B. Anandkumar

Characterization of corrosive bacterial consortia isolated from petroleum-product-transporting pipelines

Microbiologically influenced corrosion is a problem commonly encountered in facilities in the oil and gas industries. The present study describes bacterial enumeration and identification in diesel and naphtha pipelines located in the northwest and southwest region in India, using traditional cultivation technique and 16S rDNA gene sequencing. Phylogenetic analysis of 16S rRNA sequences of the isolates was carried out, and the samples obtained from the diesel and naphtha-transporting pipelines showed the occurrence of 11 bacterial species namely Serratia marcescens ACE2, Bacillus subtilis AR12, Bacillus cereus ACE4, Pseudomonas aeruginosa AI1, Klebsiella oxytoca ACP, Pseudomonas stutzeri AP2, Bacillus litoralis AN1, Bacillus sp., Bacillus pumilus AR2, Bacillus carboniphilus AR3, and Bacillus megaterium AR4. Sulfate-reducing bacteria were not detected in samples from both pipelines. The dominant bacterial species identified in the petroleum pipeline samples were B. cereus and S. marcescens in the diesel and naphtha pipelines, respectively. Therefore, several types of bacteria may be involved in biocorrosion arising from natural biofilms that develop in industrial facilities. In addition, localized (pitting) corrosion of the pipeline steel in the presence of the consortia was observed by scanning electron microscopy analysis. The potential role of each species in biofilm formation and steel corrosion is discussed.

Studies to control biofilm formation by coupling ultrasonication of natural waters and anodization of titanium

The main objective of this study was to investigate the combined effect of ultrasonication of natural waters and anodization of titanium on microbial density and biofilm formation tendency on titanium surfaces. Application of 24 kHz, 400 W high power ultrasound through a 14 mm horn type SS (stainless steel) Sonicator with medium amplitude of 60% for 30 min brought about three order decrease in total bacterial density of laboratory tap water, cooling tower water and reservoir water and two order decrease in seawater. Studies on the effect of ultrasonication on dilute pure cultures of Gram-negative and Gram-positive bacteria showed five order and three order decrease for Pseudomonas sp. and Flavobacterium sp. respectively and two order and less than one order decrease for Bacillus sp. and Micrococcus sp. respectively. Ultrasonication increased lag phase and reduced logarithmic population increase and specific growth rate of Gram-negative bacteria whereas for Gram-positive bacteria specific growth rate increased. Studies on the biofilm formation tendency of these ultrasonicated mediums on titanium surface showed one order reduction under all conditions. Detailed biofilm imaging by advanced microscopic techniques like AFM, SEM and epifluorescence microscopy clearly visualized the lysed/damaged cells and membrane perforations due to ultrasonication. Combination of ultrasonication and anodization brought about maximum decrease in bacterial density and biofilm formation with greater than two order decrease in seawater, two order decrease in Bacillus sp. culture and more than four order decrease in Flavobacterium sp. culture establishing the synergistic effect of anodization and ultrasonication in this study.

A silver nanoparticle loaded TiO2 nanoporous layer for visible light induced antimicrobial applications.

A nanoporous TiO2 layer was formed on commercially pure titanium by a simple anodization method in aqueous hydrofluoric acid (HF) medium. Silver nanoparticles (AgNP) were loaded into the nanoporous TiO2 layer by UV light irradiation. The morphology, chemical composition and photocatalytic activity of the modified titanium surfaces were characterized by scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and UV-vis absorption spectroscopy techniques. The redox behavior of the AgNP loaded TiO2 layer was analyzed by cyclic voltammetry (CV) studies. The impedance behavior of the nanoporous TiO2 layer with and without AgNP was investigated by electrochemical impedance spectroscopy (EIS). The antibacterial effect of the AgNP loaded TiO2 layer was evaluated using Pseudomonas sp. and Bacillus sp. cultures. The efficacy of this modified layer to act as an antibacterial agent to minimize biofouling of titanium is demonstrated in this investigation.

