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For mass culture of photosynthetic green microalgae, industrial flue gases can represent a low-cost resource of CO2. However, flue gases are often avoided, because they often also contain high levels of SO2 and/or NO2, which cause significant acidification of media to below pH 3 due to production of sulfuric and nitric acid. This creates an unsuitable environment for the neutrophilic microalgae commonly used in large-scale commercial production. To address this issue, we have looked at selecting acid-tolerant microalgae via growth at pH 2.5 carried out with samples bioprospected from an active smelter site. Of the eight wild samples collected, one consisting mainly of Coccomyxa sp. grew at pH 2.5 and achieved a density of 640 mg L−1. Furthermore, three previously bioprospected green microalgae from acidic waters (pH 3–4.5) near abandoned mine sites were also re-acclimated down to their in-situ pH environment after approximately 4 years spent at neutral pH. Of those three, an axenic culture of Coccomyxa sp. was the most successful at re-acclimating and achieved the highest density of 293.1 mg L−1 and maximum daily productivity of 38.8 mg L−1 day−1 at pH 3. Re-acclimation of acid-tolerant species is, therefore, achievable when directly placed at their original pH, but gradual reduction in pH is recommended to give the cells time to acclimate.

Soil pH conditions have important consequences for microbial community structure, their dynamics, ecosystem processes, and interactions with plants. Low soil pH affects the growth and functional activity of bacterial biocontrol agents which may experience a paradigm shift in their ability to act antagonistically against fungal phytopathogens. In this study, the antifungal activity of an acid tolerant soil bacterium Bacillus amyloliquefaciens MBNC was evaluated under low pH and compared to its activity in neutral pH conditions. Bacterial supernatant from three-day old culture grown in low pH conditions were more effective against fungal pathogens. B. amyloliquefaciens MBNC harboured genes involved in the synthesis of secondary metabolites of which surfactin homologues, with varying chain length (C11 – C15) were identified through High-Resolution Mass Spectroscopy. The pH of the medium influenced the production of these metabolites. Surfactin C15 was exclusive to the extract of pH 4.5; production of iturinA and surfactin C11 was detected only in pH 7.0 while, surfactin C12, C13 and C14 were detected in extracts of both the pH conditions. The secretion of phytohormones viz. Indole Acetic Acid (IAA) and Gibberellic Acid (GA) by B. amyloliquefaciens MBNC were detected in higher amount in neutral condition compared to acidic condition. Although, secretion of metabolites and phytohormones in B. amyloliquefaciens MBNC was influenced by the pH condition of the medium, the isolate retained its antagonistic efficiency against several fungal phyto-pathogens under acidic condition.

The use of CO2 rich industrial flue gases to support cultivation of microalgae to produce lipids for biofuel and other applications is an increasingly researched option. However, this approach presents a challenge, as whilst flue gasses typically contain 6-10% CO2, excessive medium acidification can be caused by the presence of NOx and SO2. The use of acidophilic or acid-tolerant species is a possible solution, but little is known about these microalgae. In this study we investigated the growth of a bioprospected acid-tolerant mixed photosynthetic green microalgae culture (91% dominated by a single Coccomyxa sp. taxon) at pH 2.5 and fed with a simulated flue gas containing 6% CO2 and 94% N2. At the end of the exponential growth phase, lipid accumulation and profiles, and the elemental composition of biomass were analysed over one week during which biomass was exposed to either continued light-dark cycle conditions or continual dark conditions. After three days of dark stress, the biomass consisted of approximately 28% of lipids, which was 42% higher than at the end of the exponential phase and 55% higher than the maximum lipid content achieved under light/dark conditions. Oleic acid (C18:1), pentadecanoic acid (C15:0), and palmitic acid (C16:0) were the dominant fatty acids at the end of the exponential phase, and light-dark and dark-treated biomass, respectively. Dark stress conditions favoured polyunsaturated fatty acid production and showed an increase in nitrogen content. This suggests that the use of dark stress to stimulate production of desirable lipids is a no-cost alternative to other commonly used stressors.

