Differential effects of rhizobacteria from uninfected and infected tomato on Meloidogyne incognita under protected cultivation.

Intermingled uninfected and root-knot nematode-infected tomato plants are commonly observed under protected cultivation. To understand the role of rhizobacteria underlying the susceptibility to nematode infectivity in these tomato plants, 36 rhizobacteria (18 from each type) with morphologically distinct colony characteristics were isolated from the rhizosphere of uninfected and root-knot nematode-infected tomato plants. The in vitro nematicidal potential of rhizobacteria from the uninfected rhizosphere was significantly higher than that from the infested rhizosphere. The three most effective antagonists were identified as Microbacterium laevaniformans, Staphylococcus kloosii, Priestia aryabhattai from root-knot-nematode-infected tomato rhizosphere and Staphylococcus sciuri, Bacillus pumilus, and Priestia megaterium from the rhizosphere of uninfected tomato. Volatile organic compounds from these rhizobacteria were characterized. Except for S. kloosi, the soil drenching with other rhizobacteria significantly reduced juvenile penetration (>60%) in tomato roots. Furthermore, the application of a single or consortium of these rhizobacteria affected nematode reproduction in tomato. Four consortia of rhizobacteria (S. sciuri + B. pumilus + P. megaterium), (B. pumilus + P. megaterium), (S. sciuri + B. pumilus), and (S. sciuri + P. megaterium) from uninfested rhizosphere and two consortia (M. laevaniformans + P. aryabhattai), (M. laevaniformans + S. kloosii + P. aryabhattai) from infested rhizosphere (IRh) effectively reduced M. incognita reproduction and considerably enhanced plant growth and yield in tomato. The nematicidal efficacy, however, decreased when S. kloosii was applied in the consortium. These distinctive effects illustrate how the plant susceptibility to nematode infectivity is modulated under natural conditions.

Mycorrhizae Helper Bacteria: Unlocking Their Potential as Bioenhancers of Plant-Arbuscular Mycorrhizal Fungal Associations.

The dynamic interactions of plants and arbuscular mycorrhizal fungi (AMF) that facilitate the efficient uptake of minerals from soil and provide protection from various environmental stresses (biotic and abiotic) are now also attributed to a third component of the symbiosis. These are the less investigated mycorrhizae helper bacteria (MHB), which constitute a dense, active bacterial community, tightly associated with AMF, and involved in the development and functioning of AMF. Although AMF spores are known to host several bacteria in their spore walls and cytoplasm, their role in promoting the ecological fitness and establishment of AMF symbiosis by influencing spore germination, mycelial growth, root colonization, metabolic diversity, and biocontrol of soil borne diseases is now being deciphered. MHB also promote the functioning of arbuscular mycorrhizal symbiosis by triggering various plant growth factors, leading to better availability of nutrients in the soil and uptake by plants. In order to develop strategies to promote mycorrhization by AMF, and particularly to stimulate the ability to utilize phosphorus from the soil, there is a need to decipher crucial metabolic signalling pathways of MHB and elucidate their functional significance as mycorrhiza helper bacteria. MHB, also referred to as AMF bioenhancers, also improve agronomic efficiency and formulations using AMF along with enriched population of MHB are a promising option. This review covers the aspects related to the specificity and mechanisms of action of MHB, which positively impact the formation and functioning of AMF in mycorrhizal symbiosis, and the need to advocate MHB as AMF bioenhancers towards their inclusion in integrated nutrient management practices in sustainable agriculture.

Influence of cyanobacterial inoculants, elevated carbon dioxide, and temperature on plant and soil nitrogen in soybean.

Climate change affects nitrogen dynamics in crops and diazotrophic microorganisms with carbon dioxide (CO2 ) sequestering potential such as cyanobacteria can be promising options. The interactions of three cyanobacterial formulations (Anabaena laxa, Calothrix elenkinii and Anabaena torulosa-Bradyrhizobium japonicum biofilm) on plant and soil nitrogen in soybean, were investigated under elevated CO2 and temperature conditions. Soybean plants were grown inside Open Top Chambers under ambient and elevated (550 ± 25 ppm) CO2 concentrations and elevated temperature (+2.5-2.8°C). Interactive effect of elevated CO2 and cyanobacterial inoculation through A. laxa and Anabaena torulosa-B. japonicum biofilm led to improved growth, yield, nodulation, nitrogen fixation, and seed N in soybean crop. Nitrogenase activity in nodules increased in A. laxa and biofilm treatments, with an increase of 55% and 72%, respectively, over no cyanobacterial inoculation treatment. Although high temperature alone reduced soil microbial biomass carbon, dehydrogenase activity, and soil available N, the combined effect of CO2 and temperature were stimulatory; cyanobacterial inoculation further led to an increase under all the conditions. The highest seed N uptake (758 mg plant-1 ) was recorded with cyanobacterial biofilm inoculation under elevated CO2 with control temperature conditions. The positive interactions of elevated CO2 and cyanobacterial inoculation, particularly through A. laxa and A. torulosa-B. japonicum biofilm inoculation highlights their potential in counteracting the negative impact of changing climate along with enhancing plant and soil N in soybean.

