Transcriptome analysis of Acinetobacter calcoaceticus HX09 strain with outstanding crude-oil-degrading ability.

Microbial remediation plays a pivotal role in the elimination of petroleum pollutants, making it imperative to investigate the capabilities of microorganisms in degrading petroleum. The present study describes the isolation of a promising strain, Acinetobacter sp. HX09, from petroleum-contaminated water. GC-MS analysis revealed a remarkable removal efficiency for short and medium-chain alkanes, with a rate of approximately 64% after a 7-days incubation at 30 °C. Transcriptome analysis of HX09 exhibited a predominant upregulation in gene expression levels by the induce of crude oil. Notably, genes such as alkane 1-monooxygenase, dehydrogenases and fatty acid metabolic enzymes exhibited fold changes range from 3.16 to 1.3. Based on the alkB gene sequences in HX09, the Phyre2 algorithm generated a three-dimensional structure that exhibited similarity to segments of acyl coenzyme desaturases and acyl lipid desaturases. Furthermore, three biodegradation-related gene clusters were predicted in HX09 based on the reference genome sequence. These findings contribute to our understanding of the hydrocarbon-degrading mechanisms employed by Acinetobacter species and facilitate the development of effective remediation strategies for crude oil- polluted environments.

Nocardioides: "Specialists" for Hard-to-Degrade Pollutants in the Environment.

Nocardioides, a genus belonging to Actinomycetes, can endure various low-nutrient conditions. It can degrade pollutants using multiple organic materials such as carbon and nitrogen sources. The characteristics and applications of Nocardioides are described in detail in this review, with emphasis on the degradation of several hard-to-degrade pollutants by using Nocardioides, including aromatic compounds, hydrocarbons, haloalkanes, nitrogen heterocycles, and polymeric polyesters. Nocardioides has unique advantages when it comes to hard-to-degrade pollutants. Compared to other strains, Nocardioides has a significantly higher degradation rate and requires less time to break down substances. This review can be a theoretical basis for developing Nocardioides as a microbial agent with significant commercial and application potential.

Dynamics of Bacterial Diversity and Functions with Physicochemical Properties in Different Phases of Pig Manure Composting.

Bacteria are key drivers in regulating ecosystem functions, and understanding the diversity and dynamic changes in bacteria in composting is very important for optimizing compost. This study investigated the structure, composition, and function of bacterial communities in alkaline pig manure compost using Miseq sequencing, PICRUSt2. The ACE and Chao1 indices of the bacterial communities in various phases were significantly different. Bacterial communities of alkaline pig compost were different from neutral and acidic swine manure compost, and there were 438 genera of common bacteria in various stages. The main bacterium was the phylum Firmicutes. There were six genera, including Romboutsia, Clostridium, Terrisporobacter, norank_f_Marinococcaceae, Saccharomonospora, and unclassified_f_Bacillaceae, that were significantly correlated (p < 0.05), or even extremely significantly correlated (p < 0.001), with the physicochemical properties. TOC, moisture, C/N, and Tem were the key factors that caused changes in bacterial communities in composting. PICRUSt2 analysis showed that there were seven functional groups: metabolism (45.02-48.07%), environmental information processing (15.25-16.00%), genetic information processing (16.97-20.02%), cellular processes (3.63-4.37%), human diseases (0.71-0.82%), organismal systems (0.66-0.77%), and unclassified (13.93-14.36%). This study will provide a reference for improving bacteria growth and reproduction conditions in pig manure composting, optimizing the process, and improving the efficiency of composting.

Aquatic Bacteria Rheinheimera tangshanensis New Ability for Mercury Pollution Removal.

