Halotolerant Bacterial Strains Research Articles

Optimization of poly-β-hydroxybutyrate production by halotolerant bacterial strains isolated from saline environment

PHB is a biodegradable plastic which is becoming an environmentally friendly substitute to the synthetic plastics that are persistent and accumulate in large amounts and are non-degradable. PHB is a class of Polyhydroxyalkanoate which are similar to commercial plastics like polypropylene but with an added advantage of being biodegradable. To overcome the problem of commercializing PHB production by microorganisms because of the high cost involved, Halotolerant organisms can be used as they are easier to cultivate and do not require strict sterile conditions. In this present study PHB producing halotolerant bacterial strains were isolated from a marine environment and cultivated under saline conditions. The growth conditions of the bacterial strains were optimized for maximum production of PHB. The parameters such as pH, temperature, NaCl concentration, carbon sources, nitrogen sources and carbon and nitrogen ratio were optimized and studied. The growth conditions for each of the parameter were optimized and the PHB production was estimated for the bacterial strains under saline conditions. The optimum pH and temperature range yielded maximum PHB production of about 42 – 45 mg/100ml and 30 – 40 mg/100ml respectively. The perspective application of PHB could be in the medicinal field for manufacturing medical devices as implants for various surgeries such as dental, cranio – maxillofacial and dental surgeries.

Chemical Oxygen Demand Removal in Na2SO4 Saturated Wastewater by Cultivable Halotolerant Bacterial Community

Industrial wastewater with a high Na2SO4 concentration is characterized by high osmotic pressure and salinity, and requires pretreatment before discharging into central treatment facilities. To date, few studies have addressed the chemical oxygen demand (COD) removal in biotreatment of Na2SO4 wastewater. Here, a novel aerobic system for treating Na2SO4 wastewater was developed based on screening halotolerant bacterial strains. The system maintained a stable COD removal at >90% in saturated concentration (varying from 5 to 40% depending on the temperature) of Na2SO4 for 5 years. Activated sludge was initially constructed by cultured strains of Hyphomicrobium sp. CB03, Dietzia sp. XM15, Staphylococcus sp. T211, Flavobacterium sp. AXY1, Ochrobactrum sp. BY4, Bacillus sp. BYXT, Sphingobacterium sp.YY1, Rhodococcus sp. NH7‐4, Stappia sp. HM4, Microbacterium sp. PY3‐1, and Pseudomonas sp. MN3‐2. Uncultured phylum TM7 was detected in the sludge after acclimatization. The present aerobic cultivable halotolerant bacterial community was successfully applied to large scale removal of organic pollutants in saline wastewater.

Alleviation of salt stress by halotolerant and halophilic plant growth-promoting bacteria in wheat ( Triticum aestivum )

In the current study, 18 halotolerant and halophilic bacteria have been investigated for their plant growth promoting abilities in vitro and in a hydroponic culture. The bacterial strains have been investigated for ammonia, indole-3-acetic acid and 1-aminocyclopropane-1-carboxylate-deaminase production, phosphate solubilisation and nitrogen fixation activities. Of the tested bacteria, eight were inoculated with Triticum aestivum in a hydroponic culture. The investigated bacterial strains were found to have different plant-growth promoting activities in vitro. Under salt stress (200 mM NaCl), the investigated bacterial strains significantly increased the root and shoot length and total fresh weight of the plants. The growth rates of the plants inoculated with bacterial strains ranged from 62.2% to 78.1%.Identifying of novel halophilic and halotolerant bacteria that promote plant growth can be used as alternatives for salt sensitive plants. Extensive research has been conducted on several halophilic and halotolerant bacterial strains to investigate their plant growth promoting activities. However, to the best of my knowledge, this is the first study to inoculate these bacterial strains with wheat.

The potential of halophilic and halotolerant bacteria for the production of antineoplastic enzymes: L-asparaginase and L-glutaminase.

