Shivanthi Anandan

Rapid Inactivation of Airborne Bacteria Using Atmospheric Pressure Dielectric Barrier Grating Discharge

Dielectric barrier discharge plasma has been known to inactivate many different microorganisms on surfaces when treatment times are on the order of seconds or minutes in duration. In this paper, a unique plasma air cleaning facility was created which combines a dielectric barrier grating discharge (DBGD) with a filterless laboratory-scale ventilation system and is used to treat concentrated bacterial bioaerosol in a moving air stream at air flow rates of 25 L/s. Results indicate that plasma treatment times on the order of milliseconds corresponding to one pass through the DBGD device can achieve 1.5-log reduction in culturable E. coli immediately after contact with plasma and 5-log reduction totally following in the minutes after the plasma treatment. A numerical characterization study was performed to help predict and understand the mechanism of bacteria inactivation in the DBD plasma from a variety of plasma factors.

Decontamination of Surfaces From Extremophile Organisms Using Nonthermal Atmospheric-Pressure Plasmas

We showed that nonthermal dielectric barrier discharge (DBD) plasma compromises the integrity of the cell membrane of Deinococcus radiodurans, an extremophile organism. In samples of D. radiodurans, which were dried in a laminar flow hood, we observe that DBD plasma exposure resulted in a six-log reduction in CFU (colony-forming unit) count after 30 min of treatment. When the Deinococcus radiodurans cells were suspended in distilled water and treated, it took only 15 s to achieve a four-log reduction of CFU count.

Inactivation of Bacteria in Flight by Direct Exposure to Nonthermal Plasma

Plasma treatment is a promising technology for fast and effective sterilization of surfaces, waterflow, and airflow. The treatment of airflow is an important area of healthcare and biodefense that has recently gained the interest of many scientists. In this paper, we describe a dielectric barrier grating discharge (DBGD) which is used to study the inactivation of airborne Escherichia coli inside a closed air circulation system. Earlier published results indicate approximately 5-log reduction (99.999%) in the concentration of the airborne bacteria after single DBGD exposure of 10-s duration. This paper investigates plasma species influencing the inactivation. The two major factors that are studied are the effect of charged and short-lived species (direct exposure to plasma) and the effect of ozone. It is shown that for a 25% reduction in direct exposure, the inactivation falls from 97% to 29% in a single pass through the grating. The influence of ozone was studied by producing ozone remotely with an ozone generator and injecting the same concentration into the system, as that produced by the DBGD plasma. The results show a 10% reduction in the bacterial load after 10-s exposure to ozone; thus, ozone alone may not be one of the major inactivating factors in the plasma.

Microbial Quality of Food Available to Populations of Differing Socioeconomic Status

BACKGROUND Low SES has been shown to be linked to poorer-quality diets, decreased consumption of fresh produce, and an increased reliance on small retail stores. PURPOSE The objective of this research was to determine if there is a difference in the microbial quality and potential safety of food available to low-SES versus high-SES populations at the retail level. METHODS Aerobic plate count (APC); yeast and mold counts (Y & M); and total coliforms were determined in ready-to-eat (RTE) greens, pre-cut watermelon, broccoli, strawberries, cucumbers, milk, and orange juice and compared among products purchased in stores in low- versus those purchased in high-SES neighborhoods between June 2005 and September 2006. APC, fecal coliforms, and E. coli in ground beef and the presence of Salmonella and Campylobacter in chicken were also compared. RESULTS Results showed higher microbial loads on produce from markets in low-SES areas. Significant differences observed included (1) APC and Y&M in RTE greens, (2) APC and Y&M in strawberries, and (3) YMCs in cucumbers. No difference was detected in the level of pathogens in raw meat and poultry; however, the APC in ground beef available in high-SES markets was significantly higher compared with that found in low-SES markets. CONCLUSIONS The results presented here indicate that populations of low SES may be more likely to experience produce of poorer microbial quality, which may have an impact on both the appeal and potential safety of the produce.

