Role of external calcium in homeostasis of intracellular pH in the cyanobacterium Anabaena sp. strain PCC7120 exposed to low pH

Understanding How Microorganisms Respond to Acid pH Is Central to Their Control and Successful Exploitation

Microbes from the three domains of life, Bacteria, Archaea, and Eukarya, share the need to sense and respond to changes in the external and internal concentrations of protons. When the proton concentration is high, acidic conditions prevail and cells must respond appropriately to ensure that macromolecules and metabolic processes are sufficiently protected to sustain life. While, we have learned much in recent decades about the mechanisms that microbes use to cope with acid, including the unique challenges presented by organic acids, there is still much to be gained from developing a deeper understanding of the effects and responses to acid in microbes. In this perspective article, we survey the key molecular mechanisms known to be important for microbial survival during acid stress and discuss how this knowledge might be relevant to microbe-based applications and processes that are consequential for humans. We discuss the research approaches that have been taken to investigate the problem and highlight promising new avenues. We discuss the influence of acid on pathogens during the course of infections and highlight the potential of using organic acids in treatments for some types of infection. We explore the influence of acid stress on photosynthetic microbes, and on biotechnological and industrial processes, including those needed to produce organic acids. We highlight the importance of understanding acid stress in controlling spoilage and pathogenic microbes in the food chain. Finally, we invite colleagues with an interest in microbial responses to low pH to participate in the EU-funded COST Action network called EuroMicropH and contribute to a comprehensive database of literature on this topic that we are making publicly available.

Demarcating antioxidant response against aluminum induced oxidative stress in Westiellopsis prolifica Janet 1941

Aluminum metal pollution is considered as a primary limiting factor that reduced crop yield in South Asian subtropical country like India. In national context, Odisha contributes around more than 40% of total ore availability. Moreover, industrial mining and smelting aid are major concern for aluminum metal toxicity in territorial vicinity affecting the soil fertility, ecosystem and human health through food chain. The aluminum metal accumulation limits the soil fertility by antagonistic regulation of photosynthetic and nitrogen fixing microbiota. The increasing concern regarding aluminum pollution enterprise critical investigations for their bioremediation in contamination sites. In this notion, the current study was hypothesized to decrypt the rate limiting factors, their explicit mode of action and intracellular detoxification in a cyanobacterium, i.e., Westiellopsis prolifica isolated from ash pond of NALCO (National Aluminum Company Limited), Angul, Odisha. In the experimental setup, treatment with different concentrations of AlCl₃ (0-0.1 mM) was marked a decline in the growth of the strain due to the adverse regulation of photosynthetic pigments. However, the enforcement of catalase (CAT), ascorbate peroxidase (APX), superoxide dismutase (SOD), guaiacol peroxidase (GPX) and glutathione reductase (GR) was critical for sustaining strain viability under oxidative imbalance. The observation of an increase in the antioxidant enzyme and MDA content was evident to sustain strain viability under such oxidative imbalance. The outcome of the anticipated study was apparent to demonstrate a colossal interlink between Al mediated induction of oxidative stress and their cellular detoxification via intracellular antioxidant enzymes and removal of H₂O₂ accumulation in cyanobacterium, W. prolifica. Statement of novelty Aluminum metal toxicity renders growth of Westiellopsis prolifica via affecting photosynthesis associated pigments. Westiellopsis prolifica deploys antioxidant defense enzymes to combat against aluminum mediated oxidative upset. Intracellular antioxidant enzymes provoke cellular survival of Westiellopsis prolifica under excessive uptake of aluminum in contaminated habitats.