L-asparaginase and L-glutaminase can be effectively used for the treatment of patients who suffer from accute lymphoblastic leukemia and tumor cells. Microbial sources are the best source for the bulk production of these enzymes. However, their long-term administration may cause immunological responses, so screening for new enzymes with novel properties is required. Halophilic and halotolerant bacteria with novel enzymatic characteristics can be considered as a potential source for production of enzymes with different immunological properties. In this study, L-asparaginase and L-glutaminase production by halophilic bacteria isolated from Urmia salt lake was studied. Out of the 85 isolated halophilic and halotolerant bacterial strains, 16 (19 %) showed L-asparaginase activity and 3 strains (3.5 %) showed L-glutaminase activity. Strains with the highest activities were selected for further studies. Based on 16S rDNA sequence analysis, it was shown that the selected isolates for L-asparaginase and L-glutaminase production belong to the genus Bacillus and Salicola, respectively. Both enzymes were produced extracellularly. The strain with the most L-asparaginase production did not show L-glutaminase production which is medically important. The effects of key parameters including temperature, initial pH of the solution, and concentrations of glucose, asparagine or glutamine, and sodium chloride were evaluated by means of response surface methodology (RSM) to optimize enzymes production. Under the obtained optimal conditions, L-asparaginase and L-glutaminase production was increased up to 1.5 (61.7 unit/mL) and 2.6 fold (46.4 unit/mL), respectively.

Taxonomic description and genome sequence of Salinicoccus sediminis sp. nov., a halotolerant bacterium isolated from marine sediment.

A Gram-staining-positive, coccoid, halotolerant bacterial strain, designated SV-16T, was isolated from marine sediment and subjected to a polyphasic taxonomic study. The strain exhibited phenotypic properties that included chemotaxonomic characteristics consistent with its classification in the genus Salinicoccus. Growth occurred at temperatures in the range 25-37 °C (optimum 30 °C), at pH 7.0-11.0 (optimum pH 8.0) and at NaCl concentrations of up to 25.0% (optimum 15.0%). The highest level of 16S rRNA gene sequence similarity was with Salinicoccus carnicancri CrmT (98.6%) followed by Salinicoccus halodurans W24T (96.6%). The predominant polar lipids were diphosphatidylglycerol, phosphatidylinositol and phosphatidylglycerol. The major cellular fatty acids were iso-C15:0, anteiso-C15:0, iso-C17:0 and anteiso-C17:0. The draft genome of strain SV-16T consisted of 2,591,284 bp with a DNA G+C content of 48.7 mol%. On the basis of the phenotypic characteristics and genotypic distinctiveness of strain SV-16T, it should be classified within a novel species of the genus Salinicoccus, for which the name Salinicoccus sediminis sp. nov. is proposed. The type strain is SV-16T ( = MTCC 11832T = DSM 28797T).

Isolation and Characterization of Salt-Tolerant Bacterial Strains in Salt-Affected Soils of Erzurum, Turkey

In the current study, 18 salt-tolerant bacteria were isolated from salt-affected soil of Erzurum, Turkey. Forty-five bacterial isolates were identified and characterized by conventional and molecular techniques. These 45 sequenced isolates were identified as 16 different genus including Bacillus (19 isolates), Staphylococcus (3 isolates), Halobacillus (4 isolates), Zhihengliuella (2 isolates), Oceanobacillus (2 isolates), Halomonas (1 isolate), Nesterenkonia (2 isolates), Promicromonospora (2 isolates), Jeotgalibacillus (2 isolates), Planococcus (2 isolates), Virgibacillus (1 isolate), Terribacillus (1 isolate), Thalassobacillus (1 isolate), Marinibacillus (1 isolate), Gracilibacillus (1 isolate) and Microbacterium (1 isolate). According to the results obtained, investigated bacterial strains have high salt tolerance and significant enzyme activities that can improve soil nutrient cycling and soil fertility. The current article provides the evaluation and diversity of the potential halotolerant and halophilic bacterial strains in salt-affected soils of Erzurum, Turkey.

