Combined application of ascorbic acid and endophytic N-fixing Azotobacter chroococcum Avi2 modulates photosynthetic efficacy, antioxidants and growth-promotion in rice under moisture deficit stress.

This group has previously reported the role of ascorbic acid (AA) as an antioxidant for survivability and ability to enhancing diazotrophic efficacy in Azotobacter chroococcum Avi2 under hydrogen peroxide (H2O2) stress. However, the present study showed the combined application of AA and Avi2 in drought-susceptible (IR64 and Naveen) and drought-tolerant (Ankit and Satyabhama) rice cultivars to determine their photosynthetic efficacy (chlorophyll fluorescence-imaging), antioxidants, and plant growth-promotion (PGP) under moisture deficit stress (MS, -60 kPa). The results indicated that combined application of AA and Avi2 significantly (p < 0.05) increased the total chlorophyll, relative water content, electrolytic leakage, super oxide dismutase, and catalase activities in all rice cultivars as compared to other MS treatments, whereas stress indicators like proline and H2O2 contents were proportionally increased under MS and their concentration were normalized under combined application of AA and Avi2. Photochemical quenching, non-photochemical quenching, photosynthetic electron transport rate, and the effective quantum efficiency were found to be increased significantly (p < 0.05) in Avi2 + AA as compared to other MS treatments. Moreover, rice roots harbored significantly (p < 0.05) higher copy number of nifH gene in Avi2 + AA treatment followed by Avi2 compared to flooded control and other MS treatments. Combined application of AA and Avi2 also increased the grain yield significantly (p < 0.05) by 7.09 % and 3.92 % in drought-tolerant (Ankit and Satyabhama, respectively) and 31.70 % and 34.19 % in drought-susceptible (IR64 and Naveen, respectively) rice cultivars compared to MS treatment. Overall, the present study indicated that AA along with Avi2 could be an effective formulation to alleviate MS vis à vis enhances PGP traits in rice.

Bacterial inoculation positively affects the quality and quantity of flax under deficit irrigation regimes.

AIM: The present research was conducted to investigate the effect of plant growth-promoting rhizobacteria (PGPR) and deficit irrigation on quality and quantity of flax under field and pot conditions to determine bacterial efficiency and to decrease water deficit effects. METHODS AND RESULTS: Initially, in vitro experiments were performed to determine the growth-promoting characteristics of bacteria. Then in the field, the effects of bacterial inoculation (control, Azotobacter chroococcum, Azospirillum lipoferum, Bacillus amyloliquefaciens, Bacillus sp. strain1 and Pseudomonas putida) on flax traits were evaluated at different irrigation levels (100, 75 and 50% crop water requirement). Bacterial treatments in the pot experiment were selected based on the field experiment results. The irrigation regimes in the pot and field experiments were the same and bacterial treatments included single, doublet and triplet applications of the bacteria. All the bacterial strains could solubilize phosphate, produce ammonia (except for Bacillus sp. strain1), indole acetic acid and siderophore (except P. putida). Field results indicated that the bacteria significantly mitigated the effects of water deficit. Compared with control plants, bacterial treatments increased the oil, linolenic acid, protein and sulphur content; the number of shoots and capsules; and the harvest index in the flax plants. Pot experimental results revealed that the combined inoculations were more effective than single inoculum treatments. CONCLUSIONS: Bacterial inoculation alleviates deficit irrigation effects in flax plants. SIGNIFICANCE AND IMPACT OF THE STUDY: The effectiveness of applying A. chroococcum, B. amyloliquefaciens and Bacillus sp. strain1 was confirmed, especially as a combination to protect flax against water deficit and to improve its nutritional quality and growth.

Ascorbic acid formulation for survivability and diazotrophic efficacy of Azotobacter chroococcum Avi2 (MCC 3432) under hydrogen peroxide stress and its role in plant-growth promotion in rice (Oryza sativa L.).

