Variations in the microcystins production of Planktothrix rubescens assessed from a four years survey of Lac du Bourget (France) and from laboratory experiments Briand J.-F.1,2, Jacquet S.1, Flinois C.3, Avois-Jacquet C.1, Maisonnette C.1,3, Leberre B.1, & Humbert J.-F.1
1
UMR CARRTEL, INRA, Equipe de Microbiologie Aquatique, Thonon-les-Bains
2 Laboratoire 3
des Sciences de l’Eau et de l’Environnement, Université Limoges
Laboratoire Environnement et Chimie Analytique, CNRS ERS 657, ESPCI, Paris
Lac du Bourget (Savoy, France) ! Largest natural French lake ! On the edge of the Alps (231m) ! Used as drinking water supply
B 145 m depth
Lac du Bourget Rhône river 3 km
18 km
P. rubescens distribution and dynamics
(in situ Fluoroprobe)
70000
Cell.mL
65000
60000
55000
50000
45000
40000
35000
30000
25000
20000
15000
10000
5000
0
Depth (m)
-1
0
50
July 1999
July 2000
July 2001
July 2002
Microcystins produced by P. rubescens
(LC-ESI-MS)
[D-Asp3]
MC-RR
[D-Asp3, Dhb7] MC-RR
[D-Asp3] MC-LR
Absorbance (AU)
0,004
0,003
0,002
0,001
0
Time (min) 5
10
15
20
25
Annual variations of P.rubescens MC conc. in Lac du Bourget ! max. between Aug. and Nov., up to 6.7 µg.L-1 ! [D-Asp3] MC-RR
+ [D-Asp3, Dhb7] MC-RR
= 93%
! main variant = [D-Asp3, Dhb7] MC-RR (55 to 100%) 3
! no influence of depth or period on the relative ratio
2
1
0 08 11 / 99 / 02 99 / 05 00 /0 08 0 /0 11 0 /0 02 0 /0 05 1 /0 08 1 11 / 01 02 / 01 / 05 02 /0 08 2 / 11 02 /0 2
MCs (LR eq., µg . L-1)
4
(10 m depth)
What about the relationship between MC concentrations and P. rubescens cell densities ? ! ever higher when cyanobacteria are stratifed in the metalimnion
Cell . mL -1
80000
Cell . mL
-1
80000 60000
60000
[D-Asp3] MC-RR
40000
(LR eq., µgL-1)
20000
(r2= 0.84, n=34, p