Aromatic Hydrocarbon Utilization Ability of Chromohalobacter sp.

The aim of this study is to reveal the ability of utilizing different aromatic hydrocarbons (p-hydroxybenzoic acid, naphthalene, phenanthrene, and pyrene) by a halotolerant bacterial strain, Chromohalobacter sp., under saline conditions. The aromatic hydrocarbon degradation pathways were identified. PCR amplification was carried to define the gene zones which codify the dioxygenases of the isolates. The possible gene zones of catechol 1, 2 dioxygenase and protocatechuate 3, and 4 dioxygenase were determined. According to the PCR amplification and enzyme test results Chromohalobacter sp. utilizes aromatic hydrocarbons by the ortho cleavage of the s-ketoadipate pathway. In this study, it was concluded that this isolate can be used in bioremediation studies of saline environments contaminated with aromatic hydrocarbons.

Alleviation of salt stress in germination of Vigna radiata L. by two halotolerant Bacilli sp. isolated from saline habitats of Gujarat

Fifty halotolerant bacterial strains were isolated from the alkaline saline soil from the Ajod village of Vadodara district of Gujarat. All strains grew well in media supplemented with 5 % NaCl, but two strains (BR5 and BN7) could grow even at 18 % NaCl concentration. These two strains were characterized for their plant growth promoting characteristics. Both the strains were able to solubilize significant amount of phosphate and produce IAA. Both the strains also showed nitrogen fixing, siderophore production and antifungal properties against root rot pathogen of Vigna. radiata L., Fusarium sp. Potential of these halotolerant bacteria to ameliorate salt stress in V. radiata L. plants grown in saline soil inoculated with these bacteria was assessed. Both halotolerant bacteria were found to increase germination percentage, root length and shoot length compared to un inoculated control plants. Both these cultures were subjected to 16S rRNA gene sequencing and BLAST analysis, among which, BR5 showed 99 % similarity with Bacillus subtilis and BN7 showed 99 % similarity with B. megaterium.

Mitigation of salt stress in wheat seedlings by halotolerant bacteria isolated from saline habitats

Eighty four halotolerant bacterial strains were isolated from the saline habitats and screened for growth at different NaCl concentrations. All grew well at 5% NaCl, but only 25% isolates showed growth at 20% NaCl concentration. Five strains SL3, SL32, SL35, J8W and PU62 growing well in 20% NaCl concentrations were further characterized for multiple plant growth promoting traits such as indole −3- acetic acid (IAA) production, HCN and siderophore production, ACC deaminase activity and P-solubilization. None were positive for HCN production and PCR amplification of acdS, the structural gene for ACC deaminase enzyme was found negative. 16S rRNA gene sequencing analysis of the five strains showed them to belong to two genera Bacillus and Hallobacillus. In vitro experiments showed that salt concentrations had significant inhibitory effects on development of seedlings but not on the growth of the bacterial strains. Inoculation of the 5 halotolerant bacterial strains to ameliorate salt stress (80 mM, 160 mM and 320 mM) in wheat seedlings produced an increase in root length of 71.7% in comparison with uninoculated positive controls. In particular, Hallobacillus sp. SL3 and Bacillus halodenitrificans PU62 showed more than 90% increase in root elongation and 17.4% increase in dry weight when compared to uninoculated wheat seedlings at 320 mM NaCl stress indicating a significant reduction of the deleterious effects of NaCl. These results indicate that halotolerant bacteria isolated from saline environments have potential to enhance plant growth under saline stress through direct or indirect mechanisms and would be most appropriate as bioinoculants under such conditions.

Polyester production by halophilic and halotolerant bacterial strains obtained from mangrove soil samples located in Northern Vietnam.