Oxidative stress generates reactive oxygen species which causes cell damage of living organisms and are normally detoxified by antioxidants. Indirect reports signify the damages caused by reactive oxygen species and neutralized by antioxidant, but the direct evidence to confirm this hypothesis is still unclear. To validate our hypothesis, an attempt was made in a diazotrophic bacterium (Azotobacter chroococcum Avi2) as a biological system, and hydrogen peroxide (H2O2) and ascorbic acid were used as oxidative stress and antioxidant supplement, respectively. Additionally, rice plant-growth attributes by Avi2 was also assessed under H2O2 and ascorbic acid. Results indicated that higher concentration of H2O2 (2.5 mM-4.5 mM) showed the complete mortality of Avi2, whereas one ppm ascorbic acid neutralized the effect of H2O2. Turbidity, colony forming unit, DNA quantity, nifH gene abundance, indole acetic acid and ammonia productions were significantly (p < 0.5) increased by 11.93%, 17.29%, 19.80%, 74.77%, 71.89%, and 42.53%, respectively in Avi2-treated with 1.5 mM H2O2 plus ascorbic acid compared to 1.5 mM H2O2 alone. Superoxide dismutase was significantly (p < 0.5) increased by 60.85%, whereas catalase and ascorbate peroxidase activities were significantly (p < 0.05) decreased by 64.28% and 68.88% in Avi2-treated with 1.5 mM H2O2 plus ascorbic acid compared to 1.5 mM H2O2 alone. Germination percentage of three rice cultivars (FR13a, Naveen and Sahbhagi dhan) were significantly (p < 0.5) increased by 20%, 13.33%, and 4%, respectively in Avi2-treated with 0.6 mM H2O2 plus ascorbic acid compared with uninoculated control. Overall, this study indicated that ascorbic acid formulation neutralizes the H2O2-oxidative stress and enhances the survivability and plant growth-promoting efficacy of A. chroococcum Avi2 and therefore, it may be used as an effective formulation of bio-inoculants in rice under oxidative stress.

Trichoderma-Azotobacter biofilm inoculation improves soil nutrient availability and plant growth in wheat and cotton.

Microbial biofilms are gaining importance in agriculture, due to their multifaceted agronomic benefits and resilience to environmental fluctuations. This study focuses on comparing the influence of single inoculation-Azotobacter chroococcum (Az) or Trichoderma viride (Tv) and their biofilm (Tv-Az), on soil and plant metabolic activities in wheat and cotton grown under Phytotron conditions. Tv-Az proved superior to all the other treatments in terms of better colonisation, plant growth attributes and 10-40% enhanced availability of macronutrients and micronutrients in the soil, over control. Confocal and scanning electron microscopy showed that the cells attached to the root tips initially, followed by their proliferation along the surface of the roots. Soil polysaccharides, proteins and dehydrogenase activity showed several fold enhancement in Tv-Az biofilm inoculated samples. Time course studies revealed that the population of Az and Tv in the rhizoplane and rhizosphere was significantly higher with a 0.14-0.31 log colony-forming unit (CFU) increase in the biofilm-inoculated treatment in both crops. Enhancement in soil biological activities was facilitated by the improved colonisation of the biofilm, due to the synergistic association between Tv and Az. This demonstrates the utility of Tv-Az biofilm as a multifunctional plant growth promoting and soil fertility enhancing option in agriculture.

Microbial inoculants as plant growth stimulating and soil nutrient availability enhancing options for cucumber under protected cultivation.

Protected cultivation of vegetables is often hampered by declining nutrient availability in soil due to year-around farming, which in turn, leads to poor quality and yields, causing serious concern. Our study aimed towards evaluating the potential of novel biofilm formulations-Anabaena or Trichoderma as matrices with Azotobacter sp. as Anabaena-Azotobacter (An-Az) and Trichoderma-Azotobacter (Tr-Az) or together as Anabaena-Trichoderma (An-Tr), on the growth, physiological activities, yield, and changes in the profiles of soil microbial communities in two cultivars (cv. DAPC-6 and cv. Kian) of cucumber (Cucumis sativus). Photosynthetic pigments, evaluated as an index of growth showed two-threefold increase, while elicited activity of defense and antioxidant enzymes was stimulated; this facilitated significant improvement in the plants belonging to the inoculated treatments. Microbial biomass carbon and polysaccharides in soil enhanced by two-threefolds in treatments receiving microbial formulations. Available N in soil increased by 50-90% in An-Az and An-Tr biofilm inoculated treatments, while the availability of P and organic C content of soil improved by 40-60%, over control. PCR-DGGE profiles generated revealed signification modulation of cyanobacterial communities and cultivar-specific differences. Significant enhancement in leaf chlorophyll pigments, soil microbiological parameters and nutrient bio-availabilities along with positive correlation among the analysed parameters, and distinct profiles generated by PCR-DGGE analyses illustrated the promise of these novel inoculants for cucumber.