Thermoacidophilic Alicyclobacillus strains attract great interests as the resource of thermostable or acidic enzymes. In this study, a putative gene encoding superoxide dismutase (AaSOD) was identified in a thermoacidophilic Alicyclobacillus strain. With a 16-fold activity observed, the AaSOD activity expressing in the medium of manganese enrichment was much higher than that in the iron medium. In addition, the purified AaSOD can be reconstituted exclusively with either Fe2+ or Mn2+, with its Mn-bound protein showing 25-fold activity than that of Fe-bound form. The optimal temperature for AaSOD reaction was 35°C, and was highly stable at any certain temperature up to 80°C. Of particular interest, the enzyme is found to be very stable across a wide pH range spanning from 2.0 to 10.0, which confers its robust stability in the acidic stomach environment and implies striking potentials as food additive and for medical use.

The distribution, evolutionary relationships, and acid-resistance level (including mechanisms behind it) were studied in acid-tolerant chironomid species in Japan. All six species studied showed a tendency of restricted distribution. Chironomus acerbiphilus showed the highest acid tolerance with 50% survival at pH 0.75, whilst C. cf. riparius and C. solicitus showed the 2nd highest tolerance. Tolerance mechanisms, including enzymatic protein digestion into smaller molecules, was strongly observed, even at pH 2.0 in C. sulfurosus. Additionally, C. cf. riparius displayed the highest H+-ATPase activity; however, the same activity level was observed in both acid-tolerant and non-tolerant species. Phylogenetic analysis did not result in any exclusive acid-tolerant clades, although C. cf. riparius and C. solicitus formed an exclusive small clade within the genetic tree based on their cytochrome oxidase I (CO I) region. Other acid-tolerant species were grouped within clades with non-tolerant species. C. cf. riparius and C. solicitus, distributed only in northern Japan, were estimated to have diverged from ancestral species earlier, while C. fusciceps and C. sulfurosus, distributed only in southern Japan, diverged later. These results point to the possibility of Japanese acid-tolerant chironomids originating in northern area and later expanding their range to southern areas.

Microbiological spoilage of salad dressings and similar products generally results from the growth of a select group of microorganisms. Although frequently isolated these organisms have not been well characterized. Several isolates from spoiled products were examined. Data indicated that spoilage resulted from growth of lactobacilli, similar to the previously described Lactobacillus fructivorans , and yeasts, similar to Saccharomyces bailii . In addition to their acid tolerance, these organisms shared one other common characteristic, rapid fermentation of fructose. Addition of this carbohydrate to enumeration media resulted in improved recovery of both lactobacilli and yeasts.

Nitrification is an acidifying process that requires the addition of external alkalinity because of the alkaliphilic nature of the most ammonia-oxidizing bacteria. In this study, aerobic activated sludge was used as inoculum in an internal loop air-lift reactor, which resulted in successful enrichment of acid-tolerant nitrifying (ACIN) sludge at pH 6.0 by sequential addition of tea orchard soil suspension. The results showed that ACIN sludge had a remarkable acid tolerant capability with a volumetric ammonia conversion rate of 1.13 kg N m −3 day −1 . ACIN sludge showed a higher maximum specific ammonia conversion rate (0.29 g N g −1 VSS day −1 ) than neutrophilic nitrifying sludge (0.14 g N g −1 VSS day −1 ) at pH 6.0 and had good resistance against pH fluctuations, with a maximum specific ammonia conversion rate (0.584 g N g −1 VSS day −1 ) at pH 7.5. Microbial community analysis indicated that the higher abundance of acid tolerant Nitrosospira and ammonia-oxidizing archaea laid a solid foundation for the remarkable acid-tolerant capability of ACIN sludge.

This research presents a green procedure to prepare oil in water (O/W) emulsion from acid soluble soy protein (ASSP) and soy soluble polysaccharide (SSPS), a long-term stable nanoscale system for delivering the lipophilic components. The emulsion technique involved the preparation complexion using ASSP and SSPS by electrostatic and hydrophobic interactions as well as high pressure homogenization. The average diameter of the droplet of emulsions (fresh and heated) is 263±2nm. Such emulsions resulted in heating stable dispersions containing corn oil at the concentration of 20.0%, even at the pH around the isoelectric points of ASSP. After 90days storage at 4°C, the mean diameter of emulsions after heating at 80°C for 60min is 314±1nm compared with 341±3nm of emulsions unheated. The heat-stability of dispersions were affected by emulsion conditions, so the present research demonstrates the emulsion stability against heat treatment, ionic strength and pH change.

