305
lence of the plant pathogen (Ferluga and Venturi 2009). Interestingly VarR, a type of
solo LuxR, is also identified from macroalgae-associated bacterial pathogen
Nautella italica R11 (Fernandes et al. 2011). The strain has been identified to induce
the bleaching disease in vivo and in vitro in Delisea pulchra (Campbell et al. 2011;
Fernandes et al. 2011). Via a combination of allelic exchange mutagenesis, physiological characterization and high-throughput proteomics, Gardiner et al. (2015)
found evidence for varR to act as a regulator of colonization and virulence in this
organism. Particularly, the study observed that 3.4% of the predicted proteome of N.
italica R11 was differentially expressed between planktonic and biofilm conditions
of varR mutant as compared to wild type. Thus, a subset of biofilm-associated protein of N. italica R11 is controlled by solo varR indicating their importance in
attachment, biofilm maturation and infection in D. pulchra.
Cross kingdom communication through QS exists between bacteria and macroalgae. AHL molecules increase zoospore settlement in green macroalgae (Joint
et al. 2002) and promote carpospore liberation in some red macroalgae (Weinberger
et al. 2007; Singh et al. 2015). Joint et al. (2002) demonstrated that zoospores of
Enteromorpha species respond to biofilm of the Vibrio anguillarum. V. anguillarum
is a Gram-negative bacterium and can be able to produce C6-HSL, 3-hydroxy-C6HSL and 3-oxo-C10-HSL (Milton et al. 1997). Tait et al. (2005) determined the
rational effect of these AHLs on zoospore settlement and observed that longer
N-acyl side-chains tended to result in increasing zoospore settlement. Furthermore,
availability of 3-hydroxy and 3-oxo at C3 of acyl chain makes them more active
AHLs than C6-HSL and C10-HSL towards zoospore settlement. When a lactonasecoding gene (that degrades AHLs) aiiA was expressed into V. anguillarum, the
recombinant strain lost the activity of enhancing zoospore settlement, providing
strong support for the involvement of AHLs (Joint et al. 2002). Wheeler et al. (2006)
used wild and vanM mutant types of V. anguillarum and defined that the orientation
of zoospores does not change during settlement and their swimming speed decreases
more rapidly on the wild-type V. anguillarum biofilms as compared to vanM mutant.
Thus, it is presumed that chemokinesis mechanism operates instead of chemotactic
in which zoospore swimming speed rapidly decreases in the presence of AHLs.
Further, experiments on this system suggested that AHLs influence Ca
2+
influx in
the zoospores which preferentially induced the settlement of them on bacterial biofilms producing AHLs (Wheeler et al. 2006; Joint et al. 2007).
Intriguingly, whilst AHLs promote zoospore settlement in the Ulva, they have a
negative impact on germination and early growth stages of settled zoospores (Twigg
et al. 2014). Using both native AHL producers (i.e. Sulfitobacter spp. 376 and
Shewanella spp. 79) and synthetic AHLs, Twigg et al. (2014) could show that germling length was significantly reduced in the presence of AHLs or AHL-producing
biofilms compared to the controls. The authors hypothesised that this apparent paradox (i.e. AHL induction of settlement yet retardation of germination and early
growth) could be explained by the fact that slower growing algae can outcompete
fast growers in nutrient-limited environments (Twigg et al. 2014). Thus, these results
provide further evidence of the complexity of bacterial-macroalgal interactions and
15 Exploring the Complexity of Macroalgal-Bacterial Interactions…
lence of the plant pathogen (Ferluga and Venturi 2009). Interestingly VarR, a type of
solo LuxR, is also identified from macroalgae-associated bacterial pathogen
Nautella italica R11 (Fernandes et al. 2011). The strain has been identified to induce
the bleaching disease in vivo and in vitro in Delisea pulchra (Campbell et al. 2011;
Fernandes et al. 2011). Via a combination of allelic exchange mutagenesis, physiological characterization and high-throughput proteomics, Gardiner et al. (2015)
found evidence for varR to act as a regulator of colonization and virulence in this
organism. Particularly, the study observed that 3.4% of the predicted proteome of N.
italica R11 was differentially expressed between planktonic and biofilm conditions
of varR mutant as compared to wild type. Thus, a subset of biofilm-associated protein of N. italica R11 is controlled by solo varR indicating their importance in
attachment, biofilm maturation and infection in D. pulchra.
Cross kingdom communication through QS exists between bacteria and macroalgae. AHL molecules increase zoospore settlement in green macroalgae (Joint
et al. 2002) and promote carpospore liberation in some red macroalgae (Weinberger
et al. 2007; Singh et al. 2015). Joint et al. (2002) demonstrated that zoospores of
Enteromorpha species respond to biofilm of the Vibrio anguillarum. V. anguillarum
is a Gram-negative bacterium and can be able to produce C6-HSL, 3-hydroxy-C6HSL and 3-oxo-C10-HSL (Milton et al. 1997). Tait et al. (2005) determined the
rational effect of these AHLs on zoospore settlement and observed that longer
N-acyl side-chains tended to result in increasing zoospore settlement. Furthermore,
availability of 3-hydroxy and 3-oxo at C3 of acyl chain makes them more active
AHLs than C6-HSL and C10-HSL towards zoospore settlement. When a lactonasecoding gene (that degrades AHLs) aiiA was expressed into V. anguillarum, the
recombinant strain lost the activity of enhancing zoospore settlement, providing
strong support for the involvement of AHLs (Joint et al. 2002). Wheeler et al. (2006)
used wild and vanM mutant types of V. anguillarum and defined that the orientation
of zoospores does not change during settlement and their swimming speed decreases
more rapidly on the wild-type V. anguillarum biofilms as compared to vanM mutant.
Thus, it is presumed that chemokinesis mechanism operates instead of chemotactic
in which zoospore swimming speed rapidly decreases in the presence of AHLs.
Further, experiments on this system suggested that AHLs influence Ca
2+
influx in
the zoospores which preferentially induced the settlement of them on bacterial biofilms producing AHLs (Wheeler et al. 2006; Joint et al. 2007).
Intriguingly, whilst AHLs promote zoospore settlement in the Ulva, they have a
negative impact on germination and early growth stages of settled zoospores (Twigg
et al. 2014). Using both native AHL producers (i.e. Sulfitobacter spp. 376 and
Shewanella spp. 79) and synthetic AHLs, Twigg et al. (2014) could show that germling length was significantly reduced in the presence of AHLs or AHL-producing
biofilms compared to the controls. The authors hypothesised that this apparent paradox (i.e. AHL induction of settlement yet retardation of germination and early
growth) could be explained by the fact that slower growing algae can outcompete
fast growers in nutrient-limited environments (Twigg et al. 2014). Thus, these results
provide further evidence of the complexity of bacterial-macroalgal interactions and
15 Exploring the Complexity of Macroalgal-Bacterial Interactions…