Root inoculation with Azotobacter chroococcum 76A enhances tomato plants adaptation to salt stress under low N conditions.

BACKGROUND: The emerging roles of rhizobacteria in improving plant nutrition and stress protection have great potential for sustainable use in saline soils. We evaluated the function of the salt-tolerant strain Azotobacter chroococcum 76A as stress protectant in an important horticultural crop, tomato. Specifically we hypothesized that treatment of tomato plants with A. chroococcum 76A could improve plant performance under salinity stress and sub-optimal nutrient regimen. RESULTS: Inoculation of Micro Tom tomato plants with A. chroococcum 76A increased numerous growth parameters and also conferred protective effects under both moderate (50 mM NaCl) and severe (100 mM NaCl) salt stresses. These benefits were mostly observed under reduced nutrient regimen and were less appreciable in optimal nitrogen conditions. Therefore, the efficiency of A. chroococcum 76A was found to be dependent on the nutrient status of the rhizosphere. The expression profiles of LEA genes indicated that A. chroococcum 76A treated plants were more responsive to stress stimuli when compared to untreated controls. However, transcript levels of key nitrogen assimilation genes revealed that the optimal nitrogen regimen, in combination with the strain A. chroococcum 76A, may have saturated plant's ability to assimilate nitrogen. CONCLUSIONS: Roots inoculation with A. chroococcum 76A tomato promoted tomato plant growth, stress tolerance and nutrient assimilation efficiency under moderate and severe salinity. Inoculation with beneficial bacteria such as A. chroococcum 76A may be an ideal solution for low-input systems, where environmental constraints and limited chemical fertilization may affect the potential yield.

Influence of l-amino acids on aggregation and biofilm formation in Azotobacter chroococcum and Trichoderma viride.

AIM: The effects of l-amino acids on growth and biofilm formation in Azotobacter chroococcum (Az) and Trichoderma viride (Tv) as single (Az, Tv) and staggered inoculated cultures (Az-Tv, Tv-Az) were investigated. METHODS AND RESULTS: A preliminary study using a set of 20 l-amino acids, identified 6 amino acids (l-Glu, l-Gln, l-His, l-Ser, l-Thr and l-Trp) which significantly enhanced growth and biofilm formation. Supplementation of these amino acids at different concentrations revealed that 40 mmol l-1 was most effective. l-Glu and l-Gln favoured planktonic growth in both single and in staggered inoculated cultures, while l-Trp and l-Thr, enhanced aggregation and biofilm formation. Addition of l-Glu or l-Gln increased carbohydrate content and planktonic population. Principal component analysis revealed the significant role of proteins in growth and biofilm formation, particularly with supplementation of l-Trp, l-Thr and l-Ser. Azotobacter was found to function better as biofilm under staggered inoculated culture with Trichoderma. CONCLUSIONS: The results illustrate that amino acids play crucial roles in microbial biofilm formation, by influencing growth, aggregation and carbohydrates synthesized. SIGNIFICANCE AND IMPACT OF THE STUDY: The differential and specific roles of amino acids on biofilm formation are of significance for agriculturally important micro-organisms that grow as biofilms, colonize and benefit the plants more effectively.