To explore the strong tolerance of bacteria to Hg pollution, aquatic Rheinheimera tangshanensis (RTS-4) was separated from industrial sewage, with a maximum Hg(II) tolerant concentration of 120 mg/L and a maximum Hg(II) removal rate of 86.72 ± 2.11%, in 48 h under optimum culture conditions. The Hg(II) bioremediation mechanisms of RTS-4 bacteria are as follows: (1) the reduction of Hg(II) through Hg reductase encoded by the mer operon; (2) the adsorption of Hg(II) through the production of extracellular polymeric substances (EPSs); and (3) the adsorption of Hg(II) using dead bacterial biomass (DBB). At low concentrations [Hg(II) ≤ 10 mg/L], RTS-4 bacteria employed Hg(II) reduction and DBB adsorption to remove Hg(II), and the removal percentages were 54.57 ± 0.36% and 45.43 ± 0.19% of the total removal efficiency, respectively. At moderate concentrations [10 mg/L < Hg(II) ≤ 50 mg/L], all three mechanisms listed above coexisted, with the percentages being 0.26 ± 0.01%, 81.70 ± 2.31%, and 18.04 ± 0.62% of the total removal rate, respectively. At high concentrations [Hg(II) > 50 mg/L], the bacteria primary employed EPS and DBB adsorption to remove Hg(II), where the percentages were 19.09 ± 0.04% and 80.91 ± 2.41% of the total removal rate, respectively. When all three mechanisms coexisted, the reduction of Hg(II) occurred within 8 h, the adsorption of Hg(II) by EPSs and DBB occurred within 8-20 h and after 20 h, respectively. This study provides an efficient and unused bacterium for the biological treatment of Hg pollution.

Arsenic pollution remediation mechanism and preliminary application of arsenic-oxidizing bacteria isolated from industrial wastewater.

Microbial remediation is vital for improving heavy metal-polluted water. In this work, two bacterial strains, K1 (Acinetobacter gandensis) and K7 (Delftiatsuruhatensis), with high tolerance to and strong oxidation of arsenite [As(III)], were screened from industrial wastewater samples. These strains tolerated 6800 mg/L As(III) in a solid medium and 3000 mg/L (K1) and 2000 mg/L (K7) As(III) in a liquid medium; arsenic (As) pollution was repaired through oxidation and adsorption. The As(III) oxidation rates of K1 and K7 were the highest at 24 h (85.00 ± 0.86%) and 12 h (92.40 ± 0.78%), respectively, and the maximum gene expression levels of As oxidase in these strains were observed at 24 and 12 h. The As(III) adsorption efficiencies of K1 and K7 were 30.70 ± 0.93% and 43.40 ± 1.10% at 24 h, respectively. The strains exchanged and formed a complex with As(III) through the -OH, -CH3, and C]O groups, amide bonds, and carboxyl groups on the cell surfaces. When the two strains were co-immobilized with Chlorella, the adsorption efficiency of As(III) improved (76.46 ± 0.96%) within 180 min, thereby exhibiting good adsorption and removal effects of other heavy metals and pollutants. These results outlined an efficient and environmentally friendly method for the cleaner production of industrial wastewater.

Succession of the Bacterial Communities and Functional Characteristics in Sheep Manure Composting.

Bacterial community is a key factor affecting aerobic composting, and understanding bacterial community succession is important to revealing the mechanism of organic matter degradation. In this study, the succession and metabolic characteristics of bacterial communities were explored in 45 days composting of sheep manure and wheat straw by using high-throughput sequencing technology and bioinformatics tools, respectively. Results showed that the alpha diversity of bacterial community significantly decreased in the thermophilic (T2) phase and then recovered gradually in the bio-oxidative (T3) and the maturation (T4) phases. Bacterial communities varied at different stages, but there were 158 genera in common bacterial species. Unclassified_f_Bacillaceae, Oceanobacillus, Bacillus, Pseudogracilibacillus, and Nocardiopsis were identified as keystone bacterial genera. Eleven genera were significantly correlated (p < 0.05), or even extremely significantly correlated (p < 0.001), with the physicochemical factors. Redundancy analysis (RDA) showed that changes of bacterial community diversity correlated with physicochemical factors. The highest relative abundances were amino acid and carbohydrate metabolism among the metabolic groups in the compost. These results will provide theoretical support for further optimizing sheep manure composting conditions and improving the quality of organic fertilizers.

Transcriptome analysis reveals manganese tolerance mechanisms in a novel native bacterium of Bacillus altitudinis strain HM-12.