Prospecting the significance of methane-utilizing bacteria in agriculture.

Microorganisms act as both the source and sink of methane, a potent greenhouse gas, thus making a significant contribution to the environment as an important driver of climate change. The rhizosphere and phyllosphere of plants growing in natural (mangroves) and artificial wetlands (flooded agricultural ecosystems) harbor methane-utilizing bacteria that oxidize methane at the source and reduce its net flux. For several decades, microorganisms have been used as biofertilizers to promote plant growth. However, now their role in reducing net methane flux, especially from flooded agricultural ecosystems is gaining momentum globally. Research in this context has mainly focused on taxonomic aspects related to methanotrophy among diverse bacterial genera, and environmental factors that govern methane utilization in natural and artificial wetland ecosystems. In the last few decades, concerted efforts have been made to develop multifunctional microbial inoculants that can oxidize methane and alleviate greenhouse gas emissions, as well as promote plant growth. In this context, combinations of taxonomic groups commonly found in rice paddies and those used as biofertilizers are being explored. This review deals with methanotrophy among diverse bacterial domains, factors influencing methane-utilizing ability, and explores the potential of novel methane-utilizing microbial consortia with plant growth-promoting traits in flooded ecosystems.

Cyanobacterial inoculation as resource conserving options for improving the soil nutrient availability and growth of maize genotypes.

Harnessing the benefits of plant-microbe interactions towards better nutrient mobilization and plant growth is an important challenge for agriculturists globally. In our investigation, the focus was towards analyzing the soil-plant-environment interactions of cyanobacteria-based formulations (Anabaena-Nostoc consortium, BF1-4 and Anabaena-Trichoderma biofilm, An-Tr) as inoculants for ten maize genotypes (V1-V10). Field experimentation using seeds treated with the formulations illustrated a significant increase of 1.3- to 3.8-fold in C-N mobilizing enzyme activities in plants, along with more than five- to six-fold higher values of nitrogen fixation in rhizosphere soil samples. An increase of 22-30% in soil available nitrogen was also observed at flag leaf stage, and 13-16% higher values were also recorded in terms of cob yield of V6 with An-Tr biofilm inoculation. Savings of 30 kg N ha-1 season-1 was indicative of the reduced environmental pollution, due to the use of microbial options. The use of cyanobacterial formulations also enhanced the economic, environmental and energy use efficiency. This was reflected as 37-41% reduced costs lowered GHG emission by 58-68 CO2 equivalents and input energy requirement by 3651-4296 MJ, over the uninoculated control, on hectare basis. This investigation highlights the superior performance of these formulations, not only in terms of efficient C-N mobilization in maize, but also making maize cultivation a more profitable enterprise. Such interactions can be explored as resource-conserving options, for future evaluation across ecologies and locations, particularly in the global climate change scenario.

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.

Interplay of phosphorus doses, cyanobacterial inoculation, and elevated carbon dioxide on yield and phosphorus dynamics in cowpea.

Phosphorus (P) demand is likely to increase especially in legumes to harness greater benefits of nitrogen fixation under elevated CO2 condition. In the following study, seed yield and seed P uptake in cowpea increased by 26.8% and 20.9%, respectively, under elevated CO2 level. With an increase in phosphorus dose up to 12 mg kg-1, seed yield enhanced from 2.6 to 5.4 g plant-1. P application and cyanobacterial inoculation increased the microbial activity of soil, leading to increased availability of P. Under elevated CO2 condition, microbial activity, measured as dehydrogenase, acid phosphatase, and alkaline phosphatase activities showed stimulation. Soil available P also increased under elevated CO2 condition and was stimulated by both P application and cyanobacterial inoculation. Higher P uptake in elevated CO2 condition led to lower values of inorganic P in soil. Stepwise regression analysis showed that aboveground P uptake, soil available P, and alkaline phosphatase activity of soil influenced the yield while available P, and organic and inorganic P influenced the aboveground P uptake of the crop. This study revealed that under elevated CO2 condition, P application and cyanobacterial inoculation facilitated P uptake and yield, mediated through enhanced availability of nutrients, in cowpea crop.