This research article reports halophilic and halotolerant bacteria isolated from mangrove forests located in Northern Vietnam. Several of these bacteria were able to synthesize polyhydroxyalkanoates (PHAs). PHAs are polyesters stored by microorganisms under the presence of considerable amounts of a carbon source and deficiency of other essential nutrient such as nitrogen or phosphorous. Mangrove forests in Northern Vietnam are saline coastal habitats that have not been microbiologically studied. Mangrove ecosystems are, in general, rich in organic matter, but deficient in nutrients such as nitrogen and phosphorus. We have found about 100 microorganisms that have adapted to mangrove forests by accumulating PHAs. The production of polyesters might therefore be an integral part of the carbon cycle in mangrove forests. Three of the strains (ND153, ND97, and QN194) isolated from the Vietnamese forests were identified as Bacillus species, while other five strains (QN187, ND199, ND218, ND240, and QN271) were phylogenetically close related to the α-proteobacterium Yangia pacifica. These strains were found to accumulate PHAs in noticeable amounts. Polymer inclusions and chemical structure were studied by transmission electron microscopy and proton nuclear magnetic resonance (NMR) spectroscopy analyses, respectively. Strains ND153, ND97, QN194, QN187, ND240, and QN271 synthesized poly(3-hydroxybutyrate) (PHB) from glucose, whereas strains ND199 and ND218 synthesized poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) from this carbohydrate. With the exception of strain QN194, the strains accumulated PHBV when a combination of glucose and propionate was included in the culture medium. The polymer yields and cell growth reached by one Bacillus isolate, strain ND153, and one Gram-negative bacterium, strain QN271, were high and worth to be researched further. For experiments performed in shake flasks, strain ND153 reached a maximum PHBV yield of 71 wt% and a cell dry weight (CDW) of 3.6 g/L while strain QN271 attained a maximum PHB yield of 48 wt% and a CDW of 5.1 g/L. Both strain ND153 and strain QN271 may only represent a case in point that exemplifies of the potential that mangrove forests possess for the discovery of novel halophilic and halotolerant microorganisms able to synthesize different types of biopolyesters.

Degradation of Asphaltenic Fraction by Locally Isolated Halotolerant Bacterial Strains

Three halotolerant bacterial species were isolated from locally oil-polluted water sample for their ability to utilize asphaltene (Asph) fraction as sole carbon and energy source. These bacteria degrade 83–96% of 2500 mg/L asphaltene within 21 d at 30°C and pH7. They were identified as Bacillus sp. Asph1, Pseudomonas aeruginosa Asph2, and Micrococcus sp. Asph3. A statistically significant difference at 95% confidence level for cell growth and percentage biodegradation (%BD) was observed in all biotreatment flasks relative to noninoculated (–ve control) flasks. Regression analysis estimated a quadratic polynomial equation for Asph biodegradation as a function of cell growth. Gel permeation chromatographic (GPC) and Fourier transform infrared (FT-IR) analysis revealed decrease in Asph average molecular weights and significant alternations in functional groups after biotreatment, respectively.

Role of nutrients in the utilization of polycyclic aromatic hydrocarbons by halotolerant bacterial strain

A halotolerant bacterial strain VA1 isolated from marine environment was studied for its ability to utilize polycylic aromatic hydrocarbons (PAHs) under saline condition. Anthracene and pyrene were used as representatives for the utilization of PAH by the bacterial strain. Glucose and sodium citrate were used as additional carbon sources to enhance the PAH utilization. The strain VA1 was able to utilize anthracene (73%) and pyrene (66%) without any additional substrate. In the presence of additional carbon sources (glucose/sodium citrate) the utilization of PAH was faster. PAH was utilized faster by VA1 in the presence of glucose than sodium citrate. The stain utilized 87% and 83% of anthracene and pyrene with glucose as carbon source and with sodium citrate the strain utilized 81% and 76% respectively in 4 days. Urea as an alternative source of nitrogen also enhanced the utilization of PAHs (anthracene and pyrene) by the bacterial strain up to 88% and 84% in 4 days. Sodium nitrate as nitrogen source was not able to enhance the PAH utilization rate. Phenotypic and phlyogenetic analysis proved that the PAHs utilizing halotolerant strain VA1 belongs to Ochrobactrum sp.

