Rapid determination of the dry weight of single, living cyanobacterial cells using the Mach-Zehnder double-beam interference microscope

Figures & data

Fig. 1. Phormidium sp. in the monochromatic (λ = 546 nm) stripe field of the Leitz Dualbeam microinterferometer. The optical path difference (OPD) caused by the object leads to a curvature in the interference stripe. The distance between the undisturbed stripes is the direct measure of the OPD and can be read out directly from the image.

Fig. 2. (A) Determination of OPD by phase-stepping algorithm. This method is suitable for coloured or complex objects like Gloeocapsa. The bright field image shows that the algae have a green colour due to chlorophyll content, so the specific interference colour of the cell in the homogenous field is a mixture in the chlorophyll specific colour. By shifting the overall phase between reference and object wave in four different positions, which differ by a quarter of a wavelength or π/2 (where 2π is a full wavelength) the OPD distribution in the image plane can be calculated by a phase stepping algorithm (Schwider, 1983). (B) The result is a false coloured picture, in which OPD can be determined.

Table 1.  Trichome and cell sizes (diameter) of eight cyanobacterial species – comparison of two methods.

	Digital images, pixel number, stage micrometer			Direct microscopic measurements, eyepiece graticule, stage micrometer
	Average d ± SD		n	Average d ± SD		n
Species	µm	%		µm	%
Anabaena c.f. thermalis	2.98	28.9	4	3.22	23.6	10
Calothrix parietina: Base	12.78	11.85	2	12.50	11.00	2
Middle	9.62	7.40	2	9.43	5.6	7
Cylindrospermum muscicola	3.97	8.6	6	3.67	6.8	10
Gloeocapsa sp.: Cell	5.25	12.2	40	5.30	7.0	10
Leptolyngbya foveolarum (a)	1.98	7.1	6	nd
Leptolyngbya foveolarum (b)	3.18	4.7	3	nd
Mean of (a) and (b)	2.38	25.6	9	2.61	11.5	10
Oscillatoria cf. rupicola	6.29	6.2	10	6.30	5.1	10
Phormidium autumnale	5.81	8.6	11	5.76	4.5	10
Spirulina platensis	11.63	3.6	4	11.02	9.1	10
nd: not determined.

Fig. 3. Parameters related to coenobial diameters of Gloecapsa spec. Points represent single coenobia. (a) Cell numbers of single coenobia; (b) dry weight ratio mucous material per cell; (c) the total (cells and mucilage) dry weight of the coenobia.

Table 2.  The optical path difference (OPD) of eight cyanobacterial species in relation to the means of trichome and cell diameters.

	Average d	Average OPD
Species	µm	nm	±SD	n
Anabaena c.f. thermalis	2.98	111.10	26.04	4
Calothrix parietina: Basis	12.31	690.81	–	2
Middle	8.51	376.40	–	2
Cylindrospermum muscicola	3.97	129.76	11.63	6
Gloeocapsa sp.: Cell	5.25	281.10	68.79	13
Leptolyngbya foveolarum (a)	1.98	99.94	7.90	6
Leptolyngbya foveolarum (b)	3.18	178.91	21.89	3
Mean of (a) and (b)	6.29	277.76	28.80	10
Oscillatoria cf. rupicola	5.46	26.44	6.76	11
Phormidium autumnale	5.81	246.84	9.30	11
Spirulina platensis	11.63	437.81	159.44	4

Table 3.  Mean values of the dry weight per unit biovolume of eight cyanobacterial species, calculated from OPD and size measurements; min–max values are from single cells and trichomes respectively.

	Dry mass/unit biovolume (fg µm^−3)
Species	Average	±SD	Measured min–max	n
Anabaena cf. thermalis	230.9	73.6	(161.4–325.8)	4
Calothrix parietina: Base	331.2	–	(302.4–360.0)	2
Middle	258.4	–	(244.4–272.4)	2
Cylindrospermum muscicola	192.6	15.4	(175.0–218.4)	6
Gloeocapsa sp.: Cell	143.5	41.2	(70.0–210.0)	13
Leptolyngbya foveolarum (a)	319.7	67.1	(248.3–459.2)	13
Leptolyngbya foveolarum (b)	298.2	34.7	(237.9–332.4)	6
Mean of (a) and (b)	329.8	25.8	(300.2–346.5)	3
Oscillatoria cf. rupicola	261.4	36.9	(190.8–314.5)	10
Phormidium autumnale: sheath	28.4	6.9	(20.0–40.1)	11
Phormidium autumnale	251.6	23.5	(202.9–401.2)	11
Spirulina platensis	217.2	83.6	(131.7–327.7)	4

Table 4.  Carbon content of 8 cyanobacterial species as a percentage of dry mass.

	Carbon (% of dry mass)
Species	Average	±SD	n
Anabaena cf. thermalis	51.47	1.75	6
Leptolyngbya foveolarum	46.69	2.13	7
Oscillatoria cf. rupicola	49.45	0.35	5
Phormidium autumnale	49.99	1.48	17
Spirulina platensis	42.99	1.51	6

Table 5.  Dry weight per unit biovolume of six cyanobacterial species calculated by different authors.

	Dry mass/unit biovolume
Species	fg µm^−3	Min–max	Reference
Anabaena circinalis	454.4	436.2–490.0	Reynolds (1984)
Aphanizomenon flos-aquae	466.7	457.1–475.6	Reynolds (1984)
A. flos aquae f. gracile	350.0	nd	Jörgensen (1979)
Oscillatoria agardhii var. isothrix	600.9	339.1–1957	Reynolds (1984)
Oscillatoria agardhii var. isothrix	425.0	nd	Jörgensen (1979)
Oscillatoria bourrellyi	620.0	nd	Jörgensen (1979)
Microcystis aeruginosa	438.4	419.0–442.3	Reynolds (1984)
Synechococcus sp.	530.0	440–620	Stramski (1999)
Dry weight calculated as carbon = 50% of dry mass. nd: no data.

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