Interactive effects of Magnaporthe inoculation and nitrogen doses on the plant enzyme machinery and phyllosphere microbiome of resistant and susceptible rice cultivars.

Severity of plant diseases is often influenced by the availability of nutrients, particularly N; however, its effect on the phyllosphere microbiome in foliar pathogen challenged plants is less investigated in rice. The tripartite interaction among the fungal pathogen (Magnaporthe oryzae), rice cultivars (basmati and non-basmati, blast resistant or susceptible) and nitrogen (N) fertilization (0, 120 and 180 N) was investigated. Plant growth, elicitation of defense responses and abundance of microbial members in the rice phyllosphere were monitored using biochemical and molecular methods. In general, photosynthetic pigments were distinct for each cultivar, and optimal N doses led to higher values. The susceptible var. CO-39 and resistant CO-39I exhibited higher contents of photosynthetic pigments and micronutrients such as zinc in leaves in response to N doses. Elicitation of defense and hydrolytic enzymes was significantly influenced by pathogen inoculation and modulated by N doses, but varietal effects were distinct. Scoring indices emphasized the pathogen susceptibility of var. CO-39 and PB-1, which showed almost 40-60% higher values than the resistant cultivars; the interactions of cultivars and N doses was also significant. Characteristic changes were recorded in the abundances of the gene copies, particularly, with an overall increase in the number of cyanobacterial 16S rRNA, and bacterial amoA in pathogen-challenged treatments, while nifH gene copies exhibited a reducing trend with increasing N doses, in the presence or absence of pathogen. The varietal differences in the cause and effect relationships can be valuable in crop protection for more effective foliar application of pesticides or biocontrol agents.

Influence of fertilizers and rice cultivation methods on the abundance and diversity of phyllosphere microbiome.

Rice paddies are man-made, cross-over ecologies of aquatic and terrestrial systems, which favor the proliferation of characteristic microbial communities. Moisture regimes under flooded and different levels of irrigation such as in direct seeded rice (DSR) and system of rice intensification (SRI) lead to modulation in crop physiology, soil nutrient availability, and the soil microbiome. However, the diversity of the rice phyllosphere microbiome is less investigated in terms of the influence of fertilizer application and the method of rice cultivation (conventional-flooded, DSR and SRI). Scanning electron micrographs revealed the presence of bacteria as aggregates at microsites of the leaves. Phylogenetic analysis of the dominant culturable bacterial isolates using 16S rDNA sequences revealed that they belonged to the genera - Bacillus, Brevibacillus, Pantoea, Enterobacter, Pseudomonas, Erwinia, and Streptomyces. Fertilizer application brought about a distinct modulation in the communities belonging to phyla such as Bacteriodetes, Firmicutes, and Planctomyces, besides Proteobacteria. The cyanobacterial population was much influenced by the cultivation methods, particularly the SRI. Principal component analysis (PCA), involving the culturable phyllospheric microbial groups and leaf attributes (nutrients and pigments), illustrated the importance of leaf nitrogen and zinc. Also, the communities of the phylum Firmicutes exhibited marked changes in terms of the diversity, not only due to the cultivation method, but also the application of fertilizers. Thus, the cultivation methods and fertilizer application played important roles in modulating both the structural (taxonomical) and functional attributes of the phyllosphere microbiome.

Cyanobacterial and rhizobial inoculation modulates the plant physiological attributes and nodule microbial communities of chickpea.

The present investigation aimed to understand the influence of two plant growth promoting cyanobacterial formulations (Anabaena-Mesorhizobium ciceri biofilm and Anabaena laxa), along with Mesorhizobium ciceri, on the symbiotic performance of five each of desi- and kabuli-chickpea cultivars. Inoculation with cyanobacterial formulations led to significant interactions with different cultivars, in terms of fresh weight and number of nodules, the concentration of nodular leghemoglobin, and the number of pods. The inoculant A. laxa alone was superior in its performance, recording 30-50% higher values than uninoculated control, and led to significantly higher nodule number per plant and fresh root weight, relative to the M. ciceri alone. Highest nodule numbers were recorded in the kabuli cultivars BG256 and BG1003. The kabuli cultivar BG1108 treated with the biofilmed Anabaena-M. ciceri inoculant recorded the highest concentration of leghemoglobin in nodules. These inoculants also stimulated the elicitation of defense- and pathogenesis-related enzymes in both the desi and kabuli cultivars, by two to threefolds. The analyses of Denaturing Gradient Gel Electrophoresis (DGGE) profiles revealed that microbial communities in nodules were highly diverse, with about 23 archaeal, 9 bacterial, and 13 cyanobacterial predominant phylotypes observed in both desi and kabuli cultivars, and influenced by the inoculants. Our findings illustrate that the performance of the chickpea plants may be significantly modulated by the microbial communities in the nodule, which may contribute towards improved plant growth and metabolic activity of nodules. This emphasizes the promise of cyanobacterial inoculants in improving the symbiotic performance of chickpea.

