Composition and method for enhancing photosynthetic efficiency of microorganisms

Abstract

Compositions including metal nano- and/or micro-particles in solution with photosynthetic bioproduct producing microorganisms. These light harvesting complexes increase growth rates and photosynthetic efficiency of the constituent microorganisms, reducing the light required for a specific production level, or increases production for a specific light level.

Claims

1. A composition comprising a gold nano-particle complexed to a strain of F. diplosiphon having increased halotolerance relative to wild type strains of F. diplosiphon.

2. A composition according to claim 1, wherein the strain of F. diplosiphon having increased halotolerance relative to wild type strains of F. diplosiphon is suitable for use as a biofuel.

3. A composition according to claim 1, wherein the strain of F. diplosiphon having increased halotolerance relative to wild type strains of F. diplosiphon is a bioproduct producing microorganism.

4. A composition according to claim 3, wherein the strain of F. diplosiphon having increased halotolerance relative to wild type strains of F. diplosiphon produces a lipid selected from the group consisting of fats, waxes, sterols, fat-soluble vitamins, monoglycerides, diglycerides, triglycerides, and phospholipids.

5. A composition according to claim 3 wherein the strain of F. diplosiphon having increased halotolerance relative to wild type strains of F. diplosiphon produces a bioproduct selected from the group consisting of biopolymers, nutraceuticals and pharmaceuticals.

6. A composition according to claim 1, wherein the gold nano-particle is a nano-particle having a size of 20-100 nm.

7. A composition according to claim 1, wherein the gold nano-particle is a micro-particle having a size of 100-200 nm.

8. A composition according to claim 1, wherein the composition comprises both gold nano-particles complexed to said strain of F. diplosiphon having increased halotolerance relative to wild type strains of F. diplosiphon.

9. A composition according to claim 1, wherein the nano-particles have a shape selected from the group consisting of spheres, rods, fibers, films, wires, and tubes.

10. A composition according to claim 1 wherein the relative concentration of gold nano-micro-particles to cells of F. diplosiphon having increased halotolerance relative to wild type strains of F. diplosiphon is selected from the group consisting of 1:4, 1:2, 1:1, 2:1, and 4:1.

11. A composition according to claim 1, wherein in said composition comprises a gold nano-particle of 200 nm complexed to F. diplosiphon cells having increased halotolerance relative to wild type strains of F. diplosiphon in a ratio of 1:1.

12. A method for producing biofuels comprising growing the compositions according claim 1 in a bioreactor with an artificial light source having a specific and predetermined light wavelengths and/or light pulsations tuned to the absorbance profile of said compositions to increase microorganism growth and production of desired bioproducts.

13. A method according to claim 12, wherein said bioreactor is selected from the group consisting of batch, batch-fed, recycling, fluidized bed and/or hollow-fiber bioreactors.

14. A composition according to claim 1, wherein said composition has a faster growth rate than F. diplosiphon cells in the absence of gold nano-particles.

15. A composition according to claim 1, wherein said composition exhibits higher photosynthetic activity than F. diplosiphon cells in the absence of gold nano-particles.

16. A composition according to claim 1, wherein said composition exhibits enhanced spectral absorbance at wavelengths corresponding to Chlorophyll a than F. diplosiphon cells in the absence of gold nano-particles.

17. A composition according to claim 1, wherein said composition exhibits higher optical densities at 750 nm than native F. diplosiphon cells in the absence of gold nano-particles.

18. A composition according to claim 1, wherein said gold nano-particles comprise surface modifications that increase the strength of attachment of the gold nano-particles to cell surfaces of said F. diplosiphon having increased halotolerance relative to wild type strains of F. diplosiphon.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a representation of selected experiments that were used to demonstrate aspects of the invention.

(2) FIG. 2 is a line graph showing absorbance versus wavelength for F. diplosiphon cells loaded with gold nano-particles (“GNP”).

(3) FIG. 3 shows culture flasks containing F. diplosiphon cells loaded with different size gold-nano-particles (“AuNP) (top) and a bar graph showing optical densities at 750 nm for those cultures (bottom).

(4) FIG. 4 is a bar graph showing optical densities at 750 nm for cultures of F. diplosiphon cells loaded with different size gold nano-particles (“AuNP”) over time.

(5) FIG. 5 is a representation of a surface-modified gold nano-particle complexed to a photosynthetic microorganism.

DETAILED DESCRIPTION

(6) The inventors have developed artificial light harvesting complexes in F. diplosiphon using gold nano-particles, taking advantage of the discovery that the wavelengths of light at which gold nano-particles are excited correspond to the wavelengths of light that are utilized by F. diplosiphon for photosynthesis. FIG. 1 shows a graphic depiction of experiments conducted by the inventors in connection with the making of this invention, using gold nano-particles with F. diplosiphon cells. Gold nano-particles are non-toxic to the growth of F. diplosiphon, and FIG. 2 shows that the nano-cultures (gold nano-particles in solution with F. diplosiphon cells) have a faster growth rate than F. diplosiphon non-complexed cell cultures. More specifically, FIG. 2 shows that a 1:1 ratio of 20 nm gold nano-particles to F. diplosiphon cells produces enhanced spectral absorbance at wavelengths corresponding to chlorophyll a and phycobiliproteins as well as at 750 nm (orange and blue lines), indicating an increase in photosynthetic pigment accumulation after 48 hrs.

(7) Additionally, cultures of F. diplosiphon exposed to gold nano-particles exhibited higher optical densities at 750 nm (OD.sub.750), which is commonly used to measure culture growth since changes in pigmentation will not interfere with absorbance at this wavelength. Referring to FIG. 3, F. diplosiphon was cultivated in culture flasks without nano-particles (flask a), and in solution with 20 nm (flask b), 100 nm (flask c), and 200 nm (flask d) gold colloids, see top of FIG. 3. After nine days, a significant increase in F. diplosiphon growth (measured by OD.sub.750) was observed in cultures treated with 20, 100, and 200 nm gold nano-particles with maximum increase in growth observed in cultures treated with 200 nm gold nano-particles (“AuNPs”), see data bottom of FIG. 3. Cells grown in the absence of gold nano-particles served as positive control (PC) and gold colloids alone served as negative controls (NC).

(8) In addition, impact of 20, 100, and 200 nm-diameter AuNPs on F. diplosiphon growth was determined by measuring OD.sub.750 over a period of 15 days. Cells grown in the absence of AuNPs served as positive control (PC) and AuNP suspensions served as negative controls (NC). While all other treatments achieved peak growth by the ninth day, cultures in solution with 20 nm AuNPs exhibited prolonged growth to 11 days (FIG. 4).

(9) FIG. 5 shows self-assembled monolayers of alkane thiols binding to the surface of the AuNPs to enhance photosynthesis of a complexed microorganism. Such surface modifications can provide a stronger attachment of the nanoparticle to the cell surface, further enhancing light capture and scatter, and hence photosynthetic pigment accumulation, lipid and other bio-product production.