This study analyzed the lipid profiles of two acid-tolerant mutants (M1 and M5) and a wild-type (WT) strain of Chlorella saccharophila. Six main types of compounds were identified in the lipid fractions: hydrocarbons, FAMEs (after transesterification of TAGs), free fatty acids, terpenes, sterols and fatty alcohols. Compared with the M1 and M5 mutant lines, the WT strain presented the highest relative abundance of hydrocarbons (73.63%), while the relative abundance of fatty acid methyl esters (FAMEs) obtained were higher in the M1 (28.39%) and M5 (29.17%) mutants than in the WT strain. High-value lipids, including terpenes and fatty alcohols, were also detected in higher proportions in the M1 and M5 mutants than in the WT strain, while sterols were only detected in the M1 and M5 mutants. These results show that C. saccharophila and its acid-tolerant mutants are a rich source of lipids with potential industrial applications.

Here we report the draft genome sequence of the acid-tolerant Desulfovibrio sp. DV isolated from the sediments of a Pb-Zn mine tailings dam in the Chita region, Russia. The draft genome has a size of 4.9 Mb and encodes multiple K+-transporters and proton-consuming decarboxylases. The phylogenetic analysis based on concatenated ribosomal proteins revealed that strain DV clusters together with the acid-tolerant Desulfovibrio sp. TomC and Desulfovibrio magneticus. The draft genome sequence and annotation have been deposited at GenBank under the accession number MLBG00000000.

Purpose Large areas of land have been impacted by acidic mine drainage. These sites could potentially be re-vegetated for growing energy plants. Conventional phytoremediation method may fail because the pH of some mine drainage and contaminated soils can reach 2.0. Thus, it is necessary to screen acid-tolerant plants as pioneers to rehabilitate those severely acidified areas.

Seven non-pathogenic Escherichia coli strains: ATCC 25253, ATCC 25922, ATCC 11775, ATCC 8739, ATCC 11229, NAR and O157 Dm3Na were tested as potential candidates for the surrogate of pathogenic O157:H7 and non-O157 STEC strains (O111:NM, O26:H11, O145:NM and O103:H2) in apple juice treated by UV-C light. The survival studies in apple juice (pH 3.5) revealed that all non-O157 pathogens exhibit acid resistance similar to O157:H7. Subsequently the acid tolerant bacteria, i.e.: all STEC strains, ATCC 11229, ATCC 11775, ATCC 8739 and O157 Dm3Na, were exposed to three UV-C sources emitting light at the wavelengths of 222 nm, 254 nm and 282 nm. The inactivation studies of the nine most UV resistant strains indicated that ATCC 11229 strain can be recommended as a potential surrogate organism for UV treatments of non-O157 STEC strains at 222 nm. In the case of UV-C at 254 nm and 282 nm E. coli ATCC 8739 strain met the criteria for the surrogate organism for O157:H7 and non-O157 STEC strains. The manuscript presents the systematic procedure for the selection and verification of the potential surrogate organisms that can be recommended for validation of UV light processing of high acid juices and beverages.

Symbiosis of common bean with nitrogen-fixing bacteria can lead to a reduction in production costs and in environmental impacts. Considering the diversity of soils and climates, it is important to validate bacterial strains under different conditions to consolidate their recommendation as inoculants. Studies concerning the economic viability of Rhizobium inoculation in common bean are few, but they could assist in choosing the strain to be adopted. The aim of this study was to evaluate the performance of Rhizobium strains isolated from acid soils from the Amazon inoculated in seeds of the BRSMG Madrepérola cultivar and to evaluate the economic viability of their use in the field. Four field experiments were conducted in the state of Minas Gerais, Brazil. A randomized block experimental design was used with four replications and seven treatments: inoculation with the strains CIAT 899 (Rhizobium tropici), UFLA 02-100 (R. etli), UFLA 02-68 (R. etli bv. mimosae), UFLA 02-127 (R. leguminosarum bv. phaseoli), and UFLA 04-173 (R. miluonense),plus two controls, one without inoculation + mineral nitrogen (N-urea) at a rate of 80 kg N ha-1 and another without inoculation and without mineral N. The strain CIAT 899 is already recommended for the manufacture of a commercial inoculant, and the others, collected in the Amazon Forest, have proven to be highly effective in biological nitrogen fixation. Symbiosis of common bean with all the strains evaluated leads to satisfactory yields, with reduction in the application rate of mineral nitrogen and in environmental impacts and, consequently, reduction in economic costs, with higher profitability.

Here, we report the draft genome sequence of the acid-tolerant yeast Candida zemplinina NP2, which was isolated from peach peels. This genome sequence will aid in the understanding of the organism’s physiological properties as a potential producer of organic acids in acidic environments.