Agriculturally important microbial biofilms: Present status and future prospects.

Microbial biofilms are a fascinating subject, due to their significant roles in the environment, industry, and health. Advances in biochemical and molecular techniques have helped in enhancing our understanding of biofilm structure and development. In the past, research on biofilms primarily focussed on health and industrial sectors; however, lately, biofilms in agriculture are gaining attention due to their immense potential in crop production, protection, and improvement. Biofilms play an important role in colonization of surfaces - soil, roots, or shoots of plants and enable proliferation in the desired niche, besides enhancing soil fertility. Although reports are available on microbial biofilms in general; scanty information is published on biofilm formation by agriculturally important microorganisms (bacteria, fungi, bacterial-fungal) and their interactions in the ecosystem. Better understanding of agriculturally important bacterial-fungal communities and their interactions can have several implications on climate change, soil quality, plant nutrition, plant protection, bioremediation, etc. Understanding the factors and genes involved in biofilm formation will help to develop more effective strategies for sustainable and environment-friendly agriculture. The present review brings together fundamental aspects of biofilms, in relation to their formation, regulatory mechanisms, genes involved, and their application in different fields, with special emphasis on agriculturally important microbial biofilms.

Development of Mesorhizobium ciceri-Based Biofilms and Analyses of Their Antifungal and Plant Growth Promoting Activity in Chickpea Challenged by Fusarium Wilt.

Biofilmed biofertilizers have emerged as a new improved inoculant technology to provide efficient nutrient and pest management and sustain soil fertility. In this investigation, development of a Trichoderma viride-Mesorhizobium ciceri biofilmed inoculant was undertaken, which we hypothesized, would possess more effective biological nitrogen fixing ability and plant growth promoting properties. As a novel attempt, we selected Mesorhizobium ciceri spp. with good antifungal attributes with the assumption that such inoculants could also serve as biocontrol agents. These biofilms exhibited significant enhancement in several plant growth promoting attributes, including 13-21 % increase in seed germination, production of ammonia, IAA and more than onefold to twofold enhancement in phosphate solubilisation, when compared to their individual partners. Enhancement of 10-11 % in antifungal activity against Fusarium oxysporum f. sp. ciceri was also recorded, over the respective M. ciceri counterparts. The effect of biofilms and the M. ciceri cultures individual on growth parameters of chickpea under pathogen challenged soil illustrated that the biofilms performed at par with the M. ciceri strains for most plant biometrical and disease related attributes. Elicitation of defense related enzymes like l-phenylalanine ammonia lyase, peroxidase and polyphenol oxidase was higher in M. ciceri/biofilm treated plants as compared to uninoculated plants under pathogen challenged soil. Further work on the signalling mechanisms among the partners and their tripartite interactions with host plant is envisaged in future studies.

Taxonomic and functional diversity of the culturable microbiomes of epigeic earthworms and their prospects in agriculture.

Eisenia foetida and Perionyx excavatus are potent vermicomposting earthworms having immense importance in organic matter recycling under tropical conditions, particularly in India. Comparative assessment of the cultivable gut microbiome of these two epigeic earthworms after growth on lignocellulosic biomass, revealed populations of 3.2-8.3 × 10(9) CFU. Diversity analyses using 16S rDNA sequences revealed that the major dominating classes were Firmicutes (50-60%), followed by Actinobacteria (26.7-33%), and Alphaproteobacteria (5.6-6.7%). Despite exhibiting similar diversity indices and species richness, Betaproteobacteria (6.7%) and Gammaproteobacteria (11.1%) were solely present in E. foetida and P. excavatus, respectively. A set of 33 distinct morphotypes, including 18 from E. foetida and 15 from P. excavatus were selected. Carbohydrate utilization profiles generated using Hi-Carbo™ kits revealed that the isolates from the gut of P. excavatus - Arthrobacter pascens IARI-L13 and Bacillus subtilis IARIC were able to utilize 54 and 51.4% of the carbohydrates tested. Sorbose was not utilized, while unusual carbohydrates - adonitol and methyl-d-mannoside were utilized only by members from the gut of P. excavatus, while melizitose was utilized by those uniquely by E. foetida microbiome. Functional characterization revealed that ß-glucosidase activity was most prevalent in the culturable microbial community. Alkaline and acid phosphatase activity was more widespread in the E. foetida gut microbiome. All the culturable gut bacterial isolates produced ammonia, but IAA was detected only in five cultures. The unique functional attributes of the two culturable microbiomes, grown on a similar diet, reveals the significance of proper selection of earthworm substrate combinations for effective vermicomposting.