Compatibility of Azospirillum brasilense and Pseudomonas fluorescens in growth promotion of groundnut ( Arachis hypogea L)

ABSTRACT We attempted to study the compatibility among plant beneficial bacteria in the culture level by growing them near in the nutrient agar plates. Among all the bacteria tested, Rhizobium was found to inhibit the growth of other bacteria. From the compatible group of PGPR, we have selected one biofertilizer (Azospirillum brasilense strain TNAU) and one biocontrol agent (Pseudomonas fluorescens strain PF1) for further studies in the pot culture. We have also developed a bioformulation which is talc powder based, for individual bacteria and mixed culture. This formulation was used as seed treatment, soil application, seedling root dip and foliar spray in groundnut crop in vitro germination conditions. A. brasilense was found to enhance the tap root growth and P. fluorescens, the lateral root growth. The other growth parameters like shoot growth, number of leaves were enhanced by the combination of both of the bacteria than their individual formulations. Among the method of application tested in our study, soil application was found to be the best in yielding better results of plant growth promotion.

Compatibility of Azospirillum brasilense and Pseudomonas fluorescens in growth promotion of groundnut ( Arachis hypogea L.).

We attempted to study the compatibility among plant beneficial bacteria in the culture level by growing them near in the nutrient agar plates. Among all the bacteria tested, Rhizobium was found to inhibit the growth of other bacteria. From the compatible group of PGPR, we have selected one biofertilizer (Azospirillum brasilense strain TNAU) and one biocontrol agent (Pseudomonas fluorescens strain PF1) for further studies in the pot culture. We have also developed a bioformulation which is talc powder based, for individual bacteria and mixed culture. This formulation was used as seed treatment, soil application, seedling root dip and foliar spray in groundnut crop in vitro germination conditions. A. brasilense was found to enhance the tap root growth and P. fluorescens, the lateral root growth. The other growth parameters like shoot growth, number of leaves were enhanced by the combination of both of the bacteria than their individual formulations. Among the method of application tested in our study, soil application was found to be the best in yielding better results of plant growth promotion.

Microbial Nitrogen-Cycle Gene Abundance in Soil of Cropland Abandoned for Different Periods.

In Inner Mongolia, steppe grasslands face desertification or degradation because of human overuse and abandonment after inappropriate agricultural management. The soils in these abandoned croplands exist in heterogeneous environments characterized by widely fluctuating microbial growth. Quantitative polymerase chain reaction analysis of microbial genes encoding proteins involved in the nitrogen cycle was used to study Azotobacter species, nitrifiers, and denitrifiers in the soils from steppe grasslands and croplands abandoned for 2, 6, and 26 years. Except for nitrifying archaea and nitrous oxide-reducing bacteria, the relative genotypic abundance of microbial communities involved in nitrogen metabolism differed by approximately 2- to 10-fold between abandoned cropland and steppe grassland soils. Although nitrogen-cycle gene abundances varied with abandonment time, the abundance patterns of nitrogen-cycle genes separated distinctly into abandoned cropland versus light-grazing steppe grassland, despite the lack of any cultivation for over a quarter-century. Plant biomass and plant diversity exerted a significant effect on the abundance of microbial communities that mediate the nitrogen cycle (P < 0.002 and P < 0.03, respectively). The present study elucidates the ecology of bacteria that mediate the nitrogen cycle in recently abandoned croplands.

Interaction of Piriformospora indica with Azotobacter chroococcum.

Microbial communities in rhizosphere interact with each other and form a basis of a cumulative impact on plant growth. Rhizospheric microorganisms like Piriformospora indica and Azotobacter chroococcum are well known for their beneficial interaction with plants. These features make P. indica/A. chroococcum co-inoculation of crops most promising with respect to sustainable agriculture and to understanding the transitions in the evolution of rhizospheric microbiome. Here, we investigated interactions of P. indica with A. chroococcum in culture. Out of five Azotobacter strains tested, WR5 exhibited growth-promoting while strain M4 exerted growth-inhibitory effect on the fungus in axenic culture. Electron microscopy of co-culture indicated an intimate association of the bacterium with the fungus. 2-D gel electrophoresis followed by mass spectrometry of P. indica cellular proteins grown with or without WR5 and M4 showed differential expression of many metabolic proteins like enolase-I, ureaseD, the GTP binding protein YPT1 and the transmembrane protein RTM1. Fungal growth as influenced by bacterial crude metabolites was also monitored. Taken together, the results conform to a model where WR5 and M4 influence the overall growth and physiology of P. indica which may have a bearing on its symbiotic relationship with plants.

