Krishnaswamy Jayachandran

Kinetics of chromium (VI) reduction by a type strain Shewanella alga under different growth conditions.

We conducted kinetic batch experiments to determine the reduction of Chromium(VI) by a type strain of Shewanella alga (BrY-MT) ATCC 55627. Chromium(VI) was reduced to Chromium(III) by BrY-MT grown in three different substrates: BHIB (brain heart infusion broth), TSB (tryptic soy broth), and M9 (minimum broth). Four different Cr(VI) concentrations 4.836, 10.00, 37.125, and 260.00 mg l-1 were reduced at different rates by BrY-MT in both aerobic and anaerobic conditions. BrY-MT grown in BHIB reduced the maximum amount of Cr(VI) followed by TSB and M9. Carbondioxide produced from bacterial respiration varied with and without Cr(VI) under both aerobic and anaerobic conditions. The Cr(VI) reduction data under anaerobic condition was fitted by a monod model to determine the bacterial kinetic parameters. The kinetic parameters determined by fitting the anaerobic experimental data were used to run a forward simulation for experiments conducted under aerobic conditions. The monod model was modified to account for an inhibition parameter for the Cr(VI) experiment at 260 mg l-1. All the parameters varied within a narrow range, and were distinct for different substrates. Our studies show that, successful in situ bioremediation of Cr(VI) is depended on the type of substrates (electron donors) and the concentration of Cr(VI) in geologic medium.

Chromium transport, oxidation, and adsorption in manganese-coated sand.

We examine how the processes of advection, dispersion, oxidation-reduction, and adsorption combine to affect the transport of chromium through columns packed with pyrolusite (beta-MnO2)-coated sand. We find that beta-MnO2 effectively oxidizes Cr(III) to Cr(VI) and that the extent of oxidation is sensitive to changes in pH, pore water velocity, and influent concentrations of Cr(III). Cr(III) oxidation rates, although initially high, decline well before the supply of beta-MnO2 is depleted, suggesting that a reaction product inhibits the conversion of Cr(III) to Cr(VI). Rate-limited reactions govern the weak adsorption of each chromium species, with Cr(III) adsorption varying directly with pH and Cr(VI) adsorption varying inversely with pH. The breakthrough data on chromium transport can be matched closely by calculations of a simple model that accounts for (1) advective-dispersive transport of Cr(III), Cr(VI), and dissolved oxygen, (2) first-order kinetics adsorption of the reduced and oxidized chromium species, and (3) nonlinear rate-limited oxidation of Cr(III) to Cr(VI). Our work supplements the limited database on the transport of redox-sensitive metals in porous media and provides a means for quantifying the coupled processes that contribute to this transport.

Microbiological reduction of chromium(VI) in presence of pyrolusite-coated sand by Shewanella alga Simidu ATCC 55627 in laboratory column experiments

Hexavalent chromium (Cr(VI)) was reduced to non-toxic trivalent chromium (Cr(III)) by a dissimilatory metal reducing bacteria, Shewanella alga Simidu (BrY-MT) ATCC 55627. A series of dynamic column experiments were conducted to provide an understanding of Cr(VI) reduction by the facultative anaerobe BrY-MT in the presence of pyrolusite (beta-MnO(2)) coated sand and uncoated-quartz sand. All dynamic column experiments were conducted under growth conditions using Cr(VI) as the terminal electron acceptor and lactate as the electron donor and energy source. Reduction of Cr(VI) was rapid (within 8 h) in columns packed with uncoated quartz sand and BrY-MT, whereas Cr(VI) reduction by BrY-MT was delayed (57 h) in the presence of beta-MnO(2)-coated sand. The role of beta-MnO(2) in this study was to provide oxidation of trivalent chromium (Cr(III)). BrY-MT attachment was higher on beta-MnO(2)-coated sand than on uncoated quartz sand at 10, 60, and 85.5 h. Results have shown that this particular strain of Shewanella did not appreciably reduce Mn(IV) to Mn(II) species nor biosorbed Cr and Mn during its metabolic activities.

Root structure and arbuscular mycorrhizal colonization of the palm Serenoa repens under field conditions

Serenoa repens (Bartr.) Small is a palm native to the southeastern USA. It is a common understory plant in pine communities on both acid sands and alkaline limestone. Roots have only primary growth and range in thickness from 8.0 mm (first order roots from the stem) to 0.8–2.9 mm (ultimate roots of third to fifth order). The thickest roots occur at soil depths >20 cm; fine roots (<1.2 mm) occur at all depths (1–60 cm). Some second and third order roots are negatively geotropic and grow up to the mineral soil surface. The epidermis of all roots has a thick, eventually lignified outer wall. Except for the thinnest, all roots have a single-layered, thick-walled exodermis, which is first suberized and later lignified. Root hairs are never present. A hypodermis composed of several layers of lignified cells (up to 8-cells-thick) is next to the exodermis and forms the outer cortex. Radial series of thin walled and slightly lignified cells sporadically occur in the outer cortex of the thinnest roots, but there are no passage cells in the exodermis, which is continuous. The remaining inner cortex is composed of unlignified parenchyma with air canals and a completely lignosuberized endodermis in old roots. Passage cells were seen the the endodermis of the some of the thinnest roots. Arbuscular mycorrhizal (AM) fungi occur in the outer one-third of the cortical parenchyma adjacent to the hypodermis. Fungal coils, arbuscules and vesicles are found most frequently in the thinnest roots, but also occur sporadically in all root orders. Cells a few mm from the apical meristem are sometimes colonized. At sites of appressoria, coils of AM hyphae occur within an epidermal cell and exodermal and hypodermal cells beneath. Intercellular hyphae with intracellular branch arbuscules (Arum-type) are common in the inner cortex. There is evidence of a dieback of the highest order roots during the winter dry season. Profiles of soil and roots have the highest density of AM spores in the surface 10 cm layer. Total AM spore density ranged from 130 to 1100 spores per 50 g soil in different samples. Glomus spp. dominated followed by Gigaspora spp. The findings are related to a more general understanding of growth and AM colonization in long-lived roots of tropical woody monocotyledons. Palm roots, in particular, are slow growing and are protected by massive hypodermal layers.