Deciphering the factors associated with the colonization of rice plants by cyanobacteria.

Cyanobacteria-rice plant interactions were analyzed using a hydroponics experiment. The activity of plant defense and pathogenesis-related enzymes, scanning electron microscopy, growth, nitrogen fixation (measured as ARA), and DNA fingerprinting assays proved useful in illustrating the nature of associations of cyanobacteria with rice plants. Microscopic analyses revealed the presence of short filaments and coiled masses of filaments of cyanobacteria near the epidermis and cortex of roots and shoot tissues. Among the six cyanobacterial strains employed, Calothrix sp. (RPC1), Anabaena laxa (RPAN8), and Anabaena azollae (C16) were the best performing strains, in terms of colonization in roots and stem. These strains also enhanced nitrogen fixation and stimulated the activity of plant defense/cell wall-degrading enzymes. A significantly high correlation was also recorded between the elicited plant enzymes, growth, and ARA. DNA fingerprinting using highly iterated palindromic sequences (HIP-TG) further helped in proving the establishment of inoculated organisms in the roots/shoots of rice plants. This study illustrated that the colonization of cyanobacteria in the plant tissues is facilitated by increased elicitation of plant enzymes, leading to improved plant growth, nutrient mobilization, and enhanced plant fitness. Such strains can be promising candidates for developing "cyanobacteria colonized-nitrogen-fixing rice plants" in the future.

Metabolite profiling of plant growth promoting cyanobacteria-Anabaena laxa and Calothrix elenkinii, using untargeted metabolomics.

The metabolite profiles of two plant growth promoting cyanobacteria-Anabaena laxa and Calothrix elenkinii, which serve as promising biofertilizers, and biocontrol agents were generated to investigate their agriculturally beneficial activities. Preliminary biochemical analyses, in terms of total chlorophyll, total proteins, and IAA were highest at 14 days after inoculation (DAI). In A. laxa 20-25% higher values of reducing sugars, than C. elenkinii at both 14 and 21 DAI were recorded. Carbon and nitrogen assimilating enzyme activities-phosphoenol pyruvate carboxylase (PEPC), carbonic anhydrase (CA), and glutamine synthetase (GS) were highest at 14 DAI, albeit, nitrate reductase (NR) activity was higher by 0.73-0.84-fold at 21 DAI. Untargeted GC-MS (Gas chromatography-Mass spectrometric) analysis of metabolite profiles of 21d-old cyanobacterial cultures and characterization using NIST mass spectral library illustrated that A. laxa recorded highest number of metabolite hits in three chemical classes namely amino acid and peptides, nucleotides, nucleosides and analogues, besides other organic compounds. Based on the pathway analysis of identified metabolites, both A. laxa, and C. elenkinii were enriched in metabolites involved in aminoacyl-tRNA biosynthesis, and amino acid metabolism pathways, particularly lactose and glutamic acid, which are important players in plant-microbe interactions. Correlation-based metabolite network illustrated distinct and significant differences in the metabolic machinery of A. laxa and C. elenkinii, highlighting their novel identity and enrichment in C-N rich metabolites, as factors underlying their plant growth and soil fertility enhancing attributes, which make them valuable as inoculants. Supplementary Information: The online version contains supplementary material available at 10.1007/s13205-023-03902-7.

Molecular characterization of a fungicidal endoglucanase from the cyanobacterium Calothrix elenkinii.