The ability of the freshwater alga, Chlorella kessleri, to maintain a carbon concentrating mechanism when grown at acid pH was investigated. The alga grows over the pH range 4.0-9.0 and was found to take up bicarbonate and CO2 actively when grown at pH 6.0. However, when grown at acid pH (below 5.5), it does not have active CO2 uptake. The acidotolerant species maintained an internal pH of 6.1-7.5 over the external pH range 4.5-7.5, thus the pH difference between the cell interior and the external medium was large enough to allow for the diffusive uptake of CO2 at acid external pH. Mass spectrometric monitoring of O2 and CO2 fluxes by suspensions of C. kessleri, grown at acid pH, and maintained at pH 7.5 showed that the rates of O2 evolution did not exceed those of CO2 uptake. The final CO2 compensation concentrations of 14.0-17.7 µM reached by photosynthetic cells were above the CO2 equilibrium concentration in the external medium, indicating a lack of active CO2 uptake at acid pH. Chlorella kessleri accumulated CO2 with internal concentrations that were 9.9, 18.7 and 22.7-fold that of the external medium for cells grown, respectively, at pH 4.5, 5.0 and 5.5. The ability of C. kessleri cells to accumulate high intracellular concentrations of inorganic carbon at acid pH would provide a sufficiently high concentration of CO2 at the active site of Rubisco thus allowing the alga to maintain growth rates similar to those at alkaline pH.

The occurrence of picocyanobacteria, the smallest cell-size fraction of cyanobacteria, in low-pH waters, is still poorly studied. In this study, we tested the hypothesis that picocyanobacteria found occasionally in low-pH environments are adapted to such water conditions. We isolated picocyanobacteria by means of the cytometric method from two humic lakes with pH ≤5. We obtained two strains belonging to two cosmopolitan phylogenetic clades of picocyanobacteria: Cyanobium gracile cluster and Subalpine cluster I. Experiments on filtered lake water from low-pH (≤5) and slightly alkaline (pH 8.2) lakes, and with an acidified cyanobacterium medium (pH 4.5) were conducted to test the growth of the isolated picocyanobacteria in various pH conditions. The experimental results of this study showed that some picocyanobacteria strains were acid tolerant, achieving higher growth rates and reaching higher maximum numbers in humic, naturally acidic waters rather than in alkaline waters. We show that despite a close phylogenetic relationship, strains of picocyanobacteria exhibit significant physiological and ecological diversity and that at least some picocyanobacteria have the evolutionary potential to cope with low pH. Characterization of the genetic basis of acid tolerance in picocyanobacteria is important to understand how these microorganisms function in aquatic ecosystems and how their communities may respond to a changing environment.

The Koch–Haaf reaction of adamantanols was successfully carried out in a microflow system at room temperature. By combining an acid-tolerant hastelloy-made micromixer, a PTFE tube, and a hastelloy-made microextraction unit, a packaged reaction-to-workup system was developed. By means of the present system, the multigram scale synthesis of 1-adamantanecarboxylic acid was achieved in ca. one hour operation.

Introduction Bioproduction of optically pure lactic acid (LA) has roused interest in the recent years due to its potential application in a wide range of fields, and there is a significant interest to further development of sustainable and cost-effective process. However, the efficient utilization of agro-industrial wastes for LA production still causes considerable challenges. The biotechnological LA production within the targeted cost still required the development of high-performance LA-producing microorganisms and the lowering of the costs of raw materials and fermentation process. Cheap biomass, such as starchy and cellulosic agricultural residues or by-products from the food industry, has a potential for the cost-effective production of LA, but raw materials also should have a high production rate and yield without by-product formation and the ability to be fermented with low pretreatment (Wee et al., 2006). Whereas the LA made by fermentation route refers optically active, consequently a suitable microorganism could selectively produce dextro (levo)-rotation enantiomers, and the greatest demand is for the l-LA isomer (Sheldon, 2011). Targeted conversion of starchy substrates to LA can be performed using the amylolytic microorganisms (Gonzalez et al., 2007). Fungi species from Rhizopus, such as Rhizopus oryzae and Rhizopus arrhizus, excreate amylolytic activity that enables to convert starch directly into l-LA in the presence of oxygen (Hofvendahl and Hahn-Hägerdal, 2000). However, LA-producing microorganisms, including the fungus R. oryzae, have low productivity depended on the low reaction rate caused by mass transfer limitation (Okano et al., 2010). Most of the world’s commercial l-LA is produced by the fermentation of carbohydrates using homolactic microbes such as a variety of modified or developed strains of the genus Lactobacilli (Naveena et al., 2005; Ohkouchi and Inoue, 2006). [...]