Plant growth promotion rhizobacteria in onion production.

The aim of the research was to examine the effect of rhizospheric bacteria Azotobacter chroococcum, Pseudomonas fluorescens (strains 1 and 2) and Bacillus subtilis on the growth and yield of onion and on the microorganisms in the rhizosphere of onion. The ability of microorganisms to produce indole-acetic acid (IAA), siderophores and to solubilize tricalcium phosphate (TCP) was also assessed. The experiment was conducted in field conditions, in chernozem type of soil. Bacillus subtilis was the best producer of IAA, whereas Pseudomonas fluorescens strains were better at producing siderophores and solubilizing phosphates. The longest seedling was observed with the application of Azotobacter chroococcum. The height of the plants sixty days after sowing was greater in all the inoculated variants than in the control. The highest onion yield was observed in Bacillus subtilis and Azotobacter chroococcum variants. The total number of bacteria and the number of Azotobacter chroococcum were larger in all the inoculated variants then in the control. The number of fungi decreased in most of the inoculated variants, whereas the number of actinomycetes decreased or remained the same.

Compensation effect of bacterium containing biofertilizer on the growth of Cucumis sativus L. under Al-stress conditions.

Biofertilizers are used to improve soil fertility and plant production in sustainable agriculture. However, their applicability depends on several environmental parameters. The aim of our study was to evaluate the effect of free-living bacteria containing fertilizer on the growth of cucumber (Cucumis sativus L. cvs. Delicates) under aluminium (Al) stress. Different responses to Al stress of cucumber growth parameters were examined in terms of root elongation and physiological traits, such as Spad index (relative chlorophyll value), biomass accumulation of root and shoot, Al uptake and selected element contents (Fe, Mn, Zn, Mg) of leaves and root. The applied bacteria containing biofertilizer contains Azotobacter chroococcum and Bacillus megaterium. The dry weights of cucumber shoots and roots decreased in line with the increasing Al concentration. Due to different Al treatments (10-3 M, 10-4 M) higher Al concentration was observed in the leaves, while the amounts of other elements (Fe, Mn, Zn, Mg) decreased. This high Al content of the leaves decreased below the control value when biofertilizer was applied. In the case of the roots the additional biofertilizer treatments compensated the effect of Al. The relative chlorophyll content was reduced during Al-stress in older plants and the biofertilizer moderated this effect. The root/shoot ratio was decreased in all the Al-treatments in comparison to the control. The living bacteria containing fertilizer also had a modifying effect. The root/shoot ratio increased at the 10-4 M Al2(SO4)2 + biofertilizer and 10-4 M Al(NO3)3 + biofertilizer treatments compared to the control and Al-treatments. According to our results the biofertilizer is an alternative nutrient supply for replacing chemical fertilizers because it enhances dry matter production. Biofertilizer usage is also offered under Al polluted environmental conditions. Although, the nutrient solution is a clean system where we can examine the main processes without other effects of natural soils. The soil can modify the results, e.g. the soil-born microorganisms affect nutrient availability, and also can modify the harmful effects of different heavy metals. The understanding of basic processes will help us to know more about the soil behaviour.

Effectiveness of Azotobacter bio-inoculant for wheat grown under dryland condition.

Judicious use of chemicals along with biofertilizers and organic resources are advocated for sustaining crop productivity and soil health, and meeting a part of fertilizer requirement for different crops. In the present study, different combinations of nitrogen (urea and/or farmyard manure) doses with Azotobacter strain (Azo-8) were experimented for a dryland wheat variety GW-273. It was observed that the combination of Azotobacter strain (Azo-8) along with urea (60KgN ha-1) and farm yard manure (40KgN ha -1) gave the best response. It resulted in more than 23% and 36% increase in shoot fresh weight and dry weight, 26% and 38% increase in root fresh weight and dry weight, 39% increase in test weight of seeds and 27% increase in yield over control. The results of present experiments can be utilized in integrated nutrient management for wheat cultivation in dryland areas to provide sustainability to the agricultural productivity.

