Rapid transient growth at low pH in the cyanobacterium Synechococcus sp

Abstract

The thermophilic cyanobacterium Synechococcus sp. strain Y-7c-s grows at its maximum rate at a high pH (pH 8 and above) and does not show sustained growth below pH 6.5. However, rapidly growing, exponential-phase cells from high-pH cultures continued to grow rapidly for several hours after transfer to pH 6.0 or 5.0. This transient growth represented increases in mass and protein, but cells failed to complete division. Viability loss commenced well before the cessation of growth, and cells at pH 5.0 showed no net DNA synthesis. When irradiated by visible light, cells at pH 6.0 and 5.0 maintained an internal pH of 6.9 to 7.1 (determined by 31P nuclear magnetic resonance spectroscopy) and an extremely high ATP/(ATP + ADP) ratio even after growth had ceased. Cells exposed to a low pH did not show an increase in the spontaneous mutation rate, as measured by mutation to streptomycin resistance. However, cells already resistant to streptomycin were more resistant to viability loss at a low pH than the parental type. Cultures that could grow transiently at a low pH had higher rates of viability loss than nongrowing cultures in light or darkness. The retention of a high internal pH by cells exposed to a low pH suggested that a low pH acted initially on the cell membrane, possibly on solute transport.

BISULPHITE‐INDUCED PIGMENT DAMAGE IN THE BLUE‐GREEN ALGA NOSTOC CALCICOLA BRÉB.

“…Chlorophylls are known to be converted to phaeophytins as a consequence of exposure to weak acids by replacement of Mg^"^ with two atoms of hydrogen, thereby changing the spectral properties (Rao & LeBlanc, 1966), and this spectral shift could be taken as a useful parameter of SOg pollution. Phaeophytinization has also been reported in blue-green algal cells exposed to low pH conditions (Kallas & Castenholz, 1982). Similar types of chlorophyll conversions have been reported in plants exposed to acids like hydrofluoric acid and hydrochloric acid (Arndt, 1971).…”

“…The spectral changes in chlorophylls following exposure to SOg reported earlier (Rao & LeBlanc, 1966), may be used as a valuable criterion to assess SO2 damage. Chlorophylls are also known to undergo phaeophytinization in blue-green algal cells exposed to low pH conditions (Kallas & Castenholz, 1982). Since the cyanophytes have, in addition to Chi a, two water-soluble accessory pigments (C-phycocyanin and C-phycoerythrin), it is of importance to investigate the fate of the latter under bisulphite-stress.…”

Proteomic characterization of acid stress response inSynechocystis sp. PCC 6803

“…These organisms have the potential to maintain the cytoplasmic pH near to neutrality, by different acid-resistant systems, even when they are exposed to extremely acidic conditions. In the cyanobacterium, Synechococcus, Kallas and Castenholz [7] also noticed a high intracellular pH near 7.0 when cells were transferred to mild but growth-limiting levels of acidity. Interestingly, in the present study, the quintessential marker of bacterial stress response, the DnaK protein (prokaryotic hsp 70 family protein), and other stress proteins such as 60-kDa chaperonin 1 and 2 [32], did not show significant change in their expression levels.…”

“…Proteomic analysis of acid stress response in Synechocystis, with a special focus on the pH-dependent expression of periplasmic proteins, allowed identification of several proteins whose expression levels changed in response to the external pH. Since in cyanobacteria a rapid but transient growth was already known to occur under acidic pH [7], instead of giving a short-term exposure to acidity, cells were grown in media adjusted to an acidic pH for few days and proteomic comparisons were made with cells grown at optimal pH. Therefore, it should be noted that results reported here do not represent the transient proteome changes due to pH shift, but rather allowed identification of stable protein changes, essential for long-term adaptation to acidity.…”

“…In an attempt to elucidate survival strategies and cytoplasmic pH homeostasis in cyanobacteria, Kallas and Castenholz [6] observed that growth rate of Synechococcus was inhibited at pH 7.0 and below, and no sustained growth took place at pH 6. However, even when these cells were exposed to pH 4.8, they retained a higher intracellular pH [7], thereby suggesting that apart from pH homeostasis, there are other plausible factors involved in the acid limited physiology of these photosynthetic microbes.…”