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Discovery of Bioactive Metabolites in Biofuel Microalgae That Offer Protection against Predatory Bacteria.

Bagwell CE, Abernathy A, Barnwell R, Milliken CE, Noble PA, Dale T, Beauchesne KR, Moeller PD - Front Microbiol (2016)

Bottom Line: Even though Chlorophytes are generally regarded safe for human consumption, there is still much we do not understand about the metabolic and biochemical potential of microscopic algae.Introduction of V. chlorellavorus resulted in a 72% decrease in algal biomass in the experimental controls after 7 days.Further study of this phenomenon could contribute to the development of new strategies to extend algal production cycles in open, outdoor systems while ensuring the protection of biomass from predatory losses.

View Article: PubMed Central - PubMed

Affiliation: Environmental Sciences and Biotechnology, Savannah River National Laboratory, Aiken SC, USA.

ABSTRACT
Microalgae could become an important resource for addressing increasing global demand for food, energy, and commodities while helping to reduce atmospheric greenhouse gasses. Even though Chlorophytes are generally regarded safe for human consumption, there is still much we do not understand about the metabolic and biochemical potential of microscopic algae. The aim of this study was to evaluate biofuel candidate strains of Chlorella and Scenedesmus for the potential to produce bioactive metabolites when grown under nutrient depletion regimes intended to stimulate production of triacylglycerides. Strain specific combinations of macro- and micro-nutrient restricted growth media did stimulate neutral lipid accumulation by microalgal cultures. However, cultures that were restricted for iron consistently and reliably tested positive for cytotoxicity by in vivo bioassays. The addition of iron back to these cultures resulted in the disappearance of the bioactive components by LC/MS fingerprinting and loss of cytotoxicity by in vivo bioassay. Incomplete NMR characterization of the most abundant cytotoxic fractions suggested that small molecular weight peptides and glycosides could be responsible for Chlorella cytotoxicity. Experiments were conducted to determine if the bioactive metabolites induced by Fe-limitation in Chlorella sp. cultures would elicit protection against Vampirovibrio chlorellavorus, an obligate predator of Chlorella. Introduction of V. chlorellavorus resulted in a 72% decrease in algal biomass in the experimental controls after 7 days. Conversely, only slight losses of algal biomass were measured for the iron limited Chlorella cultures (0-9%). This study demonstrates a causal linkage between iron bioavailability and bioactive metabolite production in strains of Chlorella and Scenedesmus. Further study of this phenomenon could contribute to the development of new strategies to extend algal production cycles in open, outdoor systems while ensuring the protection of biomass from predatory losses.

No MeSH data available.


Related in: MedlinePlus

Chlorella culture under attack by Vampirovibrio chlorellavorus. (A) Shows V. chlorellavorus (rods) seeking out and contacting algal cells. (B) Shows epibionts (coccoids) attached to host cells. (C) Shows the aftermath of lysed and degraded algal cells.
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Figure 4: Chlorella culture under attack by Vampirovibrio chlorellavorus. (A) Shows V. chlorellavorus (rods) seeking out and contacting algal cells. (B) Shows epibionts (coccoids) attached to host cells. (C) Shows the aftermath of lysed and degraded algal cells.

Mentions: Chlorella biomass was prepared under iron limited conditions and methanol soluble fractions were assayed for cytotoxicity as described previously. Treatment 4 biomass (1/10 total iron), again, consistently generated highly bioactive preparations; fourfold dilution of the extract did not decrease cytotoxicity. Treatment 5 biomass, however, elicited a weak but detectable response only when bioassays were conducted with full strength (4 μl) preparations. Iron limited (cytotoxicity confirmed) and control Chlorella cultures were then incubated with the predator in the dark to suspend photoautotrophic growth of the host alga. Additionally, cultures were maintained in the depleted growth medium to preserve the physiological state (cytotoxic phenotype) of the host cultures for the duration of the experiment. Predation by V. chlorellavorus effectively destroyed the control cultures (Figure 4); viable cell counts were reduced on average by 72% in 7 days. Remarkably, no detectable cell loss was measured for Treatment 4 cultures (high level of relative cytotoxicity), and averaged viable cell loss for Treatment 5 cultures (low level of relative cytotoxicity) was only 9%. In a parallel experiment, iron was reintroduced by transferring the cytotoxic cultures to fresh M8 medium. Predatory losses for these cultures averaged 0 and 57% for Treatments 4 and 5, respectively. Standard deviation around the averaged cell counts did not exceed 15% for any of these experimental treatments. These results reinforce the postulated linkage between iron availability and the synthesis and potency of bioactive metabolites in this Chlorella strain. Importantly, the bioactive metabolites induced by iron limitation protected Chlorella biomass against epibiotic predation by V. chlorellavorus.