Indoor-Biofilter Growth and Exposure to Airborne Chemicals Drive Similar Changes in Plant Root Bacterial Communities

ABSTRACT Due to the long durations spent inside by many humans, indoor air quality has become a growing concern. Biofiltration has emerged as a potential mechanism to clean indoor air of harmful volatile organic compounds (VOCs), which are typically found at concentrations higher indoors than outdoors. Root-associated microbes are thought to drive the functioning of plant-based biofilters, or biowalls, converting VOCs into biomass, energy, and carbon dioxide, but little is known about the root microbial communities of such artificially grown plants, how or whether they differ from those of plants grown in soil, and whether any changes in composition are driven by VOCs. In this study, we investigated how bacterial communities on biofilter plant roots change over time and in response to VOC exposure. Through 16S rRNA amplicon sequencing, we compared root bacterial communities from soil-grown plants with those from two biowalls, while also comparing communities from roots exposed to clean versus VOC-laden air in a laboratory biofiltration system. The results showed differences in bacterial communities between soil-grown and biowall-grown plants and between bacterial communities from plant roots exposed to clean air and those from VOC-exposed plant roots. Both biowall-grown and VOC-exposed roots harbored enriched levels of bacteria from the genus Hyphomicrobium. Given their known capacities to break down aromatic and halogenated compounds, we hypothesize that these bacteria are important VOC degraders. While different strains of Hyphomicrobium proliferated in the two studied biowalls and our lab experiment, strains were shared across plant species, suggesting that a wide range of ornamental houseplants harbor similar microbes of potential use in living biofilters.

General effect of photosynthetic electron transport inhibitors on translation precludes their use for investigating regulation of D1 biosynthesis in Synechococcus sp. strain PCC 7942

Both light itself and excitation pressure have been implicated as the environmental signal that stimulates interchange of the two forms of the D1 protein of photosystem II (PS II) in Synechococcus sp. strain PCC 7942. We sought an explanation for conflicting reports regarding the role of photosynthetic electron transport in regulation of psbA expression and D1 interchange. Inhibitors that block at different points in the photosynthetic electron transport chain were administered and the effect on expression of psbAII, which encodes the high-light-induced form II of D1, was examined by measuring changes in transcript levels and in the activities of reporter enzymes. Both 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), an inhibitor of PSII, and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB), an inhibitor of the cytochrome b6/f complex, prevented high-light-induced increase in β-galactosidase activity from a psbAII::lacZ gene fusion when added at a concentration that completely inhibits photosynthetic electron transport (1 μM). The same effect was observed for luciferase activity from transcriptional and translational fusions of psbAII to the luxAB genes from Vibrio harveyi. DCMU (1 μM) arrested luciferase expression at low-light levels – thus eliminating the high light response – whereas a sublethal concentration (50 nM), which reduces electron transport by 50%, had intermediate effects on psbAII-driven luciferase activity. However, psbAII transcript levels, monitored by northern blot analysis, were not altered by electron transport inhibitors, either at low-light intensity or following a high-light exposure. The suppressive effect of DCMU on expression of reporter enzymes was not restricted to the high-light response of psbAII-driven reporter systems, but was also observed using an isopropyl-(-d)-thiogalactopyranoside (IPTG)-inducible trc promoter fused to luxAB. This construct only marginally responded to IPTG addition when DCMU was present. Thus, blocking electron transport in Synechococcus affects the translation machinery in a general way, and the use of electron transport inhibitors is of limited value when focusing on specific redox regulation of D1 protein synthesis or degradation.