Isolation, Characterization, and Use for Plant Growth Promotion Under Salt Stress, of ACC Deaminase-Producing Halotolerant Bacteria Derived from Coastal Soil

In total, 140 halotolerant bacterial strains were isolated from both the soil of barren fields and the rhizosphere of six naturally growing halophytic plants in the vicinity of the Yellow Sea, near the city of Incheon in the Republic of Korea. All of these strains were characterized for multiple plant growth promoting traits, such as the production of indole acetic acid (IAA), nitrogen fixation, phosphorus (P) and zinc (Zn) solubilization, thiosulfate (S2O3) oxidation, the production of ammonia (NH3), and the production of extracellular hydrolytic enzymes such as protease, chitinase, pectinase, cellulase, and lipase under in vitro conditions. From the original 140 strains tested, on the basis of the latter tests for plant growth promotional activity, 36 were selected for further examination. These 36 halotolerant bacterial strains were then tested for 1- aminocyclopropane-1-carboxylic acid (ACC) deaminase activity. Twenty-five of these were found to be positive, and to be exhibiting significantly varying levels of activity. 16S rRNA gene sequencing analyses of the 36 halotolerant strains showed that they belong to 10 different bacterial genera: Bacillus, Brevibacterium, Planococcus, Zhihengliuella, Halomonas, Exiguobacterium, Oceanimonas, Corynebacterium, Arthrobacter, and Micrococcus. Inoculation of the 14 halotolerant bacterial strains to ameliorate salt stress (150 mM NaCl) in canola plants produced an increase in root length of between 5.2% and 47.8%, and dry weight of between 16.2% and 43%, in comparison with the uninoculated positive controls. In particular, three of the bacteria, Brevibacterium epidermidis RS15, Micrococcus yunnanensis RS222, and Bacillus aryabhattai RS341, all showed more than 40% increase in root elongation and dry weight when compared with uninoculated saltstressed canola seedlings. These results indicate that certain halotolerant bacteria, isolated from coastal soils, have a real potential to enhance plant growth under saline stress, through the reduction of ethylene production via ACC deaminase activity.

Biodegradation of polycyclic aromatic hydrocarbons by a halotolerant bacterial strain Ochrobactrum sp. VA1

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous pollutants in the environment and are derived from both man-made and natural resources. The present study is focused on the degradation of PAHs by a halotolerant bacterial strain under saline conditions. The bacterial strain VA1 was isolated from a PAH-degrading consortium that was enriched from marine water samples that were collected from different sites at Chennai, India. In the present study, a clearing zone formed on PAH-amended mineral salt agar media confirmed the utilization of PAH by the bacterial strain VA1. The results show that the strain VA1 was able to degrade anthracene (88%), phenanthrene (98%), naphthalene (90%), fluorene (97%), pyrene (84%), benzo(k)fluoranthene (57%) and benzo(e)pyrene (50%) at a 30g/L NaCl concentration. The present study reveals that the VA1 strain was able to degrade PAHs in petroleum wastewater under saline conditions. The promising PAH-degrading halotolerant bacterial strain, VA1, was identified as Ochrobactrum sp. using biochemical and molecular techniques.

Thermophilic bacteria from Mexican thermal environments: isolation and potential applications

Extremophiles are microorganisms that possess application possibilities in several industrial fields, including agricultural, chemical, laundry, pharmaceutical, food, petroleum and bioremediation. This work reports the isolation of 19 thermophilic, alkalitolerant and halotolerant bacterial strains from two thermal sites in Veracruz, México: El Carrizal thermal pool and Los Baños hot spring. These strains belong to the Geobacillus, Anoxybacillus and Aeribacillus genera. The strains produce lipases, proteases, and amylases under thermophilic conditions. They may have good potential for application in microbial enhanced oil recovery, since they are thermophilic and halotolerant, produce exopolymers (up to 11.8 mg/mg) and acids, show emulsifying activity (E24 up to 7.5%), and are able to grow in kerosene as carbon source; these strains may also be used in biodesulphurization since they can grow in dibenzothiophene producing 2‐hydroxybiphenyl under thermophilic conditions (up to 2.9 mg/L).