Studies of detailed Biofilm characterization on fly ash concrete in comparison with normal and superplasticizer concrete in seawater environments

In cooling water systems, many concrete structures in the form of tanks, pillars and reservoirs that come in contact with aggressive seawater are being deteriorated by chemical and biological factors. The nuclear industry has decided to partially replace the Portland cement with appropriate pozzolans such as fly ash, which could densify the matrix and make the concrete impermeable. Three types of concrete mixes, viz., normal concrete (NC), concrete with fly ash and superplasticizer (FA) and concrete with only superplasticizer (SP) were fabricated for short- and long-term exposure studies and for screening out the better concrete in seawater environments. Biofilm characterization studies and microscopic studies showed excellent performance of FA concrete compared to the other two. Laboratory exposure studies in pure cultures of Thiobacillus thiooxidans and Fusarium oxysporum were demonstrated for the inhibition of microbial growth on fly ash. Epifluorescence and scanning electron microscopic studies supported the better performance of the FA specimen. Thus, the present study clearly showed that FA concrete is less prone to biofilm formation and biodeterioration.

Reduced graphene oxide/nano-Bioglass composites: processing and super-anion oxide evaluation

45S5 Bioglass with a mean particle size in the nano regime were synthesized and fabricated with rGO sheets using three different strategies. The fabricated nanocomposites were analysed for their bond formation and defects. Morphology, size and distribution of n-BG particles on rGO were visualised. An attempt to understand the superoxide anion production by n-BG particles, rGO and its nanocomposites was made.

Studies on microbiologically influenced corrosion of SS304 by a novel manganese oxidizer, Bacillus flexus

A manganese oxidizing bacterium was isolated from the surface of steel scraps and biochemical tests and 16S rRNA sequencing analysis confirmed the isolate as Bacillus flexus. Potentiodynamic polarization curves showed ennoblement of open circuit potential, increased passive current, a lowering of breakdown potential, active re-passivation potential and enhanced cathodic current in the presence of B. flexus. Adhesion studies with B. flexus on SS304 specimens with different surface treatments demonstrated decreased adhesion on passivated and FeCl3 treated specimens due to the removal of MnS inclusions. The present study provides evidence that surface treatment of stainless steels can reduce adhesion of this manganese oxidizing bacterium and decrease the probability of microbiologically influenced corrosion.

Corrosion characteristics of sulfate-reducing bacteria (SRB) and the role of molecular biology in SRB studies: an overview

Abstract Sulfate-reducing bacteria (SRB), an anaerobic bacterial group, are found in many environments like freshwater, marine sediments, agricultural soil, and oil wells where sulfate is present. SRB derives energy from electron donors such as sulfate, elemental sulfur or metals, and fermenting nitrate. It is the major bacterial group involved in the microbiologically influenced corrosion (MIC), souring, and biofouling problems in oil-gas-producing facilities as well as transporting and storage facilities. SRB utilizes sulfate ions as an electron acceptor and produce H2S, which is an agent of corrosion, causing severe economic damages. Various theories have been proposed on the direct involvement of H2S and iron sulfides in corrosion; H2S directly attacks and causes corrosion of metals and alloys. Many reviews have been presented on the aforementioned aspects. This review specifically focused on SRB corrosion and the role of molecular biology tools in SRB corrosion studies viz. cathodic and anodic depolarization theories, corrosion characteristics of thermophilic SRB and influence of hydrogenase, temperature, and pressure in thermophilic SRB corrosion, SRB taxonomy, molecular approaches adopted in SRB taxonomical studies, sulfate and citrate metabolism analyses in completed SRB genomes, and comparative studies on SRB’s dissimilatory sulfite reductase structures.

Decoration of 1-D nano bioactive glass on reduced graphene oxide sheets: Strategies and in vitro bioactivity studies

45S5 Bioglass® is the most widely studied class of bioceramic in the field of dental and orthopedics. The present study highlights, one-dimensional bioactive glass nanorods (BGNR) of 45S5 composition synthesized by tuning the parameters of sol-gel process and hybridized with two-dimensional reduced graphene oxide sheets (rGO). BGNR was integrated with rGO by three different methods to form nano hybrids of rGO/BGNR. The prepared BGNR revealed combeite high mineral phase (Na5.27Ca3Si6O18) whereas nano hybrids exhibited calcite mineral phase (CaCO3) along with combeite in XRD analysis. The morphology, size of BGNR and integration of BGNR with rGO were analyzed using SEM. Nano hybrids were subjected to biological characterizations to identify the bio-activity (mineralization), antibacterial efficacy, hemocompatibility and cell proliferation efficacies. These studies conclude that the one-dimensional BGNR, micron-sized reduced graphene oxide sheet and the calcite phase in nano hybrids play a crucial role in enhancing the bioactivity, antibacterial activity, hemocompatibility and cell proliferation. These findings suggest the synergistic effect of rGO/BGNR nano hybrids will open new venue for biomaterials in the field of implant materials.