A comparison of proline, thiol levels and GAPDH activity in cyanobacteria of different origins facing temperature-stress

Abstract

Three cyanobacterial strains originating from different habitats were subjected to temperature shift exposures and monitored for levels of proline, thiol and activity of glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Thermophile Mastigocladus laminosus (growth optimum, 40 °C), raised the proline level 4.2-fold at low temperature (20 °C), for the psychrophile Nostoc 593 (growth optimum, 20 °C), it was raised 8-fold at 40 °C while in the mesophile Nostoc muscorum (growth optimum, 30 °C), the imino acid level increased 2.3-fold during temperature ‘shiftdown’ to 20 °C or 3.5-fold in sets facing ‘shiftup’ (40 °C). Alterations in thiol levels in the above strains were in line with proline. It is suggested that such fluctuations reflect metabolic shifts as a response to stress. Interestingly, GAPDH activity was maximum at the respective growth temperature optimum of M. laminosus (122 nmol NADPH oxidized min ⁻¹ mg ⁻¹ protein) and Nostoc 593 (141 nmol NADPH oxidized min ⁻¹ mg ⁻¹ protein) while in N. muscorum, it increased at 40 °C (101 nmol NADPH oxidized min ⁻¹ mg ⁻¹ protein) and to 93.3 nmol NADPH oxidized min ⁻¹ mg ⁻¹ protein (20 °C) relative to 86 nmol NADPH oxidized min ⁻¹ mg ⁻¹ protein at 30 °C. It seems that extremophiles maintain the GAPDH activity/level during growth at their respective temperatures optimal while the mesophile increases it in order to cope up with temperature-stress.