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Potential for luxS related signalling in marine bacteria and production of autoinducer-2 in the genus Shewanella.

Bodor A, Elxnat B, Thiel V, Schulz S, Wagner-Döbler I - BMC Microbiol. (2008)

Bottom Line: The luxS gene coding for the AI-2 synthase enzyme was found in many important pathogens.Within the Gammaproteobacteria (n = 76), luxS was found in all Shewanella, Vibrio and Alteromonas isolates and some Pseudoalteromonas and Halomonas species, while sahH was detected in Psychrobacter strains.A number of Gammaproteobacteria (n = 27) appeared to have neither the luxS nor the sahH gene.

View Article: PubMed Central - HTML - PubMed

Affiliation: Helmholtz-Center for Infection Research, Group Microbial Communication, Division of Cell Biology, Inhoffenstr, 7, 38124 Braunschweig, Germany. agb@gbf.de

ABSTRACT

Background: The autoinducer-2 (AI-2) group of signalling molecules are produced by both Gram positive and Gram negative bacteria as the by-product of a metabolic transformation carried out by the LuxS enzyme. They are the only non species-specific quorum sensing compounds presently known in bacteria. The luxS gene coding for the AI-2 synthase enzyme was found in many important pathogens. Here, we surveyed its occurrence in a collection of 165 marine isolates belonging to abundant marine phyla using conserved degenerated PCR primers and sequencing of selected positive bands to determine if the presence of the luxS gene is phylogenetically conserved or dependent on the habitat.

Results: The luxS gene was not present in any of the Alphaproteobacteria (n = 71) and Bacteroidetes strains (n = 29) tested; by contrast, these bacteria harboured the sahH gene, coding for an alternative enzyme for the detoxification of S-adenosylhomocysteine (SAH) in the activated methyl cycle. Within the Gammaproteobacteria (n = 76), luxS was found in all Shewanella, Vibrio and Alteromonas isolates and some Pseudoalteromonas and Halomonas species, while sahH was detected in Psychrobacter strains. A number of Gammaproteobacteria (n = 27) appeared to have neither the luxS nor the sahH gene. We then studied the production of AI-2 in the genus Shewanella using the Vibrio harveyi bioassay. All ten species of Shewanella tested produced a pronounced peak of AI-2 towards the end of the exponential growth phase in several media investigated. The maximum of AI-2 activity was different in each Shewanella species, ranging from 4% to 46% of the positive control.

Conclusion: The data are consistent with those of fully sequenced bacterial genomes and show that the potential for luxS related signalling is dependent on phylogenetic affiliation rather than ecological niche and is largest in certain groups of Gammaproteobacteria in the marine environment. This is the first report on AI-2 production in Shewanella species; its signalling role in these organisms remains to be elucidated.

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Effect of growth phase (A) and medium (B) on AI-2 production in representative species of the genus Shewanella. (A) Comparison between a Shewanella species with low (A. fetalis) and high (S. japonica) maximum AI-2 level. (B) AI-2 levels during growth for S. hafniensis DT-1 cultivated in marine broth (MB) and in Luria Bertani medium with sea salts (LBSS). Fold induction values are given as percentage of the positive control. Standard deviations are given for 4 replicate measurements of the same sample within a bioassay.
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Figure 2: Effect of growth phase (A) and medium (B) on AI-2 production in representative species of the genus Shewanella. (A) Comparison between a Shewanella species with low (A. fetalis) and high (S. japonica) maximum AI-2 level. (B) AI-2 levels during growth for S. hafniensis DT-1 cultivated in marine broth (MB) and in Luria Bertani medium with sea salts (LBSS). Fold induction values are given as percentage of the positive control. Standard deviations are given for 4 replicate measurements of the same sample within a bioassay.

Mentions: Several of the Gammaproteobacteria species which did not have the luxS gene were tested for AI-2 activity using the V. harveyi bioassay. AI-2 could not be detected, confirming the PCR result (data not shown). All Shewanella and Alishewanella strains contained the luxS gene and were tested for AI-2 activity, which was detected in all of them. Table 2 shows the summary of all 73 bioassays conducted; for each species, the maximum A1-2 activity is averaged for the indicated number of bioassays. Average maximum fold induction values were between 4% (e.g. S. hafniensis, S. marinintestina) and 46% (S. japonica). Figure 1 shows a subset of these data; for each species, two different cultures are shown, each of which was tested in two different bioassays independently. Variability between cultures and between replicate bioassays was sometimes very high. Independent of the level of AI-2 activity detected, the same growth phase dependent pattern of production was observed in all investigated strains. Fig. 2A shows this for two representative species, A. fetalis with low, and S. japonica with high maximum AI-2 activity. In all Shewanella strains AI-2 activity reached its maximum towards the end of the exponential growth phase and decreased during stationary phase. In species with high AI-2 activity, this decrease occurred gradually. By contrast, if the AI-2 activity was low, it disappeared rapidly at the beginning of the stationary phase within 2 – 4 hours. At the late stationary phase (after 24 h of growth), no AI-2 activity was detected in any of the strains tested. The same pattern was observed in all cultivation media used. As an example, Fig. 2B shows AI-2 production of S. hafniensis DT-1 in two different media. The strain produced similar AI-2 activities at the same growth phase in both of them. S. oneidensis was also cultivated anaerobically using iron as an electron acceptor (with 10 and 20 mM ferric citrate, respectively). Under these conditions, growth was very slow and AI-2 activity was not found (data not shown).