ARBUSCULAR MYCORRHIZAL FUNGI ENHANCE SEEDLING GROWTH IN TWO ENDANGERED PLANT SPECIES FROM SOUTH FLORIDA

Arbuscular mycorrhizal fungi (AMF) are reported and described in the fine roots of two federally listed endangered plant species: Amorpha crenulata Rydb. (Fabaceae) (crenulate lead plant or lusterspike indigobush) and Jacquemontia reclinata House ex Small (Convolvulaceae) (beach jacquemontia or beach clustervine). Wild‐grown plants have typical Arum‐type arbuscular mycorrhizae. Seedlings of these species were grown in pots with various native soil treatments under greenhouse conditions. Native mixed AMF from soil and roots growing in the natural communities pine rockland and beach back dune, respectively, were multiplied on Sudan grass and pigeon pea nurse cultures. Native sandy soil is low in available phosphorus (P), ranging from 8–18 ppm at the surface 0–5 cm to 2 ppm at 70 cm. AMF significantly increased the dry weight and total P content of seedlings growing on native soil. Additions of phosphate but without AMF also promoted seedling growth. Soil microbe filtrate had no effect on J. reclinata but did increase growth of A. crenulata, possibly by increased potential for Rhizobium inoculum for nitrogen‐fixing nodules in this legume.

Presence of arbuscular mycorrhizal fungi in South Florida native plants.

The roots of 27 species of South Florida plants in 15 families (including one cycad, six palms, one Smilax, and 19 dicotyledons) native to pine rockland and tropical hardwood hammock communities were examined for arbuscular mycorrhizal fungi (AMF). These plants grow in the biologically diverse but endangered Greater Everglades habitat. Roots from field-grown and potted plants were cleared and stained. All 27 species had AMF and include 14 species having an endangered or threatened status. The Paris-type colonization occurred in two species in the families Annonaceae and Smilacaceae. The Arum-type occurred in 22 species in the families Anacardiaceae, Arecaceae (Palmae), Boraginaceae, Cactaceae (questionable), Euphorbiaceae, Fabaceae, Lauraceae, Melastomataceae, Polygalaceae, Rubiaceae, Simaroubaceae, Ulmaceae, and Zamiaceae. Three species in the families Fabaceae, Lauraceae, and Simaroubaceae had a mix of Paris- and Arum-types. The results have implications for the restoration of these endangered plant communities in the Everglades.

An assessment of biodiesel feedstock conversion efficiency: a case study of decentralised biofuel production program in rural India

In response to a national ambitious biofuel policy, the Indian state of Karnataka launched a feedstock development program on the principles of decentralisation, sustainability, and multiple fuel sources. A network of farmers oilseed associations are being formed in order to encourage farmers to grow, pool and process a large number of small-scale oilseed productions. Success of such program depends on the conversion efficiencies of the feedstock at multiple stages and value added by-products. This study focuses on one of the program crops, Simarouba glauca, as a test case. The conversion efficiency of the village-level, decentralised production model was assessed and compared with the theoretical biodiesel production efficiency. The study indicated that the field-level feedstock conversion efficiency was less than that of the lab-scale set up. However, the fuel qualities of the Simarouba glauca biodiesel were found to be of standards required for fuel designation. The study shows that there is a significant potential for improving the field-level feedstock conversion efficiency through technical improvements and best practices in oilseed collection, curing and conversion. The study offers a few programmatic and policy suggestions for such improvements.

Phosphorus leaching potential from compost amendments in a carbonatic soil

Composts are applied to carbonatic soils in south Florida to improve their physical characteristics and increase water retention. Blends of biosolids and municipal waste are often combined to increase the nutrient content of the compost. However, the high P content of some compost has led to concerns about the potential for P movement into shallow groundwater. Studies were conducted to determine the potential for P leaching in soil amended with biosolids, clean organic waste, and Bedminster composts. Bedminster was the most suitable of the composts used in terms of a lower potential for P leaching as a result of P sorption in the amended soil. Each compost-amended soil demonstrated a slight decrease in P leaching at 1 pore volume after simulated rainfall (21 cm). Pore volume was defined as the total volume in a column less the volume of solids. The high P content of the composts made it unlikely that additions of these materials to soil would improve P sorption capacity. However, Bedminster and clean organic waste did not significantly increase P leaching above that of the soil. Caution should be exercised when applying these composts because materials themselves contain an enormous amount of P that could be eventually transported into the groundwater.

Effect of soil amendments (composts) on water balance and water quality- Model Simulations

The nutrients loading from agricultural and urban areas have increased nutrient concentrations, particularly phosphorus, at the Everglades National Park (ENP). The soils in the region are mainly crushed limestone with low water holding capacity, high permeability, low organic matter, and low fertility. The Everglades-Agro-Hydrology Model (EAHM) has been developed to evaluate the impact of agricultural practices on crop production, water balance and the fate and transport of nutrients and pesticides. Considering the poor soil quality, the model simulation test indicated that the application of 90 to 134 T.ha-1 of compost annually will result in an increase in soil-water content, crop yield, and reduced water seepage below the root zone, thus reducing the potential for nitrogen and Atrazine to leach into groundwater.