Discovery of Bioactive Metabolites in Biofuel Microalgae That Offer Protection against Predatory Bacteria.

Bagwell CE, Abernathy A, Barnwell R, Milliken CE, Noble PA, Dale T, Beauchesne KR, Moeller PD - Front Microbiol (2016)

Chlorella culture under attack by Vampirovibrio chlorellavorus. (A) Shows V. chlorellavorus (rods) seeking out and contacting algal cells. (B) Shows epibionts (coccoids) attached to host cells. (C) Shows the aftermath of lysed and degraded algal cells.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4834574&req=5

Figure 4: Chlorella culture under attack by Vampirovibrio chlorellavorus. (A) Shows V. chlorellavorus (rods) seeking out and contacting algal cells. (B) Shows epibionts (coccoids) attached to host cells. (C) Shows the aftermath of lysed and degraded algal cells.
Mentions: Chlorella biomass was prepared under iron limited conditions and methanol soluble fractions were assayed for cytotoxicity as described previously. Treatment 4 biomass (1/10 total iron), again, consistently generated highly bioactive preparations; fourfold dilution of the extract did not decrease cytotoxicity. Treatment 5 biomass, however, elicited a weak but detectable response only when bioassays were conducted with full strength (4 μl) preparations. Iron limited (cytotoxicity confirmed) and control Chlorella cultures were then incubated with the predator in the dark to suspend photoautotrophic growth of the host alga. Additionally, cultures were maintained in the depleted growth medium to preserve the physiological state (cytotoxic phenotype) of the host cultures for the duration of the experiment. Predation by V. chlorellavorus effectively destroyed the control cultures (Figure 4); viable cell counts were reduced on average by 72% in 7 days. Remarkably, no detectable cell loss was measured for Treatment 4 cultures (high level of relative cytotoxicity), and averaged viable cell loss for Treatment 5 cultures (low level of relative cytotoxicity) was only 9%. In a parallel experiment, iron was reintroduced by transferring the cytotoxic cultures to fresh M8 medium. Predatory losses for these cultures averaged 0 and 57% for Treatments 4 and 5, respectively. Standard deviation around the averaged cell counts did not exceed 15% for any of these experimental treatments. These results reinforce the postulated linkage between iron availability and the synthesis and potency of bioactive metabolites in this Chlorella strain. Importantly, the bioactive metabolites induced by iron limitation protected Chlorella biomass against epibiotic predation by V. chlorellavorus.

Bottom Line: Even though Chlorophytes are generally regarded safe for human consumption, there is still much we do not understand about the metabolic and biochemical potential of microscopic algae.Introduction of V. chlorellavorus resulted in a 72% decrease in algal biomass in the experimental controls after 7 days.Further study of this phenomenon could contribute to the development of new strategies to extend algal production cycles in open, outdoor systems while ensuring the protection of biomass from predatory losses.

View Article: PubMed Central - PubMed

Affiliation: Environmental Sciences and Biotechnology, Savannah River National Laboratory, Aiken SC, USA.

ABSTRACT
Microalgae could become an important resource for addressing increasing global demand for food, energy, and commodities while helping to reduce atmospheric greenhouse gasses. Even though Chlorophytes are generally regarded safe for human consumption, there is still much we do not understand about the metabolic and biochemical potential of microscopic algae. The aim of this study was to evaluate biofuel candidate strains of Chlorella and Scenedesmus for the potential to produce bioactive metabolites when grown under nutrient depletion regimes intended to stimulate production of triacylglycerides. Strain specific combinations of macro- and micro-nutrient restricted growth media did stimulate neutral lipid accumulation by microalgal cultures. However, cultures that were restricted for iron consistently and reliably tested positive for cytotoxicity by in vivo bioassays. The addition of iron back to these cultures resulted in the disappearance of the bioactive components by LC/MS fingerprinting and loss of cytotoxicity by in vivo bioassay. Incomplete NMR characterization of the most abundant cytotoxic fractions suggested that small molecular weight peptides and glycosides could be responsible for Chlorella cytotoxicity. Experiments were conducted to determine if the bioactive metabolites induced by Fe-limitation in Chlorella sp. cultures would elicit protection against Vampirovibrio chlorellavorus, an obligate predator of Chlorella. Introduction of V. chlorellavorus resulted in a 72% decrease in algal biomass in the experimental controls after 7 days. Conversely, only slight losses of algal biomass were measured for the iron limited Chlorella cultures (0-9%). This study demonstrates a causal linkage between iron bioavailability and bioactive metabolite production in strains of Chlorella and Scenedesmus. Further study of this phenomenon could contribute to the development of new strategies to extend algal production cycles in open, outdoor systems while ensuring the protection of biomass from predatory losses.

No MeSH data available.


Related in: MedlinePlus