A gene responsible for fungicidal activity was identified in the cyanobacterial strain Calothrix elenkinii RPC1, which had shown promise as a biocontrol agent. Functional screening of the genomic library revealed fungicidal (against Pythium aphanidermatum) and endoglucanase activities in two clones. Sequencing revealed an open reading frame of 1,044 bp, encoding 348 amino acid residues with a predicted molecular weight of 38 kDa. Analysis of the deduced amino acid sequence of the putative gene (cael1) showed 99% similarity with the ß-1,4-endoglucanase from Anabaena laxa RPAN8 and 97% with the glucanase belonging to the peptidase M20 family of Anabaena variabilis and Nostoc sp. PCC7120, respectively. The putative promoters, ribosomal binding sites and a signal peptide of 22 amino acid residues were identified, revealing the secretory nature of the protein. The phylogenetic tree indicated a close relationship of the gene with Bacillus sp. This study is the first to report on the characterization of an endoglucanase in Calothrix sp.

Influence of phosphorus and pH on the fungicidal potential of Anabaena strains.

The genus Anabaena is known to be a rich source of bioactive metabolites, but the biocontrol potential of this genus, mediated through hydrolytic enzymes is less investigated. In our investigation, five Anabaena strains - A. laxa RPAN8, A. iyengarii RPAN9, A. variabilis RPAN59 and A. oscillarioides RPAN69 (with A. variabilis RPAN16 serving as negative control) were evaluated in time course studies involving incubation under three levels of phosphorus and pH conditions. Total chlorophyll, proteins, chitosanase, endoglucanase and CMCase activity were measured and inhibition assayed against phytopathogenic fungi. The four weeks old RPAN69 culture showed significantly higher chlorophyll which was 41% higher than control. This was also linked with an enhancement of 18.26% and 9.18% in chitosanase and CMCase activity respectively over control in the treatment involving half dose of phosphorus. Chlorophyll and CMCase activity showed a high degree of correlation with highest values at pH 9.5. A pH of 5.5 was the most suitable condition for the maximum activity of chitosanase for all the strains except RPAN16. The strains RPAN8 and RPAN9 showed the highest activity of endoglucanase at pH 5.5 while the other strains exhibited maximum activity at pH 7.5. This study provides insight into the role of P and pH in modulating fungicidal activity in different Anabaena strains, which can be valuable for enhancing their efficiency as a biocontrol agent.

Exploring nutritional modes of cultivation for enhancing lipid accumulation in microalgae.

The objective of this study was to identify the most promising nutritional mode of growth for enhanced biomass and lipid productivity in a set of twenty microalgal strains, grown under photoautotrophic and mixotrophic/heterotrophic conditions using 2% glucose as carbon source. These included four cyanobacterial strains (Cyanosarcina, Phormidium, Nostoc and Anabaena) and sixteen green algae belonging to six genera (five strains each of Chlorella and Chlorococcum, two of Scenedesmus and one each of Chlamydomonas, Kirchneria, Bracteacoccus and Ulothrix). Lipid productivity ranged from 2-13% under photoautotrophic conditions, 1.7-32% under mixotrophic conditions and 0.9-20% under heterotrophic conditions. MIC-G5 Chlorella sp. followed by MIC-G11 Chlorella sp. exhibited the highest cellular lipid content (355 and 271 µg/ml) and lipid productivity of 32% and 28% respectively in mixotrophic condition. In the glucose supplemented conditions (heterotrophic), a significant reduction in PUFA from 25.1 to 9.4, 29.2 to 12.4 and 44.7 to 10.2 was observed in MIC-G4, MIC-G5 and MIC-G11, respectively. A remarkable enhancement of 33-70% in SFA was recorded under mixotrophic conditions. As the quality of biodiesel is based on high SFA and low PUFA, our results illustrate the significance of glucose supplemented condition as a promising strategy for generating high value biodiesel from algae.

Physiological characterization and molecular profiling of toxic and non-toxic isolates of cyanobacterium Microcystis.

Our investigation aimed to utilize physiological attributes and molecular tools for distinguishing the toxic strain of Microcystis from other non toxic strains, belonging to the same genus. Physiological characterization of five Microcystis isolates indicated that the toxic strain (M1) exhibited significantly higher pigment accumulation (phycocyanin: 54.20 microg ml(-1); allophycocyanin: 18.2 microg ml(-1)) and sugar content (74.25 microg ml(-1)), which may be providing a competitive advantage for successful colonization and proliferation. Profiling using repeat sequence primers (STRR, Hip) was helpful in distinguishing different strains (M1-M5) and HIP TG profile was unique to M1. SDS-PAGE profile of the five strains indicated the presence of a unique band (25kDa) in M1. The combined use of SDS-PAGE and HipTG profiles can help in providing distinct fingerprint for the toxic strain, which can be useful in its identification.