacteria
pass through a stage of commensalism on the way to pathogenicity (Zapalski
2011). Another theory put forth is that the end stage of many mutualists and parasites is naturally as commensals (Sachs and Simms 2006). The study of commensals is complicated, as they are difficult to distinguish from mutualists. There are
often ‘satellite’ or epiphytic bacterial communities described on algal hosts, but
these studies have not investigated how the algae might be benefiting from the
relationship (Schäfer and Abbas 2002; Tujula et al. 2010). Experiments have
shown that adding in natural bacterial communities to axenic algal strains can
have a distinct effect on the host growth and survival (Grossart et al. 2005; Bolch
et al. 2011). There are many examples of stable communities of bacteria living
with algae, with the bacteria benefiting from the leaked nutrients from the algae;
however, it is difficult to prove the absence of some algal benefit, thereby proving
them to be true commensals rather than mutualists (Cole 1982; Bratbak and
Thingstad 1985).
14.3 Negative Interactions
14.3.1 Parasitism
Parasitism, whereby one species benefits at the expense of the overall health and
fecundity of its host, is found between algae and bacteria, or between algal species,
as algae can often act parasitically to other algae. For example, approximately 10%
of red algae are parasites of other, free-living, red algae (Hancock et al. 2010).
Fungi, amoebae, alveolates as well as other protists and other algae species (often
of the same phylum) are known to be parasites of microalgae as well (Park et al.
2004; Carney and Lane 2014). Parasitism can lead to the premature demise of the
algal bloom population (Grami et al. 2011). Parasites are important for the resilience of a system against perturbation and ecosystem functioning (Gachon et al.
2010). However, the effects of bacterial parasitism and the chemical signals and
metabolites underpinning these interactions are largely unresolved and an area for
future studies.
14 Bioactive Small Molecules Mediate Microalgal-Bacterial Interactions
did not cause a morphological change in the coccolith-bearing strain, it did cause
increased size and membrane permeability in the bald strain, indicating a signalling
role between cell types of the alga (Labeeuw et al. 2016).
14.2.2 Commensalism
The ability of bacteria to switch from a mutualistic to pathogenic interaction is
attributed to environmental factors (Valiente-Banuet and Verdú 2008; Ramanan
et al. 2016). One theory is that there is a continuum of interactions and bacteria
pass through a stage of commensalism on the way to pathogenicity (Zapalski
2011). Another theory put forth is that the end stage of many mutualists and parasites is naturally as commensals (Sachs and Simms 2006). The study of commensals is complicated, as they are difficult to distinguish from mutualists. There are
often ‘satellite’ or epiphytic bacterial communities described on algal hosts, but
these studies have not investigated how the algae might be benefiting from the
relationship (Schäfer and Abbas 2002; Tujula et al. 2010). Experiments have
shown that adding in natural bacterial communities to axenic algal strains can
have a distinct effect on the host growth and survival (Grossart et al. 2005; Bolch
et al. 2011). There are many examples of stable communities of bacteria living
with algae, with the bacteria benefiting from the leaked nutrients from the algae;
however, it is difficult to prove the absence of some algal benefit, thereby proving
them to be true commensals rather than mutualists (Cole 1982; Bratbak and
Thingstad 1985).
14.3 Negative Interactions
14.3.1 Parasitism
Parasitism, whereby one species benefits at the expense of the overall health and
fecundity of its host, is found between algae and bacteria, or between algal species,
as algae can often act parasitically to other algae. For example, approximately 10%
of red algae are parasites of other, free-living, red algae (Hancock et al. 2010).
Fungi, amoebae, alveolates as well as other protists and other algae species (often
of the same phylum) are known to be parasites of microalgae as well (Park et al.
2004; Carney and Lane 2014). Parasitism can lead to the premature demise of the
algal bloom population (Grami et al. 2011). Parasites are important for the resilience of a system against perturbation and ecosystem functioning (Gachon et al.
2010). However, the effects of bacterial parasitism and the chemical signals and
metabolites underpinning these interactions are largely unresolved and an area for
future studies.
14 Bioactive Small Molecules Mediate Microalgal-Bacterial Interactions