Response of soybean to seed inoculation with Bradyrhizobium japonicum and with mixed inoculants of B. japonicum and Azotobacter chroococcum.

Effects of pre-sowing soybean seed inoculation with Bradyrhizobium japonicum alone or with mixed inoculants containing soybean rhizobia and Azotobacter chroococcum were compared. In the pot experiment all the tested strains of soybean rhizobia in pure cultures or in mixtures with A. chroococcum significantly improved nodulation of soybean plants and seed yields of this crop. In micro-plot experiments pre-sowing soybean seeds treatment with the inoculant containing the most effective strain 94P of B. japonicum alone or with the mixed inoculant of strain 94P and A. chroococcum were equally effective in improving nodulation intensity and seed yields of soybean in comparison to the uninoculated soybean.

Efecto biofertilizante del preparado: residuos vegetales - bacteria nativa diazótrofa, sobre las variables biométricas en plántulas de Rhapanus sativus / Biofertilizer effect of the prepared from vegetales wastes - diazotroph native bacterium on biometrics variables of Rhapanus sativus seedlings

El uso de bioinoculantes a base de microorganismos con potencial biofertilizante representa una alternativa económicamente viable y de producción limpia para el sector agrícola. El objetivo del presente trabajo fue evaluar el efecto biofertilizante de un preparado elaborado con residuos sólidos vegetales (RSV) procedentes del mercado y la bacteria nativa diazótrofa Azotobacter A15M2G. Se elaboraron biopreparados utilizando diferentes concentraciones de bacteria (106, 107 y 108 UFC) en un medio de cultivo obtenido a partir del 25% p/v de cada uno de los siguientes RSV: Brassica oleracea (repollo), Lactuca sativa (lechuga) y Allium fistulosum (cebollín). Los biopreparados fueron evaluados en plantas de rábano (Rhapanus sativus) en invernadero, utilizando un diseño estadístico completamente al azar de 5 tratamientos con 3 repeticiones: T1, control; T2, semillas pregerminadas tratadas con RSV al 25% p/v; T3, semillas pregerminadas con bioinoculante de 106 UFC; T4, semillas pregerminadas con bioinoculante de 107 UFC; T5, semillas pregerminadas con bioinoculante de 108 UFC. Se evaluó: número de hojas, área foliar, longitud de la planta, longitud de la raíz y peso seco de toda la planta (ensayos por triplicado). Se observó un incremento altamente significativo en peso seco para T5 (0,88 g) y T4 (1,10 g); y diferencias significativas en el área foliar, para los mismos tratamientos, con un valor superior a 2000 cm2. El biopreparado con bacterias nativas y RSV mejoró el crecimiento y desarrollo de las plantas de rábano, pudiéndose dar un valor agregado a estos residuos y de esta manera obtener un biofertilizante potencialmente utilizable en otros cultivos.

The use of bioinoculantes from microorganisms with biofertilizer potential, represents an economically viable alternative and of clean production for the agricultural sector. The aim of this study was to evaluate the effect of biofertilizer preparation obtained from vegetable solid waste (RSV) of the market and the native bacteria Azotobacter A15M2G diazotroph.Biological cultures were prepared using different inoculum concentrations, 106, 107 y 108 UFC in a culture medium obtained from 25% w / v of each of the following substrates: Brassica oleracea (cabbage), Lactuca sativa (lettuce) and Allium fistulosum (chives). The microbial inoculants were evaluated in radish plants (Rhapanus sativus) in greenhouse using a completely randomized design of 5 treatments with 3 replicates: T1, pre-germinated seeds without any treatment; T2, pre-germinated seeds treated with the dye waste vegetables 25% w / v; T3, pre-germinated seeds treated with bacterial concentration bioinoculants to 106 UFC; T4, pre-germinated seeds treated with bacterial concentration bioinoculants to 107 UFC, and T5, pre-germinated seeds treated with bacterial concentration bioinoculants to 108 UFC. Assessed variables were: number of leaves, leaf area, plant length, root length and dry weight of the entire plant (all assays in triplicate). The results showed a highly significant increase in dry weight, for T5 (0.88 g) and T4(1.10 g); and significant differences in leaf area for the same treatments, with a value greater than 2000 cm2, compared to others. The biopreparado from native bacteria and RSV improved the growth and development of the radish plants, being able to give a added value to these residues and to obtain a potentially usable biofertilizer in other cultures.

