Dormancy of cells and organisms – strategies for survival and preservation

Cyanobacteria Dormancy Forms in an Aquatic environment

AKINETES

• What are they?• Their ecological role• Formation• Photosynthesis• Germination

Akinetes (from the Greek ` akinetos', meaning motionless) are differentiated thick- walled, resting cells produced by many strains of subsections IV (order Nostocales) and V (order Stigonematales), usually as cultures approach stationary phase.

They do not resemble the endospore structurally. They and are not heat resistant, but resist to cold and desiccation. They are larger than vegetative cells and have thickened extra cellular envelope

Akinetes contain higher amounts of storage compounds: glycogen & proteins (cyanophycin) and maintain low level of metabolic activities

Phosphate deficiency, specific light conditions, UV, simple organic carbon source and un-aerated conditions induce the formation of akinetes

Akinetes - Cyanobacteria Dormancy Forms What are they?

Aakinetes maintain residual metabolic activities as shown by incorporation of 35S into protein and lipid. They consumed 02 in the dark and evolved 02 in the light

Essentially every vegetative cell in the filament can differentiate into an Akinete

Akinetes germinate to produce new filaments under suitable conditions

Akinetes provide cyanobacteria with a means of over-wintering and surviving dry periods

Akinetes - Cyanobacteria Dormancy Forms

The ecological role of Akinetes

Schematic summary of the cyanobacteria life cycle (prototype for species of the order Nostocales)

From: Hense I & Beckmann A (2006) Ecological Modelling (in press)

Development and maturation of Akinetes of Aphanizomenon ovalisporum

Australian strain of Aphanizomenon ovalisporum was kindly provided by Lindsay Hunt, Queensland Health Scientific Services.

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Development and maturation of Akinetes of Aphanizomenon ovalisporum

Young akinetes perform photosynthetic activity at a similar rate as their adjacent vegetative cells

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Photosynthetic parameters derived from Microscope-PAM measurements

Despite measurable F0 values, only residual Fv was detected with photosynthetic yields ranging between 0.05 and 0.1

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Akinetes on filaments

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Akinetes on filament of

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rETRmax 120.0 2.9 39.6 1.9 28.3 1.3

Initial slope () 0.241 0.010 0.237 0.028 0.225 0.030

Ik 345 115 87

R2 0.994 0.962 0.956

Photosynthetic yield of Aphanizomenon vegetative cells and akinetes

Sample Vegetative Cells Akinetes

Control exponentially grown culture 0.575 0.057 N/A

Akinete-induced culture   

6 days 0.553 0.026 0.560 0.036

12 days 0.550 0.034 0.403 0.170

20 days 0.417 0.068 0.370 0.050

28 days 0.316 0.051 0.212 0.062

Isolated akinetes 6 weeks N/A 0.067 0.035

Maximal Photosynthetic quantum yield of vegetative cells and akinetes of Aphanizomenon ovalisporum measured by Microscope-PAM. Measured samples were vegetative cells in exponentially grown cultures, vegetative cells and akinetes in akinete induced cultures and akinets isolated from 6 weeks old akinete-induced culture.

Fluorescence emission spectra and their de-convoluted component bands of Aphanizomenon ovalisporum Akinetes and vegetative cells

Fluorescence emission spectra were measured with excitation at 435 nm

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Parameters of the component bands of fluorescence spectra at 77K of A. ovalisporum. Data was extracted from steady-state fluorescence emission spectra and their de-convoluted component bands.

Fluorescence emission spectra were measured with excitation at 440nm.

Band No ID

Exponentially grown culture Isolated Akinetes

peak (nm)

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Area (%)

peak (nm)

Hight (rel.)

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Area (%)

1 PC 649 0.022 13 4.2 651 0.139 20 37.1

2 APC 661 0.042 9 5.8 663 0.063 10 8.3

3 Core Antenna (F685) 684 0.056 7 6.4 685 0.051 6 3.9

4 PSII (F695) 694 0.095 12 17.9 693 0.066 10 9.1

5 PSI (FPSI) 720 0.172 21 56.9 721 0.158 19 41.2

6 Vibration 736 0.029 20 8.8 731 0.005 5 0.3

Characteristics of the component bands originated from PSII (F685 and F695) and PSI (FPSI) of fluorescence spectra at 77 K

a) The values were expressed as percentage relative to the sum of three emission bands (F685+F695+FPSI)

b) PSI/PSII fluorescence ratio is calculated from FPSI/F695

Cell typeF685

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(relative Area)

Vegetative 7.8 22.1 70.1 2.3

Akinetes 7.2 16.7 76.1 3.2

Abandance of cellular proteins (A) and Immuno-identification of PSII and PSI polypeptides (B) in isolated akinetes (1) and exponentially grown culture (2) of Aphanizomenon

In vivo fluorescence of Aphanizomenon akinetes

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In vivo fluorescence of Aphanizomenon: characterization by confocal laser scanning microscopy

Fluorescence was excited with the 488 nm line of Kr-Ar laser of a Leica TCS- SP5

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induced030 Movie.wmv

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In vivo fluorescence of Aphanizomenon: characterization by confocal laser scanning microscopy

Fluorescence was excited with the 488 nm line of Kr-Ar laser of a Leica TCS- SP5

Akinete induced culture 2 weeks old

akinete005 Movie.wmv

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In vivo fluorescence of Aphanizomenon: characterization by confocal laser scanning microscopy

Fluorescence was excited with the 488 nm line of Kr-Ar laser of a Leica TCS- SP5

Isolated akinetes (from 6 weeks old culture)

Summary

K deficiency triggers akinete formation in a yet unexplained process.

Young akinetes maintain photosynthetic capacity at a similar manner as found for their adjacent vegetative cells in filaments grown in akinete-inducing medium.

Mature akinetes maintain residual photosynthetic activity.

Some components of the photosynthetic apparatus appear to remain intact in akinetes.

In mature akinetes PSI and PSII complexes are kept apparently at a slightly higher molar ratio then in vegetative young cells (less PSII).

The phycobilisome pool is reduced in akinetes and disattached from the core antenna complexes.

Akinetes differentiation dormancy and germination – many processes are yet to reveal

From: Hense I & Beckmann A (2006) Ecological Modelling (in press)

Sensing & signal transduction

Development &maturation

Dormancy & reduced metabolism Sensing, signal

transduction & regulation

of germination

Collaborators and students

Prof John Beardall, Monash UniversitySven InhkenDiti Viner MuziniBina Kaplan Ruth Kaplan-LeviMerva Hadari

Apha. akinets formation in BG - K2HPO4 under different light intensities

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Formation of akinetes

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Apha. Akinetes in BG-K2HPO4 with and without 0.2mM KCl

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Formation of akinetes

Akinetes of Nostoc spongiaeforme and Nostoc punctiforme remain viable and do not germinate in distilled water, unless transferred to cyanobacterial growth medium (Huber 1985).

Non-germinating akinetes maintain residual metabolic activities as shown by incorporation of 35S into protein and lipid. They consumed 02 in the dark and evolved 02 in the light (Thiel & Wolk, 1983).

The composition of the external akinete polysaccharide layer has a structure similar to that found in the heterocysts

Cyanophycin is a nitrogenous reserve material abundant in akinetes (Herdman, 1987) .

Akinetes have increased resistance to environmental stress of desiccation, cold and lysozyme treatment as compared to vegetative cells.

Physiological features of akinetes – literature survey

P limiting conditions induce the formation of akinetes in Aphanizomenon

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Formation of akinetes