DNA microarrays detect effects of soil contamination on Arabidopsis thaliana gene expression

Soil contamination, such as heavy metals and benzene compounds, is a widespread problem on military installations. It is important to be able to determine the effects of soil contamination before any adverse effects appear in organisms in surrounding areas. We examined gene expression in Arabidopsis thaliana grown in soil from three sites at the Radford Army Ammunition Plant in Radford, Virginia, USA, using DNA microarrays. We analyzed soil, germination, and growth rate to compare with the microarray data. Soil contamination affected both external phenotype and gene expression. Plants grown in soil with high levels of contaminants were chloritic and were smaller than control plants grown in potting soil. Plants grown in soil with the highest copper concentration had the lowest growth rates and had genes up-regulated across several functional groups. Plants grown in soils with elevated lead had many genes down-regulated that were related to photosystem II, metabolism, cellular transport, and protein synthesis. Genes consistently up-regulated across most microarrays were genes related to photosystem I, genes related to water deprivation and oxidative stress response, heat shock proteins, and toxin catabolism genes such as glutathiones. DNA microarrays, in concert with a model genetic organism such as A. thaliana, were an effective assessment tool to determine the presence of toxic substances in soil at a site used for the production of military explosives.

Identification of two classes of transcriptional regulator genes in the cyanobacterium Synechococcus sp. strain PCC 7942

Abstract We designed a strategy to isolate and characterize response regulator genes from the cyanobacterium Synechococcus sp. strain PCC 7942 based on the premise that cyanobacterial response regulators would bear strong similarity to their counterparts from other eubacteria. Two response regulator genes, srrA and srrB, were isolated from Synechococcus and found to encode proteins similar to the OmpR subclass of response regulators. Disruption of either gene by insertional mutagenesis did not produce an obvious phenotype and did not affect the accumulation of psbAII mRNA under high-light conditions, indicating that these gene products are not involved in mediating the well characterized standard- to high-light transition response of photosystem II genes in this cyanobacterium. Analysis of the chromosomal region adjacent to srrA revealed the presence of another presumptive transcriptional activator gene. This gene, named lrrA, belongs to the lysR family. Attempts to disrupt lrrA or an adjacent ORF (orfG) were not successful, suggesting that these genes are important for the growth of Synechococcus.

Air and Water Sterilization using Non-Thermal Plasma

The sterilization effect of plasma on air and water were investigated in this study*. For air sterilization, a small scale model of HVAC was designed and Dielectric Barrier Discharge plasma source was used for treatment of air. This PDRF (Pathogen Detection and Remediation Facility) consisted of a circulatory airflow system, a plasma chamber and a sampling system. Air sterilization experiments were performed and the inactivation of Escherichia coli was studied. Conventional water sterilization methods such as chlorination, ozonation, filtration, UV irradiation etc have several drawbacks. Pulsed plasma discharge for the destruction of microorganisms in waste water and potable water is a cost effective technique developed recently. The energy efficiency of different types of plasma discharges in water contaminated with Escherichia coli has been studied. The effect of initial concentration of bacterial solution on the inactivation efficiency has also been studied

The TrpA protein of Trichodesmium erythraeum IMS101 is a non-fibril-forming collagen and a component of the outer sheath.

Collagen molecules are structural in nature and primarily found in eukaryotic, multicellular organisms. Recently, a collagen-like protein, TrpA, was identified and characterized in the marine cyanobacterium Trichodesmium erythraeum IMS 101, and it was shown to be involved in maintaining the structural integrity of the trichomes. The TrpA protein contains one glycine interruption in the otherwise perfectly uninterrupted collagenous domain. In this study, we used phylogenetic analysis to determine that the TrpA protein sequence is most closely associated with non-fibril-forming collagen proteins. Structural modelling and circular dichroism data suggest that the glycine insertion decreases the stability of TrpA compared to uninterrupted collagen sequences. Additionally, scanning electron microscopy revealed that TrpA is expressed entirely on the surface of the trichomes, with no specific pattern of localization. These data indicate that the TrpA protein is part of the outer sheath of this organism. As such, this protein may function to promote adhesion between individual T. erythraeum trichomes, and between this organism and heterotrophic bacteria found in the same environment.