Bacillus altitudinis HM-12, isolated from ferromanganese ore tailings, can resist up to 1200 mM Mn(II) when exposed to concentrations from 50 mM to 1400 mM. HM-12 exhibited high Mn(II) removal efficiency (90.6 %). We report the transcriptional profile of HM-12 using RNA-Seq and found 423 upregulated and 536 downregulated differentially expressed genes (DEGs) compared to the control. Gene Ontology analysis showed that DEGs were mainly linked with transporter activity, binding, catalytic activity in molecular function, cellular anatomical entity in cellular component, cellular process, and metabolic process. Kyoto Encyclopedia of Genes and Genomes analysis showed that DEGs were mostly mapped to membrane transport, signal transduction, carbohydrate and amino acid metabolism, energy metabolism, and cellular community pathways. Transport analysis showed that two manganese importer systems, mntH and mntABC, were significantly downregulated. The manganese efflux genes (mneS, yceF and ykoY) exhibited significant upregulation. Manganese homeostasis seems to be subtly regulated by manganese uptake and efflux genes. Moreover, it was found that copA as a Mn(II) oxidase gene and a copper chaperone gene copZ were considerably upregulated by signal transduction analysis. csoR encoding a transcriptional repressor which can regulate the copZA operon was upregulated. The strong Mn(II) oxidizing activity of HM-12 was also confirmed by physicochemical characterization. In metabolism and environmental information processing, yjqC encoding manganese catalase was significantly upregulated, while katE and katX encoding heme catalases were significantly downregulated. The antioxidant gene pcaC was significantly upregulated, but ykuU encoding alkyl hydroperoxide reductase, yojM encoding superoxide dismutase, and perR encoding redox-sensing transcriptional repressor were downregulated. These results highlight the oxidative activity of HM-12 by regulating the transcription of oxidase, catalase, peroxidase, and superoxide dismutase to sense the cellular redox status and prevent Mn(II) intoxication. This study provides relevant information on the biological tolerance and oxidation mechanisms in response to Mn(II) stress.

Screening of Siderophore-Producing Bacteria and Their Effects on Promoting the Growth of Plants.

Iron deficiency is a major global agricultural problem. Siderophores can help organisms to uptake iron in form of siderophore-Fe3+ complexes and then in the cell cytosol, iron is reducted and released in ferrous form. This research aimed to obtain some efficient siderophore-producing bacterial strains and evaluate their plant growth-promoting effects in the iron-deficit environment. Two strains, Brucella sp. E7 and Pseudomonas brassicae W7, were isolated from rhizosphere soil. Both strains could produce maximum siderophores under the optimal conditions. Plant promoting experiment showed that many indicators of Vigna radiata seedling were all increased significantly by strain E7/W7 or the consortium of E7 + W7. Under no-iron and high iron stress, the inoculation treatment also showed growth promotion effects on both Vigna radiata and Lolium multiflorum. These results indicated that the potential ability of strain E7 and W7 in increasing agricultural production as a growth-promoting agent in iron-deficit soil.

Profiling multiple heavy metal contamination and bacterial communities surrounding an iron tailing pond in Northwest China.

Northwest China is abundant in iron ore reserves and has become one of the important iron ore mining bases in China. However, the contamination and microbial community structure of iron tailing ponds in Northwest China have not been extensively investigated. In the present study, we characterized the main physicochemical properties, the multiple heavy metal contamination, and the bacterial community structure of the soils surrounding an iron tailing pond in Linze County, Zhangye city, Gansu Province. The tailing-associated soils were barren, exhibiting alkaline pH and low organic matter (OM), total nitrogen (TN) and total potassium (TK) compared with the control areas. There was considerable multiple heavy metal pollution in the iron tailing pond, mainly including lead (Pb), manganese (Mn), arsenic (As), cadmium (Cd), zinc (Zn), iron (Fe) and copper (Cu). Among the 303 identified core operational taxonomic units (OTUs), Actinobacteria, Proteobacteria and Deinococcus-Thermus were predominant at the phylum level, and Blastococcus, Arthrobacter, Marmoricola, Kocuria, Truepera, and Sphingomonadaceae were prevalent at a finer taxonomic level. The bacterial richness and diversity of the tailing samples were significantly lower than those of the reference samples. RDA, VPA and Spearman correlation analyses showed that the soil pH, CEC, OM, TP, TK, Cd, Pb, Ni, Zn, As and Mn had significant effects on the bacterial community composition and distribution. This work profiles the basic features of the soil physicochemical properties, the multiple heavy metal contamination and the bacterial community structure in an iron tailing pond in Northwest China, thereby providing a foundation for the future ecological remediation of the iron tailing environment in the area.

Pollution status of the Yellow River tributaries in middle and lower reaches.