Influence of H+ and calcium ions on surface functional groups of Synechococcus PCC 7942 cells

The chemistry of the surface functional groups of picocyanobacteria Synechococcus PCC 7942 cells was examined as a function of H+ and calcium concentrations. Titration experiments, infrared spectroscopy, biosorption experiments, and chemical modeling were used to gain insight into the mechanisms of biosorption. The pKa and concentration of active sites on the cell wall were clarified with the aid of potentiometric titration. Modeling calculations and infrared spectra are consistent with pKa's values of 4.3, 5.2, 6.9, 9.1, and 10.0 and a total concentration of 7.8 x 10(-4) mol g(-1). Spectral analysis of an aqueous cellular suspension revealed a presence of carboxyl, amide, phosphate, hydroxyl, and carbohydrate moieties. Correspondence between spectral data and potentiometric titration curves supported the hypothesis that carboxylate groups and phosphodiester groups mediate calcium adsorption to bacterial cells. This process is strongly pH dependent. In the second part of the experimental work, Synechococcus cells were suspended in the presence of different calcium concentrations. Mechanistic modeling demonstrated that the calcium adsorption phenomenon can be described taking into account only two mechanisms: ion exchange and complexation.

Effects of UV and visible light on cyanobacteria at the cellular level

The effect of UV and visible light on cyanobacteria was determined at the cellular level by means of epifluorescence and confocal microscopy techniques. These methods allow the examination of light effects in spatial resolution. Series of measurements were performed to determine the effect of different light qualities and quantities on cyanobacteria. To analyze the effect of the light quality, samples of Anabaena and Scytonema sp. were exposed to intense blue, green or red light applied from the epifluorescence path of the microscope. The fluorescence of the phycobiliproteins was recorded by means of epifluorescence (excitation 550 nm, 20 nm half band width (HBW), emission above 635 nm) or by confocal microscopy (560 nm laser line). Upon exposure to blue or green light the cells showed an increase in fluorescence followed by a sudden and complete loss of fluorescence. Blue light was more effective (bleaching of phycobiliproteins within 45 min) than green light (bleaching within 120 min). Red light was not as effective, and bleaching of the cells took at least 24 h. Initially the cells showed an increase in fluorescence followed by fast bleaching of the fluorescence signal. Cells exposed to UV plus PAR were bleached within 60 min, while cells exposed to photosynthetically active radiation (PAR) only were totally bleached after about 120 min. FL-DHP (dihydropyridine) labeling was performed in two cyanobacteria, Anabaena sp. and Nostoc commune, to visualize L-type calcium channels. Both cyanobacterial strains showed a pronounced FL-DHP signal of the heterocysts and akinetes but only a weak signal from the vegetative cells. The results clearly indicate the presence of calcium channels in these cells. UV radiation decreased the amount of chlorophyll and phycocyanin as could be seen from a decline in the autofluorescence of the cells. In contrast, the FL-DHP signal was not affected by UV.

Use of recombinant aequorin to study calcium homeostasis and monitor calcium transients in response to heat and cold shock in cyanobacteria

We investigated the possibility of Ca(2+) signaling in cyanobacteria (blue-green algae) by measuring intracellular free Ca(2+) levels ([Ca(2+)](i)) in a recombinant strain of the nitrogen fixing cyanobacterium Anabaena strain sp. PCC7120, which constitutively expresses the Ca(2+)-binding photoprotein apoaequorin. The homeostasis of intracellular Ca(2+) in response to increasing external Ca(2+) has been studied in this strain. The resting level of free Ca(2+) in Anabaena was found to be between 100 and 200 nM. Additions of increasing concentrations of external Ca(2+) gave a transient burst of [Ca(2+)](i) followed by a very quick decline, reaching a plateau within seconds that brought the level of [Ca(2+)](i) back to the resting value. These results indicate that Anabaena strain sp. PCC7120 is able to regulate its internal Ca(2+) levels. We also monitored Ca(2+) transients in our recombinant strain in response to heat and cold shock. The cell's response to both stresses was dependent on the way they were induced. The use of inhibitors suggests that heat shock mobilizes cytosolic Ca(2+) from both intracellular and extracellular sources, while the Ca(2+) source for cold shock signaling is mostly extracellular.