Prior exposure of Vibrio parahaemolyticus and V. vulnificus cells to pH 5.5 resulted in an adaptive acid tolerance response of these bacteria to pH 4.0. Acid adapted V. parahaemolyticus and V. vulnificus cells at pH 5.5 for 1 h were reduced by 5 logs within 2 h after exposure to pH 4.0, while non-acid adapted cells were reduced by 4.5 logs within 15 to 30 min after exposure to pH 4.0. Chloramphenicol treated cells were not acid tolerant and were reduced by more than 5 logs within 10 min after exposure to pH 4.0 conditions. This study suggests that development of acid tolerance in V. parahaemolyticus and V. vulnificus may increase the likelihood of these bacteria to survive the acid environment found in the human stomach.

Two new epiphytes of anamorphic ascomycetes, Phaeomoniella zymoides sp. nov. and Phaeomoniella pinifoliorum sp. nov., were isolated from the needle surface of Pinus densiflora in Korea. The new taxa were characterized by acid-tolerant, slow, partially yeast-like growth and extensive production of emerging cells on convex wrinkled mycelial colonies. Phaeomoniella zymoides produced mycelium with large numbers of intercalary and lateral or terminal vesicles or swollen cells. Large conidiogenous cells had a swollen base and appeared to be phialidic, and many phialoconidia also were produced from lateral hyphal apertures. Maturing colonies of Ph. zymoides were made up of dark green to blackish areas and produced a Phoma-like synanamorph. Primary conidia became elongate mother cells giving rise to polar or lateral secondary conidia. Phaeomoniella pinifoliorum was characterized by reduced, swollen, phialide-like cells, lateral production of conidia from hyphae and terminal or subterminal, or less commonly lateral, secondary production of conidia from yeast-like primary conidia. When ITS and 28S rDNA sequences were compared and analyzed with those of best matching GenBank taxa, the Phaeomoniella group consisted of three lineages, "zymoides", "pinifoliorum" and "chlamydospora" clades, which again showed a complete sister relationship to Moristroma quercinum ined.

From acidic tea soils of Kagoshima Prefecture in Japan, some soil properties were determined and 38 strains of acid tolerant microorganisms were isolated. Different Al3+ concentrations were applied to YG media to estimate Al resistance. Selected microbial strains could grow strongly in the liquid media in the presence of 100 mM Al3+ and survive even in 300 mM Al3+ at pH 3.0. Their base sequences of 28S rDNA-D1/D2 were determined and sequence data were searched using the Basic Local Alignment Search Tool (BLAST) system. The results of sequencing revealed that the isolates belong to two different species, Cryptococcus sp. and Candida palmioleophila. When cultivated with various Al3+ concentrations, the yeast growth was inhibited at a concentration of 200 mM. Pre-cultivation of these strains with 0–30 mM Al3+ did not promote the growth response caused by Al3+. Inductively-Coupled Plasma-Mass Spectrometry (ICP-MS) was used to assess the elimination of Al. The amount of Al remaining in culture media was decrea...

Clostridium drakei SL1(T) is a strictly anaerobic, H2-utilizing, and acid-tolerant acetogen isolated from an acidic sediment that is a potential platform for commodity chemical production from syngas fermentation. The draft genome sequence of this strain will enable determination of the acid resistance and autotrophic pathway of the acetogen.

Two strains of acid-tolerant and starch-degradable yeast were isolated from rivers flowing in Kusatsu and Manza, considering an effective reuse of great mass of starch-based biodegradable plastic. The isolated strains could grow in acid media of pH 1.8 and were identified as Candida fluviatinis and Candida intermedia. The yeasts could assimilate many carbon sources and ferment glucose and sucrose in acid media to alcohol.

Clostridium drakei SL1 T is a strictly anaerobic, H 2 -utilizing, and acid-tolerant acetogen isolated from an acidic sediment that is a potential platform for commodity chemical production from syngas fermentation. The draft genome sequence of this strain will enable determination of the acid resistance and autotrophic pathway of the acetogen.

Fungi have not been systematically studied from mines and mine drainage waters, even though they are often encountered there. This paper provides a key from literature sources and lists morphological characteristics and habitat information for the 81 fungal species that have been collected or identified in pH