To determine the water quality status of the primary tributaries in middle and lower reaches of the Yellow River Basin, water collected from the confluence of the ten tributaries and some physical, chemical and biological parameters were analyzed, and then water quality index and health risk were evaluated. Of the ten main tributaries in the middle and lower reaches, only the Qingshui River had water of medium quality in the upper reaches, while all the other tributaries contributed water of poor quality. The Jindi and Dawen rivers in the lower reaches had the poorest water quality, especially the Jindi River. TP, TN, BOD5, COD, TOC and coliform bacteria exceeded the national criteria by 155%, 1%, 97.5%, 35.5%, 114.2%, and 80%, respectively. Cluster analysis indicated that industrial, agricultural, and domestic sewage, along with industrial waste gas, were the main sources of pollution in these tributaries. An analysis of the bacterial community structure showed that the Jindi River was the most polluted and had the largest species diversity and richness of bacteria. Also, its number of pathogenic microorganisms was much higher than that of other areas, and the bacterial functional genes of related metabolic pathways were significantly enriched. This was in sharp contrast with that of the Qingshui River, which had the best water quality. We suggest more specifics policy should be taken for different tributaries, and poor water quality of Jindi and Dawen River should be further studied to explore the most suitable pollution control methods.

Three kinds of ammonia oxidizing microorganisms play an important role in ammonia nitrogen self-purification in the Yellow River.

To develop the microbial resources of the Yellow River, seven water samples were collected along the Lanzhou region of the river from upstream to downstream for testing. Analysis of various physico-chemical indexes was conducted, and key parameters influencing the water quality were selected through principal component analysis, after which the decisive factors impacting water quality were determined by correlation and regression analysis. The results indicated that (1) DO, NH3-N, NO2--N, TN, TC, As, Cr6+ and Pb were the main physico-chemical factors influencing water quality in the Lanzhou region, with NH3-N having the greatest effect. (2) Ammonia-oxidizing microorganisms [ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and anaerobic ammonia-oxidizing bacteria (AMX)] were found to mediate the transformation of NH3-N in the studied section. AOA was the primary microbe community among the two aerobic ammonia-oxidizing microorganisms (AOA and AOB) in the Yellow River. (3) Phylogenetic analysis showed that there were some known groups, and there were still many unknown species in the water of the studied section, especially within the AMX population. (4) Correlation analysis revealed that AOA has strong adaptability to unhealthy environments, and that some environmental factors (higher concentrations of carbon, nitrogen and some heavy metals) could increase the AOA gene abundance. Overall, these results suggested there are rich ammonia-oxidizing microbial resources, especially AOA, in the Lanzhou section of the Yellow River, which have the potential for application in nitrogen sewage treatment.

Analysis of growth and lipid production characteristics of Chlorella vulgaris in artificially constructed consortia with symbiotic bacteria.

The aim was to study the effect of artificially constructed consortia of microalgae-bacterial symbionts on growth and lipid production by Chlorella vulgaris (C. vulgaris), as well as the inter-relationship between microalgae and bacterial in a photoautotrophic system. The results showed that compared to an axenic culture of C. vulgaris, H1 co-culture system (axenic C. vulgaris-Stenotrophomona smaltophilia) had the strongest effect on the C. vulgaris growth. The biomass, specific growth rate and maximum productivity of C. vulgaris were increased by 21.9, 20.4, and 18%, respectively. The bacteria in co-culture system had a significant effect on the accumulation of lipid and fatty acid components of C. vulgaris: the content of lipid was increased by 8.2-33.83%, and the components of the saturated fatty acids and oleic acids also had an obvious improvement. The results indicate that the microalgae-bacterial co-culture system can improve microalgal biomass and the quality of biodiesel.

Greater health risk in wet season than in dry season in the Yellow River of the Lanzhou region.

The Yellow River flows through Lanzhou city and is the only drinking water source for 3.6 million residents. Yet, little is known regarding the safety and quality of the Yellow River for resident consumption. To address this knowledge-gap, water samples were collected from different sites within this section during the dry and wet seasons. Physico-chemical parameters and microbial community metrics were analyzed to assess the health risk associated with this Chinese mother river. Water quality of the river was better during the dry season (March-April) than in the wet season (September-October). Fifteen conventional physico-chemical and biological indices, such as NH3-N, NO2--N, total nitrate (TN), five day biochemical oxygen demand (BOD5), chemical oxygen demand (COD), volatile phenol (VP), and coliform abundances, generally exceeded acceptable standards. The average abundance of coliforms was 2.8 times that of acceptable standards in the dry season and 4.6 times the standards in the wet season. The concentration of the toxic metal As was more than two times than that of the national standard in waters from the wet season. Microbial community analysis also indicated that community diversity and species richness were positively correlated with the concentrations of several physico-chemical parameters. The results indicate that As and Cr6+ pose potential risk for human health through consumption by residents. Further, the results indicated that human activities are the main causes of water pollution, and that long-term strict monitoring should be conducted to ensure the safety of drinking water consumption and the health of the environment.