Potential for luxS related signalling in marine bacteria and production of autoinducer-2 in the genus Shewanella.

Bodor A, Elxnat B, Thiel V, Schulz S, Wagner-Döbler I - BMC Microbiol. (2008)

Effect of growth phase (A) and medium (B) on AI-2 production in representative species of the genus Shewanella. (A) Comparison between a Shewanella species with low (A. fetalis) and high (S. japonica) maximum AI-2 level. (B) AI-2 levels during growth for S. hafniensis DT-1 cultivated in marine broth (MB) and in Luria Bertani medium with sea salts (LBSS). Fold induction values are given as percentage of the positive control. Standard deviations are given for 4 replicate measurements of the same sample within a bioassay.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2233627&req=5

Figure 2: Effect of growth phase (A) and medium (B) on AI-2 production in representative species of the genus Shewanella. (A) Comparison between a Shewanella species with low (A. fetalis) and high (S. japonica) maximum AI-2 level. (B) AI-2 levels during growth for S. hafniensis DT-1 cultivated in marine broth (MB) and in Luria Bertani medium with sea salts (LBSS). Fold induction values are given as percentage of the positive control. Standard deviations are given for 4 replicate measurements of the same sample within a bioassay.
Mentions: Several of the Gammaproteobacteria species which did not have the luxS gene were tested for AI-2 activity using the V. harveyi bioassay. AI-2 could not be detected, confirming the PCR result (data not shown). All Shewanella and Alishewanella strains contained the luxS gene and were tested for AI-2 activity, which was detected in all of them. Table 2 shows the summary of all 73 bioassays conducted; for each species, the maximum A1-2 activity is averaged for the indicated number of bioassays. Average maximum fold induction values were between 4% (e.g. S. hafniensis, S. marinintestina) and 46% (S. japonica). Figure 1 shows a subset of these data; for each species, two different cultures are shown, each of which was tested in two different bioassays independently. Variability between cultures and between replicate bioassays was sometimes very high. Independent of the level of AI-2 activity detected, the same growth phase dependent pattern of production was observed in all investigated strains. Fig. 2A shows this for two representative species, A. fetalis with low, and S. japonica with high maximum AI-2 activity. In all Shewanella strains AI-2 activity reached its maximum towards the end of the exponential growth phase and decreased during stationary phase. In species with high AI-2 activity, this decrease occurred gradually. By contrast, if the AI-2 activity was low, it disappeared rapidly at the beginning of the stationary phase within 2 – 4 hours. At the late stationary phase (after 24 h of growth), no AI-2 activity was detected in any of the strains tested. The same pattern was observed in all cultivation media used. As an example, Fig. 2B shows AI-2 production of S. hafniensis DT-1 in two different media. The strain produced similar AI-2 activities at the same growth phase in both of them. S. oneidensis was also cultivated anaerobically using iron as an electron acceptor (with 10 and 20 mM ferric citrate, respectively). Under these conditions, growth was very slow and AI-2 activity was not found (data not shown).

Bottom Line: The luxS gene coding for the AI-2 synthase enzyme was found in many important pathogens.Within the Gammaproteobacteria (n = 76), luxS was found in all Shewanella, Vibrio and Alteromonas isolates and some Pseudoalteromonas and Halomonas species, while sahH was detected in Psychrobacter strains.A number of Gammaproteobacteria (n = 27) appeared to have neither the luxS nor the sahH gene.

View Article: PubMed Central - HTML - PubMed

Affiliation: Helmholtz-Center for Infection Research, Group Microbial Communication, Division of Cell Biology, Inhoffenstr, 7, 38124 Braunschweig, Germany. agb@gbf.de

ABSTRACT

Background: The autoinducer-2 (AI-2) group of signalling molecules are produced by both Gram positive and Gram negative bacteria as the by-product of a metabolic transformation carried out by the LuxS enzyme. They are the only non species-specific quorum sensing compounds presently known in bacteria. The luxS gene coding for the AI-2 synthase enzyme was found in many important pathogens. Here, we surveyed its occurrence in a collection of 165 marine isolates belonging to abundant marine phyla using conserved degenerated PCR primers and sequencing of selected positive bands to determine if the presence of the luxS gene is phylogenetically conserved or dependent on the habitat.

Results: The luxS gene was not present in any of the Alphaproteobacteria (n = 71) and Bacteroidetes strains (n = 29) tested; by contrast, these bacteria harboured the sahH gene, coding for an alternative enzyme for the detoxification of S-adenosylhomocysteine (SAH) in the activated methyl cycle. Within the Gammaproteobacteria (n = 76), luxS was found in all Shewanella, Vibrio and Alteromonas isolates and some Pseudoalteromonas and Halomonas species, while sahH was detected in Psychrobacter strains. A number of Gammaproteobacteria (n = 27) appeared to have neither the luxS nor the sahH gene. We then studied the production of AI-2 in the genus Shewanella using the Vibrio harveyi bioassay. All ten species of Shewanella tested produced a pronounced peak of AI-2 towards the end of the exponential growth phase in several media investigated. The maximum of AI-2 activity was different in each Shewanella species, ranging from 4% to 46% of the positive control.

Conclusion: The data are consistent with those of fully sequenced bacterial genomes and show that the potential for luxS related signalling is dependent on phylogenetic affiliation rather than ecological niche and is largest in certain groups of Gammaproteobacteria in the marine environment. This is the first report on AI-2 production in Shewanella species; its signalling role in these organisms remains to be elucidated.

Show MeSH
Related in: MedlinePlus