Annual Abundances, Diversity and Growth Potential of Gymnamoebae in a Shallow Freshwater Pond

ABSTRACT. Abundance and diversity of gymnamoebae were assessed at monthly intervals for one year in the sediment surface layer of a shallow, highly productive, freshwater pond located in northeastern United States using laboratory culture enumeration techniques. The range in total abundance was 81/ml in January to 1,568/ml in June (spring peak) and 1,813/ml in October (autumn peak). The latter is equivalent to over 1.8 million per liter, one of the highest values reported for gymnamoebae from a freshwater pond. Maximum diversity (H = 3.3) occurred in April, July, and August. The growth potential of the gymnamoebae was determined in laboratory cultures (20° C) containing only the pond water (control culture) and pond water emended with malt-yeast extract and glucose (nutrient culture) using pond water collected in December. The total abundance of gymanmoebae increased from 363/ml in the initial pond water sample to approximately 1,800/ml in each of the culture conditions in the first week. Therafter, abundances reached 5,678/ml (control culture) and 8,016/ml (nutrient culture) by the third week indicating the vigorous growth potential from winter standing stock.     

Production of Bean yellow mosaic virus resistant subterranean clover (Trifolium subterraneum) plants by transformation with the virus coat protein gene

Transgenic lines of subterranean clover were constructed that contained three different Bean yellow mosaic virus (BYMV) coat protein (CP) gene constructs; full-length CP, the core region of the CP, and full-length CP plus the 3′ untranslated region of the viral genome. Transgenic plants containing the full-length and core CP gene constructs showed high and moderate levels of BYMV resistance. Resistance was measured as a lack or amelioration of viral disease symptoms, which was correlated with a reduction in virus levels and yield loss. A range of different resistance phenotypes was observed. They included reduced infection rates, delay and reduction in local lesion development, and delay and reduction in severity of systemic symptom development. Resistance levels were not correlated with transgene mRNA levels and no transgene-encoded protein was detected in any of the transgenic lines. This is the first example of genetically engineered virus resistance in a clover.     

The control of organic matter on microbially mediated iron reduction and arsenic release in shallow alluvial aquifers, Cambodia

Microbes may play a key role in the mobilization of arsenic present in elevated concentrations within the aquifers extensively exploited for irrigation and drinking water in West Bengal, Bangladesh, and in other regions of South-East Asia. Microcosm experiments using Cambodian sediments (which are also representative of other similar reducing aquifers containing arsenic-rich waters) show that arsenic release and iron reduction are microbially mediated and demonstrate that the type of organic matter present, not necessarily the total abundance of organic matter, is important in controlling the rate and magnitude of microbially mediated arsenic release from these aquifer sediments. The possible role of naturally occurring petroleum in stimulating this process is also demonstrated. In addition to acting as an electron donor, certain types of organic matter may accelerate arsenic release by acting as an electron shuttle, indicating a dual role for organic matter in the process. The results also suggest that the fine-grained sediment regions of these aquifers are particularly vulnerable to accelerated arsenic release following the introduction of labile organic carbon.     

In situ ecological development of a bacteriogenic iron oxide-producing microbial community from a subsurface granitic rock environment

The initial development and diversity of an in situ subsurface microbial community producing bacteriogenic iron oxides (BIOS) were investigated at the initiation of biofilm growth (2‐month period) and after a 1‐year period of undisturbed growth. Water chemistry data, samples of iron encrusted biofilm material and groundwater were collected from BRIC (BIOS reactor, in situ, continuous flow) apparatuses installed 297 m below sea level at the Äspö Hard Rock Laboratory (HRL) in south eastern Sweden. Comparisons between the BIOS BRIC system and an anaerobic control (AC) BRIC revealed that water mixing at the inflow leads to profuse development of BIOS related to a slightly elevated level of O₂ (up to 0.3 mg L^?1 at the transition zone between BIOS development and non‐development) and elevated Eh (>120 mV) in the first 70 mm of water depth. Decreases in dissolved and particulate iron were connected to the visible appearance of BIOS biofilms. The basic phylogenetic diversity of this site was evaluated using amplified ribosomal DNA restriction enzyme analysis (ARDRA), denaturing gradient gel electrophoresis (DGGE) and partial sequencing of 16S rDNA. From 67 clones that were positive for 16S rDNA inserts, a total of 42 different ARDRA profiles were recognized, representing four bacterial phyla and 14 different metabolic lifestyles. DGGE profiles indicated that there are differences in the representative bacteria when considering either BIOS biofilms or groundwater. DGGE also indicated that the DNA extraction protocols and any polymerase chain reaction biases were consistent. Bacterial metabolic groups associated with indirect metal adsorption and reduction along with bacteria utilizing many alternative electron acceptors were strongly represented within the clones. This study indicates that the microbial diversity of BIOS is greater than previously thought.