Method for determining a concentration of lipids in a microorganism

1. A method for determining a concentration of lipids in at least one microorganism of interest, comprising the following steps:

illuminating a sample containing microorganisms;

acquiring a total diffraction pattern of the sample, the total diffraction pattern comprising a plurality of unit diffraction patterns each associated with a microorganism, wherein each unit diffraction pattern comprises a center zone surrounded by concentric rings centered on the center zone;

determining a value of a numerical indicator (In) representative of a dispersion of the light intensity in a zone of interest of the total diffraction pattern, said zone of interest comprising at least one unit diffraction pattern, and each unit diffraction pattern of the zone of interest being associated with a microorganism known as the at least one microorganism of interest; and

reading calibration data relating a value of a numerical indicator (In) and a concentration (C) of lipids in the at least one microorganism of interest, for determining a concentration of lipids (C x ) in the at least one microorganism of interest.

2. The method according to claim 1 , wherein the zone of interest is defined to comprise a single unit diffraction pattern.

3. The method according to claim 1 , wherein the zone of interest is defined to comprise a plurality of unit diffraction patterns, and in that a mean concentration of lipids in the at least one microorganism of interest is determined.

4. The method according to claim 1 , wherein the numerical indicator (In) is a standard deviation of the light intensity in a zone of interest of the total diffraction pattern relative to a reference light intensity.

5. The method according to claim 1 , wherein the numerical indicator (In) is, for each unit diffraction pattern, a difference between the light intensity in the center of said unit diffraction pattern and the light intensity of a first dark ring thereof.

6. The method according to claim 1 , which is conducted in an in situ follow up of a culture of microorganisms in a pool or a bioreactor.

7. The method according to claim 1 , wherein the at least one microorganism of interest is at least one micro-alga.

8. A device configured to determine a concentration of lipids in at least one microorganism of interest, comprising:

a light source, arranged to illuminate a sample comprising microorganisms; and

a matrix photodetector disposed facing the light source, arranged to acquire a total diffraction pattern ( 12 ) of the sample, the total diffraction pattern comprising several unit diffraction patterns each associated with a microorganism; characterized by calculating means receiving as an input the total diffraction pattern, said calculating means comprising:

means for determining a value of a numerical indicator (In) representative of a dispersion of the light intensity in a zone of interest of the total diffraction pattern, said zone of interest comprising at least one unit diffraction pattern, and each unit diffraction pattern of the zone of interest being associated with a microorganism known as the at least one microorganism of interest, wherein each unit diffraction pattern comprises a center zone surrounded by concentric rims centered on the center zone;

means for reading calibration data relating a value of a numerical indicator (In) and a concentration (C) of lipids in the at least one microorganism of interest, for outputting a concentration of lipids (C x ) in the at least one microorganism of interest.

9. The device according to claim 8 , further comprising:

a first sealed housing, receiving the light source and having a first transparent window between the light source and the matrix photodetector;

a second sealed housing, receiving the matrix photodetector, and having a second transparent window between the first transparent window and the matrix photodetector;

the first sealed housing, the light source, the second sealed housing and the matrix photodetector forming together an immersible probe.

10. The device according to claim 8 , wherein the at least one microorganism of interest is at least one micro-alga.