Impairment of ntcA gene revealed its role in regulating iron homeostasis, ROS production and cellular phenotype under iron deficiency in cyanobacterium Anabaena sp. PCC 7120.

Iron deficiency ends up into several unavoidable consequences including damaging oxidative stress in cyanobacteria. NtcA is a global nitrogen regulator controls wide range of metabolisms in addition to regulation of nitrogen metabolism. In present communication, NtcA based regulation of iron homeostasis, ROS production and cellular phenotype under iron deficiency in Anabaena 7120 has been investigated. NtcA regulates the concentration dependent iron uptake by controlling the expression of furA gene. NtcA also regulated pigment synthesis and phenotypic alterations in Anabaena 7120. A significant increase in ROS production and corresponding reduction in the activities of antioxidative enzymes (SOD, CAT, APX and GR) in CSE2 mutant strain in contrast to wild type Anabaena 7120 also suggested the possible involvement of NtcA in protection against oxidative stress in iron deficiency. NtcA has no impact on the expression of furB and furC in spite of presence of consensus NtcA binding site (NBS) and -10 boxes in their promoter. NtcA also regulates the thylakoid arrangement as well as related photosynthetic and respiration rates under iron deficiency in Anabaena 7120. Overall results suggested that NtcA regulates iron acquisition and in turn protect Anabaena cells from the damaging effects of oxidative stress induced under iron deficiency.

Molecular phylogeny of heterotrophic nitrifiers and aerobic denitrifiers and their potential role in ammonium removal.

To investigate the physiology and taxonomic composition of the key players of nitrification and denitrification processes in paddy fields, culture dependent and independent studies have been carried out. A total of 28 bacterial strains have been screened in which six were capable of reducing nitrate and nitrite as well as having significant ammonium removal potential. 16S rRNA-PCR-DGGE-based molecular typing of enriched batch culture was done with time duration to explore and identify dominant and stable soil denitrifiers. Notably, three isolates namely PDN3, PDN19, PDN14 were found to be efficiently involved in the removal of 70.32, 71.46, and 81.50% of NH4 (+) and showed closest similarity (>98%) with Bacillus cereus, Bacillus subtilis, and Pseudomonas aeruginosa strains, respectively. The bacterial strain PDN14 showed maximum growth with highest ammonium removal rate (2.78 gN/(m(3) ·h) has also been characterized based on nosZ gene which showed similarity to uncultured γ- Proteobacteria, P. aeruginosa sp. B3. Median joining (MJ) network and rRNA secondary structure have been analyzed for their detailed taxonomic diversity and derived haplotype-based co-occurrence. Results demonstrated that such strains can serve as good candidate for in situ nitrogen transformation in paddy soils and improvingly characterized by physiological and detailed phylogenetic approaches.

Role of manganese in protection against oxidative stress under iron starvation in cyanobacterium Anabaena 7120.

The cyanobacterium Anabaena sp. PCC 7120 was grown in presence and absence of iron to decipher the role of manganese in protection against the oxidative stress under iron starvation and growth, manganese uptake kinetics, antioxidative enzymes, lipid peroxidation, electrolyte leakage, thiol content, total peroxide, proline and NADH content was investigated. Manganese supported the growth of cyanobacterium Anabaena 7120 under iron deprived conditions where maximum uptake rate of manganese was observed with lower K(m) and higher V(max) values. Antioxidative enzymes were also found to be elevated in iron-starved conditions. Estimation of lipid peroxidation and electrolyte leakage depicted the role of manganese in stabilizing the integrity of the membrane which was considered as the prime target of oxygen free radicals in oxidative stress. The levels of total peroxide, thiol, proline and NADH content, which are the representative of oxidative stress response in Anabaena 7120, were also showed increasing trends in iron starvation. Hence, the results discerned, clearly suggested the role of manganese in protection against the oxidative stress in cyanobacterium Anabaena 7120 under iron starvation either due to its antioxidative properties or involvement as cofactor in a number of antioxidative enzymes.

Phylogenetic analysis of heterocystous cyanobacteria (Subsections IV and V) using highly iterated palindromes as molecular markers.