[Recent advances in lanthipeptide biosynthesis - A review].

Lanthipeptides are a growing class of ribosomally synthesized and posttranslationally modified peptide (RiPP) natural products. These compounds are widely distributed among taxonomically distant species, and their structures and biological activities are diverse, providing an important source for drug research and developement. In this review, we summarized the recent advances in the understanding of structure, classification, evolution and substrate-controlled biosynthetic mechanism of lanthipeptide, attempting to highlight the intriguing chemistry and enzymology in the biosynthesis of this growing family of natural products.

Counteractive action of nitric oxide on the decrease of nitrogenase activity induced by enhanced ultraviolet-B radiation in cyanobacterium.

The experimental enhancement of UV-B radiation resulted in damage to chlorophyll-a in Spirulina platensis 794, and the degree of this damage was modified by chemical treatments. The addition of 0.5 mM sodium nitroprusside (SNP), a donor of nitric oxide (NO), to cultures of Spirulina platensis 794 could markedly alleviate the damage to chlorophyll-a caused by enhanced ultraviolet-B radiation. Exposure of N(2)-fixing cyanobacterium Spirulina platensis 794 to enhanced ultraviolet-B radiation resulted in an intensity-dependent inhibition of nitrogenase activity. In cultured cells that were treated with 0.5 mM SNP and enhanced UV-B for 6 h, nitrogenase activity increased by 47.3% compared with UV-B treated control cells. SNP apparently counteracted the decrease in nitrogenase activity caused by UV-B stress. NAC (a free radical scavenger) significantly increased nitrogenase activity, but PTIO (a nitric oxide scavenger) decreased nitrogenase activity in UV-B treated S. platensis 794. Thus, the free radical scavenger NAC and NO may counteract the effects of enhanced UV-B radiation. The activity of UV-B-inhibited nitrogenase did not recover upon transfer of exposed cells to fluorescent light, suggesting that the inhibition may be due to specific inactivation of the enzyme. By experimentally manipulating the inhibitors of photosystem-II activity, it was demonstrated that nitrogenase activity in cyanobacterium S. platensis 794 is limited by the amount of reductant and ATP. This result further confirmed that nitrogenase activity requires a continued and abundant supply of suitable reductant and ATP for conversion of N(2) to NH(3). The effects of UV-B treatment on nitratase activity were also examined, and enhanced UV-B radiation increased nitratase activity. In addition, enhanced UV-B in combination with SNP and NAC resulted in significant increases in the activity of nitratase.

Nitric oxide alleviates oxidative damage induced by enhanced ultraviolet-B radiation in cyanobacterium.

To study the role of nitric oxide (NO) on enhanced ultraviolet-B (UV-B) radiation (280-320 nm)-induced damage of Cyanobacterium, the growth, pigment content, and antioxidative activity of Spirulina platensis-794 cells were investigated under enhanced UV-B radiation and under different chemical treatments with or without UV-B radiation for 6 h. The changes in chlorophyll-a, malondialdehyde content, and biomass confirmed that 0.5 mM: sodium nitroprusside (SNP), a donor of nitric oxide (NO), could markedly alleviate the damage caused by enhanced UV-B. Specifically, the biomass and the chlorophyll-a content in S. platensis-794 cells decreased 40% and 42%, respectively under enhanced UV-B stress alone, but they only decreased 10% and 18% in the cells treated with UV-B irradiation and 0.5 mM: SNP. Further experiments suggested that NO treatment significantly increased the activities of superoxide dismutase (SOD) and catalase (CAT), and decreased the accumulation of O (2)(-) in enhanced UV-B-irradiated cells. SOD and CAT activity increased 0.95- and 6.73-fold, respectively. The accumulation of reduced glutathione (GSH) increased during treatment with 0.5 mM: SNP in normal S. platensis cells, but SNP treatment could inhibit the increase of GSH in enhanced UV-B-stressed S. platensis cells. Thus, these results suggest that NO can strongly alleviate oxidative damage caused by UV-B stress by increasing the activities of SOD, peroxidase, CAT, and the accumulation of GSH, and by eliminating O (2)(-) in S. platensis-794 cells. In addition, the difference of NO origin between plants and cyanobacteria are discussed.

[Alleviative effects of nitric oxide on the biological damage of spirulina platensis induced by enhanced ultraviolet-B].