Salinarimonas rosea gen. nov., sp. nov., a new member of the α-2 subgroup of the Proteobacteria

A Gram-negative, rod-shaped, facultatively anaerobic, halotolerant bacterial strain, designated YIM YD3(T), was isolated from a salt mine in Yunnan, south-west China. The taxonomy of strain YIM YD3(T) was investigated by a polyphasic approach. Strain YIM YD3(T) was motile, formed pink colonies and was positive for catalase and oxidase activities. Q-10 was the predominant respiratory ubiquinone. The major polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylmethylethanolamine, phosphatidylcholine and two unknown phospholipids. The major fatty acids (>10 % of total fatty acids) were C(18 : 1)omega7c, C(18 : 1)omega9c, C(16 : 0) and C(19 : 0) cyclo omega8c. The DNA G+C content was 71.8 mol%. Phylogenetic analysis based on 16S rRNA gene sequence comparisons showed that the isolate formed a distinct line within a clade containing the genera Balneimonas, Bosea, Chelatococcus and Microvirga in the order Rhizobiales, with highest levels of 16S RNA gene sequence similarity to the type strain of Balneimonas flocculans (93.5 %). On the basis of phenotypic, chemotaxonomic and phylogenetic data, strain YIM YD3(T) represents a novel species in a new genus, for which the name Salinarimonas rosea gen. nov., sp. nov. is proposed, with strain YIM YD3(T) (=KCTC 22346(T)=CCTCC AA208038(T)) as the type strain.

Isolation and characterization of culturable halophilic microorganisms of salt ponds in Lianyungang, China

The Lianyungang salt ponds are an extreme saline environment, and their microbial communities have not been characterized. A typical extreme halophilic archaeon strain designated as HBCC-2 (GenBank accession number: EF687739) was isolated from the salt ponds of Lianyungang in Jiangsu Province, P. R. China, using conventional microbial culture methods. The other halotolerant bacterial strain designated as HBCC-3 (GenBank accession number: EU377478) was isolated from the same sampling sites. The morphological and physiological characteristics of HBCC-2 and HBCC-3 were observed and examined. G+C content of HBCC-2 and HBCC-3 were determined using high-performance liquid chromatography. The cellular phospholipid fatty acids were analyzed using gas chromatography-mass spectrometry. The 16S rRNA gene sequences of the strains HBCC-2 and HBCC-3 were amplified by PCR using archaeal primers and bacterial primers, respectively. Homology of 16S rRNA gene sequences of the strains HBCC-2 and HBCC-3 were compared with the other similar sequences obtained from GenBank using the BLAST program. Phylogenetic analysis was performed using the software MEGA 4.0 after multiple alignments of sequence data using software CLUSTALW 1.8. The evolutional distances (by Kimura’s model) were calculated and the clusters were performed with the neighbor-joining method. The results showed that the 16S rRNA gene sequences of the strains HBCC-2 and HBCC-3 are related to the genera Halorubrum and Alkalibacillus, respectively. Two phylogenetic trees were constructed by phylogenetic analysis based on the 16S rRNA gene sequence. Based on the above results, the strains HBCC-2 and HBCC-3 were finally identified. The discovery of the two species provides an opportunity to further study these halophilic microorganisms in the Lianyungang salt ponds.