Highly iterated palindromes (HIP) have been used as high resolution molecular markers for assessing the genetic variability and phylogenetic relatedness of heterocystous cyanobacteria (subsections IV and V) representing 12 genera of heterocystous cyanobacteria, collected from different geographical areas of India. DNA fingerprints generated using four HIP markers viz. HIP-AT, HIP-CA, HIP-GC, and HIP-TG showed 100 % polymorphism in all the heterocystous cyanobacteria studied and each marker produced unique and strain-specific banding pattern. Furthermore, phylogenetic affinities based on the dendrogram constructed using HIP DNA profiles of heterocystous cyanobacteria suggest the monophyletic origin of this entire heterocystous clade along with a clear illustration of the polyphyletic origin of the branched Stigonematalean order (Subsection V). In addition, phylogenetic affinities were validated by principal component analysis of the HIP fingerprints. The overall data obtained by both the phylogeny and principal component assessments proved that the entire heterocystous clade was intermixed, and there are immediate needs for classificatory reforms that satisfy morphological plasticity and environmental concerns.

Comparative responses of diazotrophic abundance and community structure to the chemical composition of paddy soil.

Diazotrophy is considered as one of the most crucial and dynamic phenomena in the rice field and also a major source of nitrogen input. The objective of this study was to elucidate possible interactions between diverse and dominant diazotrophic bacterial community and organic carbon composition of the paddy soil. Our results suggest that most abundantly found diazotrophs belong to a proteobacteria group and uncultured bacterial forms. A gene abundance study clearly showed significantly higher diazotrophic abundance (P < 0.01) at Chandauli (CHN) as compared to Varanasi (VNS) and Ghazipur (GHJ) districts of Eastern Uttar Pradesh, India, with nitrogenase reductase (nifH) copy number between 1.44 × 103 and 3.34 × 103 copy g-1 soil. Fourier-transform infrared (FT-IR) spectroscopy data identified -CO-, C=O ([Formula: see text] and -NH-), [Formula: see text], and OH- as dominant organic functional groups in the paddy soil. Multivariate analysis was performed to get a clear and more accurate picture of interactions between free-living diazotrophs and abiotic soil factors. Regression analysis suggested a similar trend of distribution of different functional groups along each site. Relative abundance and diversity of diazotrophic population increased in response to FT-IR-based soil organic fractions. Maximum number of FT-IR spectral peak at sites in the Chandauli district augmented its bacterial diazotrophic diversity and abundance. Taken together, the present study sheds light on the substrate-driven composition of the microbial population of selected paddy areas.

Nitric oxide ameliorates the damaging effects of oxidative stress induced by iron deficiency in cyanobacterium Anabaena 7120.

In cyanobacterium Anabaena 7120, iron deficiency leads to oxidative stress with unavoidable consequences. Nitric oxide reduces pigment damage and supported the growth of Anabaena 7120 in iron-deficient conditions. Elevation in nitric oxide accumulation and reduced superoxide radical production justified the role of nitric oxide in alleviating oxidative stress in iron deficiency. Increased activities of antioxidative enzymes and higher levels of ROS scavengers (ascorbate, glutathione and thiol) in iron deficiency were also observed in the presence of nitric oxide. Nitric oxide also supported the membrane integrity of Anabaena cells and reduces protein and DNA damage caused by oxidative stress induced by iron deficiency. Results suggested that nitric oxide alleviates the damaging effects of oxidative stress induced by iron deficiency in cyanobacterium Anabaena 7120.

Deciphering the evolutionary affiliations among bacterial strains (Pseudomonas and Frankia sp.) inhabiting same ecological niche using virtual RFLP and simulation-based approaches.

To decipher an evolutionary lineage between two different but important bacterial groups, i.e., Pseudomonas strain (γ-Proteobacteria) and Frankia strain (actinobacteria) growing in the same ecological niche in and around of an actinorhizal plant Hippophae salicifolia D. Don, genetic diversity and comparative molecular phylogeny have been investigated using 16S rRNA gene sequences and computer-simulated and virtually directed restriction fragment length polymorphism (RFLP) through 10 restriction enzymes. Bayesian and coalescent analyses on the basis of 16S rRNA gene sequences suggested three major groups with close proximity between Pseudomonas and Frankia isolates. This result has been further validated based on the data observed through similarity coefficient value and computational RFLP. Principal component analysis and Mandel h and k statistical analysis also confirmed and strengthen the findings. Approximately 458 aligned sequence of all the taxa were used to decipher nucleotide diversity, polymorphism and gene flow between these taxa. Thus, our results suggest for a possible co-evolution or a heterologous gene transfer of distantly related microbial forms. Further, our study also advocate for the use of computer aided, virtual RFLP analysis as a cost effective and rapid identification tool.