Continuing depletion of the stratospheric ozone layer by atmospheric pollutants, in particular chlorofluorocarbons (CFCs), has resulted in an increasing incidence of solar UV-B (280-320 nm) at the Earth's surface. Enhanced UV-B radiation has been considered as important global environmental problem and results in important effects to mankind and the entire global ecosystem. Nitric oxide (NO) is not only a toxic molecule, one of reactive nitrogen species (RNS), but also an important redox-active signaling molecule. NO is really a double-edged sword, it can be either beneficial and activate defense responses in plants and animals or toxic, together with ROS. Besides those, NO can also act as a signal molecule and play very important roles in life of organisms. To study the effects of NO on the biological specific property of enhanced UV-B stressed Spirulina platensis, the chlorophyll-a, protein contents and biomass were investigated under enhanced UV-B radiation and its combination with different chemical treatment. The changes of chlorophyll-a, protein contents and biomass confirmed that 0.5 mmol/L sodium nitroprusside (SNP), a donor of nitric oxide (NO), could markedly alleviate the biological damage of cyanobacteria-Spirulina platensis 794 caused by enhanced ultraviolet-B. Further results proved that NO significantly increase the content of protein and proline. Meanwhile, the accumulation of reduced glutathione (GSH) in S. platensis cells were raised under normal growth condition. But exogenous NO could decrease the increasing of reduced glutathione (GSH) in enhanced UV-B stressed S. platensis cells. These results suggest that NO has protective effect and can strongly alleviate biological damage caused by UV-B stress in S. platensis 794 cells. For the first time, reported the effect of NO on the regulating ability of biological damage of S. platensis induced by enhanced UV-B. Therefore, further investigations will be necessary to inquire into the interaction and inter-correlation of signal molecules and the mechanism in cyanobacterium under enhanced UV-B stress.

Molecular cloning and characterization of a novel MAP kinase gene in Chorispora bungeana.

Chorispora bungeana Fisch. and C.A. Mey (Chorispora bungeana) is a rare alpine subnival plant species that is highly capable of resisting freezing environment. Since it is a stress-tolerant plant, we investigated the participation of mitogen-activated protein kinases (MAPKs) as possible mediators of abiotic stresses. We have isolated from Chorispora bungeana a new MAPK cDNA CbMAPK3 which encodes a 369 amino-acid protein with moderate to high nucleotide sequence similarity to previously reported plant MAPK genes. CbMAPK3 contains all 11 of the MAPK conserved subdomains and the phosphorylation motif TEY. The transcripts of CbMAPK3 were detected and no tissue-specific expression were observed in both roots and leaves, The transcripts of CbMAPK3 accumulated highly and rapidly when Chorispora bungeana treated with cold (4 and -4 degrees C), ABA and salinity stress. These results indicate that the CbMAPK3 may play an important role in response to environmental stresses.

Effects of enhanced ultraviolet-B radiation on algae and cyanobacteria.

This article provides an overview of existing literature on the ultraviolet-B (UV-B) radiation effects on algae and cyanobacteria. We report on the effects of UV-B radiation to the growth and development, biomass, sensitivity, photosynthetic pigments, UV-B absorbing compounds, photosynthesis, protein and DNA damage, enzyme activity, nitrogen fixation and assimilation of nitrogen, protective mechanisms of algae and cyanobacteria, the accommodation of algae and cyanobacteria to environmental stress, and the effects to ecology system. Many of the studies show the dramatic effects of UV-B radiation; but typically these studies were conducted under conditions with supplemental UV-B irradiance that was higher than would ever occur outside experimental conditions or natural condition. A few of the studies reviewed used experimental conditions and supplemental UV-B irradiance that approached realism. Enhanced UV-B generally decreased chlorophyll content, whereas it increased UV-B absorbing compounds in many algae. Decrease in photosynthesis, particularly at higher UV-B doses, was due to both direct (effect on photosystem) and indirect (decrease in pigments) effects. The decreases in chlorophyll pigments and photosynthesis resulted in lower biomass. However, algae and cyanobacteria have evolved various avoidance and repair mechanisms to protect themselves against the damaging effects of UV radiation to acclimate to enhanced UV-B radiation. The review points to areas where further studies on the relationships among nitrogenase, Rubisco, antioxidase activity, signal, antioxidants, and free radicals under enhanced UV-B are needed to quantify the effects of UV-B radiation on algae and cyanobacteria. These studies are needed in order to develop dose response functions that can facilitate development of dynamic simulation models for use in UV-B and other environmental impact assessments.