Soil pH is probably the single most informative measurement that can be made to determine soil characteristics. At a single glance, pH tells much more about a soil than merely indicating whether it is acidic or basic. For example, availability of essential nutrients and toxicity of other elements can be estimated because of their known relationship with pH. The term pH was "invented" by the Swedish scientist Sorensen (1909) in order to obtain more convenient numbers and the idea quickly caught on. Gillespie and Hurst (1918) seem to have been among the earliest to determine pH (or PH, as it was then called) electrometrically using a platinum-palladium blackhydrogen gas electrode, a calomel reference electrode and a fairly cumbersome potentiometer and galvanometer system. At that period, it was still much more common to use colorimetric methods with indicator dyes than the electrometric method. This changed rapidly, however. Sharp and Hoagland (1919) used a similar but less involved method than Gillespie and Hurst (1918) and Healy and Karraker (1922) used a commercially available platinum-hydrogen gas electrode, potentiometer and galvanometer which had been designed by Clark (1920). The decade of the 1920s saw the development of the quinhydrone electrode which was less fragile and much less expensive than the hydrogen-platinum electrode. But, it was the development of the glass electrode in the 1930s that brought the determination of pH very rapidly to its present importance and convenience. The Beckman Model G pH meter (circa 1931) was practically indestructible and could be used as a portable as well as a laboratory instrument. Although it was cumbersome by today's standards, it was virtually foolproof (except for the constantly failing batteries) and many are still capable of operating if not actually operating today. As recently as two decades ago, the use of the small, handheld portable pH meters then available to determine pH in the field was a very imprecise and hazardous undertaking because both electrodes and meters were subject to sudden failures but this has changed rather abruptly in the last few years. Microcircuitry and plastic have contributed to rugged pH meters and electrodes that withstand
Nucleic acid amplification is the basis for many molecular diagnostic assays. In these cases, the amplification product must be detected and analyzed, typically requiring extended workflow time, sophisticated equipment, or both. Here we present a novel method of amplification detection that harnesses the pH change resulting from amplification reactions performed with minimal buffering capacity. In loop-mediated isothermal amplification (LAMP) reactions, we achieved rapid (<30 min) and sensitive (<10 copies) visual detection using pH-sensitive dyes. Additionally, the detection can be performed in real time, enabling high-throughput or quantitative applications. We also demonstrate this visual detection for another isothermal amplification method (strand-displacement amplification), PCR, and reverse transcription LAMP (RT-LAMP) detection of RNA. The colorimetric detection of amplification presented here represents a generally applicable approach for visual detection of nucleic acid amplification, enabling molecular diagnostic tests to be analyzed immediately without the need for specialized and expensive instrumentation.
Continent-scale biogeography has been extensively studied in soils and marine systems, but little is known about biogeographical patterns in non-marine sediments. We used barcode pyrosequencing to quantify the effects of local geochemical properties and geographic distance for bacterial community structure and membership, using sediment samples from 15 lakes on the Tibetan Plateau (4–1670 km apart). Bacterial communities were surprisingly diverse, and distinct from soil communities. Four of 26 phyla detected were dominant: Proteobacteria, Bacteroidetes, Firmicutes and Actinobacteria, albeit 20.2% of sequences were unclassified at the phylum level. As previously observed in acidic soil, pH was the dominant factor influencing alkaline sediment community structure, phylotype richness and phylogenetic diversity. In contrast, archaeal communities were less affected by pH. More geographically distant sites had more dissimilar communities (r = 0.443, P = 0.030). Variance partitioning analysis showed that geographic distance (historical contingencies) contributed more to bacterial community variation (12.2%) than any other factor, although the environmental factors explained more variance when combined (28.9%). Together, our results show that pH is the best predictor of bacterial community structure in alkaline sediments, and confirm that both geographic distance and chemical factors govern bacterial biogeography in lake sediments.
Mostafa M. S. Ismaiel, Y. El-Ayouty, M. Piercey-Normore
Algae can tolerate a broad range of growing conditions but extreme conditions may lead to the generation of highly dangerous reactive oxygen species (ROS), which may cause the deterioration of cell metabolism and damage cellular components. The antioxidants produced by algae alleviate the harmful effects of ROS. While the enhancement of antioxidant production in blue green algae under stress has been reported, the antioxidant response to changes in pH levels requires further investigation. This study presents the effect of pH changes on the antioxidant activity and productivity of the blue green alga Spirulina (Arthrospira) platensis. The algal dry weight (DW) was greatly enhanced at pH 9.0. The highest content of chlorophyll a and carotenoids (10.6 and 2.4 mg/g DW, respectively) was recorded at pH 8.5. The highest phenolic content (12.1 mg gallic acid equivalent (GAE)/g DW) was recorded at pH 9.5. The maximum production of total phycobiliprotein (159 mg/g DW) was obtained at pH 9.0. The antioxidant activities of radical scavenging activity, reducing power and chelating activity were highest at pH 9.0 with an increase of 567, 250 and 206% compared to the positive control, respectively. Variation in the activity of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) was also reported. While the high alkaline pH may favor the overproduction of antioxidants, normal cell metabolism and membrane function is unaffected, as shown by growth and chlorophyll content, which suggests that these conditions are suitable for further studies on the harvest of antioxidants from S. platensis.
The relationship between broiler breast meat color and pH, moisture content, water-holding capacity (WHC), and emulsification capacity (EC) was investigated. In each of three replicate trials, fillets were collected from three different commercial processing plants according to breast meat lightness (L*) values as follows: lighter than normal (light, L* > 53), normal (48 < L* < 53), and darker than normal (dark, L* < 46). Color values of lightness (L*), redness (a*), and yellowness (b*) were measured at 0 and 24 h after collection. Fillets were then ground and homogenized prior to determining color, pH, moisture, WHC, and EC of the ground meat. There was a significant difference among the three color groups (light, normal, and dark) in L*, a*, pH, WHC, and EC. The L* values of whole raw breast fillets had significant negative correlation coefficients with ground meat EC (-0.9237), pH (-0.9610), and a* (-0.6540). Emulsification capacity had significant positive correlations with pH (0.9572) and water-holding capacity (0.7080). WHC had significant correlations with a* (0.8143), moisture (-0.7647), and pH (0.7963). Lighter-than-normal meat was associated with low pH, high moisture, low EC, and low WHC. These results indicate that wide differences in raw breast meat color exist and that these differences may be used by poultry further processors as an indicator of fillets with altered functional properties.