Artificial tripartite symbiosis involving a green alga (Chlamydomonas), a bacterium (Azotobacter) and a fungus (Alternaria): morphological and physiological characterization.

A long-living artificial tripartite symbiosis involving a green alga (Chlamydomonas), a bacterium (Azotobacter) and a fungus (Alternaria) was established on carbon- and nitrogen-free medium. The basis of the interdependence is the complementation of photosynthetic CO2 assimilation and atmospheric nitrogen fixation. Green color of the colonies indicated that the algal cells had enough nitrogen to synthesize chlorophylls. The chlorophyll content was nearly 40% of the control cells. The relatively high rate of photosynthetic oxygen evolution proved that nitrogen was effectively used for building up a well functioning photosynthetic apparatus. This was supported by the analysis of photosystems and ultrastructural investigations. In comparison with degreened algae cultured on nitrogen-free medium, the chloroplasts in the symbiont algal cells contained a well-developed, stacked thylakoid membrane system without extreme starch or lipid accumulation. The occurrence of the fungus in the association greatly increased the chlorophyll content. Far fewer types of amino acids were excreted by the tripartite cultures than by pure cultures. Cystathionine, which is a common intermediate in the sulfur-containing amino acid metabolism, was produced in high quantities by the tripartite symbiosis. This can mostly be attributed to the activity of the fungus.

NifH-based studies on azotobacterial diversity in cotton soils of India.

In order to promote the use of Azotobacter inoculants for cotton crop, a complete characterization of soil isolates of Azotobacter, isolated and screened on the basis of physiological properties, from four different cotton-wheat cropping regions of India was carried out, and their genetic diversity determined by RFLP (restriction fragment length polymorphism) analysis of the functional gene nifH. Genetic analysis of these isolates depicted a similarity coefficient of > or = 80% among them, suggesting that though the isolates were obtained from different cotton soils of India, still they have large commonality in the nifH gene and constituted a homogeneous nifH population.

[Evaluation of thermal resistance of Azotobacter chroococcum 66 using atomic force microscopy].

A possibility to use atomic force microscopy (AFM) for comparative analysis of thermal resistance of Azotobacter chroococcum 66 cells has been studied. The sizes of bacteria cells and the structuredness of the cytoderm have been shown to vary depending on the dose of hyperthermic action and on the composition of the media for heating and subsequent incubation. A thermally induced increase of a standard roughness parameter (R(a)) and of cell sizes has been revealed to reflect an increased level of their resistance to hyperthermia.

Biosurfactant production by Azotobacter chroococcum isolated from the marine environment.

Preliminary characterization of a biosurfactant-producing Azotobacter chroococcum isolated from marine environment showed maximum biomass and biosurfactant production at 120 and 132 h, respectively, at pH 8.0, 38 degrees C, and 30 per thousand salinity utilizing a 2% carbon substrate. It grew and produced biosurfactant on crude oil, waste motor lubricant oil, and peanut oil cake. Peanut oil cake gave the highest biosurfactant production (4.6 mg/mL) under fermentation conditions. The biosurfactant product emulsified waste motor lubricant oil, crude oil, diesel, kerosene, naphthalene, anthracene, and xylene. Preliminary characterization of the biosurfactant using biochemical, Fourier transform infrared spectroscopy, and mass spectral analysis indicated that the biosurfactant was a lipopeptide with percentage lipid and protein proportion of 31.3:68.7.