Isolation and characterization ofHalomonassp. strain C2SS100, a hydrocarbon-degrading bacterium under hypersaline conditions

To isolate and characterize an efficient hydrocarbon-degrading bacterium under hypersaline conditions, from a Tunisian off-shore oil field. Production water collected from 'Sercina' petroleum reservoir, located near the Kerkennah island, Tunisia, was used for the screening of halotolerant or halophilic bacteria able to degrade crude oil. Bacterial strain C2SS100 was isolated after enrichment on crude oil, in the presence of 100 g l(-1) NaCl and at 37 degrees C. This strain was aerobic, Gram-negative, rod-shaped, motile, oxidase + and catalase +. Phenotypic characters and phylogenetic analysis based on the 16S rRNA gene of the isolate C2SS100 showed that it was related to members of the Halomonas genus. The degradation of several compounds present in crude oil was confirmed by GC-MS analysis. The use of refined petroleum products such as diesel fuel and lubricating oil as sole carbon source, under the same conditions of temperature and salinity, showed that significant amounts of these heterogenic compounds could be degraded. Strain C2SS100 was able to degrade hexadecane (C16). During growth on hexadecane, cells surface hydrophobicity and emulsifying activity increased indicating the production of biosurfactant by strain C2SS100. A halotolerant bacterial strain Halomonas sp. C2SS100 was isolated from production water of an oil field, after enrichment on crude oil. This strain is able to degrade hydrocarbons efficiently. The mode of hydrocarbon uptake is realized by the production of a biosurfactant which enhances the solubility of hydrocarbons and renders them more accessible for biodegradation. The biodegradation potential of the Halomonas sp. strain C2SS100 gives it an advantage for possibly application on bioremediation of water, hydrocarbon-contaminated sites under high-salinity level.

Investigations on ultraviolet light and nitrous acid induced mutations of halotolerant bacterial strains for the treatment of tannery soak liquor

The objective of this research work is to study the effect of physical and chemical mutagenesis on biological treatment of tannery saline wastewater (soak liquor) employing halotolerant bacterial strains. Four halotolerant bacterial strains isolated from saline sources were used. The strains were identified as Pseudomonas aeruginosa, Bacillus flexus, Exiguobacterium homiense and Staphylococcus aureus, respectively. The isolates were found to grow well in medium containing 0–10% NaCl. At high saline concentration (>5%), the identified strains and their mixed consortia showed a low degrading efficiency of soak liquor (35–45%). UV light and nitrous acid mutagenesis were performed over the strains and the mutated strains were employed for degradation of soak liquor at high salinity level (6% by wt). Comparison of Chemical Oxygen Demand (COD) removal rates for both pure mutant isolates and mixed mutated consortia showed that nitrous acid mutagenesis resulted in degradation of 71% COD removal. Ultraviolet (UV) mutagenesis has no effect on degradation effectiveness. Biomass sludge (Mixed Liquor Volatile Suspended Solids) growth was also found to be high in nitrous acid treated strains.

Nutrient optimization for production of polyhydroxybutyrate from halotolerant photosynthetic bacteria cultivated under aerobic-dark condition

Three halotolerant bacterial strains; Rhodobacter sphaeroides ES16 (the wild type) and the two mutant strains of R. sphaeroides ES16, namely N20 and U7, were cultivated in glutamate-malate (GM) medium and screened for production of polyhydroxybutyrate (PHB). The mutant strains N20 and U7 were found to accumulate PHB (53.9 and 42.0% of DCW, respectively) 3.6 and 2.8 times higher than the wild type strain (19.5% of DCW), respectively. R. sphaeroides N20 were selected for studies on the effects of nutrient and environmental conditions on PHB accumulation. The optimal condition was 4 g/l acetate, 0.02 g/l (NH 4 ) 2 SO 4 , C/N ratio of 6:1, 1.0 g/l K 2 HPO 4 , 1.0 g/l KH 2 PO 4 and 3% NaCl with initial pH at 7.0. Under this optimal condition, the maximum PHB accumulation increased from 53.9% to 88% of DCW and 9.11 ± 0.08 g/l biomass, 8.02 ± 0.10 g/l PHB concentration were achieved after 60 hrs cultivation at 37oC. These results are the highest values ever obtained from photosynthetic bacteria reported so far.