Growth characteristics of the aerobic bacterial strain Arthrobacter citreus BI-100 in mineral salts medium with γ-hexachlorocyclohexane (γ-HCH) as the sole source of carbon and degradation of γ-HCH by the strain are reported. The highest yield of the bacteria is observed at a γ-HCH concentration of 100 mg/L. At this concentration, the bacteria entered the exponential phase of growth without any lag. At 8 h of growth, no residual HCH, but its metabolites, was detectable in the medium. The bacterium attained its stationary phase at 48 h and at 72 h; no metabolite of γ-HCH could be detected by gas chromatography. Six metabolic intermediates of γ-HCH produced by A. citreus BI-100 at different periods of growth were characterized by using gas chromatography-mass spectrometry and high-performance liquid chromatography, which furnished evidence for the presence of γ-1,3,4,5,6-pentachlorocyclohexene, tetrachlorocyclohexene, trichlorocyclohexa-diene, 2-chlorophenol, phenol, and catechol, among others.
The objective of this study was to determine the genetic relatedness among the Cercospora and Pseudocercospora species closely related to Cercospora apii by using a polymerase chain reaction/restriction fragment length polymorphism (PCR/RFLP) analysis of the internal transcribed spacer (ITS) region. A single PCR fragment (about 550 bp) was obtained from all Cercospora species categorized as the C. apii-group, Pseudocercospora purpurea, Pseudocercospora conyzae, and Pseudocercospora cavarae. Cercospora caricis yielded a 680 bp PCR fragment. The similarity in the PCR fragment size and RFLP profiles among the C. apii-group isolates, including Pseudocercospora purpurea, and Pseudocercospora conyzae strongly suggests that these species are conspecific. Synonymy with C. apii (lectotype) at a subspecific rank has been proposed. Amplified ITS regions of genomic DNA extracted from spinach leaves showing 12 and 23% leaf spot disease symptoms caused by Cercospora beticola yielded two PCR fragments (i.e., one from the fungus and one from the host plant) and were resolved by electrophoresis of the PCR product in 3% LMP agarose. Digestion of the total PCR product with HinfI restriction enzyme yielded RFLP profiles similar to those obtained from amplified DNA from the causative agent, C. beticola. The method described in this preliminary study offers rapid detection and diagnosis of fungal infections in plants for disease prediction and management and screening of plant materials for quarantine purposes.
A soil consortium was tested for its ability to degrade reformulated gasoline, containing methyl tert-butyl ether (MTBE). Reformulated gasoline was rapidly degraded to completion. However, MTBE tested alone was not degraded. A screening was carried out to identify compounds in gasoline that participate in cometabolism with MTBE. Aromatic compounds (benzene, toluene, xylenes) and compounds structurally similar to MTBE (tert-butanol, 2,2-dimethylbutane, 2,2,4-trimethylpentane) were unable to cometabolize MTBE. Cyclohexane was resistant to degradation. However, all n-alkanes tested for cometabolic activity (pentane, hexane, heptane) did enable the biodegradation of MTBE. Among the alkanes tested, pentane was the most efficient (200 μg/day). Upon the depletion of pentane, the consortium stopped degrading MTBE. When the consortium was spiked with pentane, MTBE degradation continued. When the ratio of MTBE to pentane was increased, the amount of MTBE degraded by the consortium was higher. Finally, diethylether was tested for cometabolic degradation with MTBE. Both compounds were degraded, but the process differed from that observed with pentane.
Bacterial communities in groundwater collected from five different sites at the Kamaishi Mine were investigated by using denaturing gradient gel electrophoresis (DGGE). The bacterial cells in groundwater were collected on Millipore filters, and their nucleic acid was extracted by freeze-thaw cycles. A partial 16S rRNA gene was amplified by using a universal primer set by PCR. The PCR products were analyzed by DGGE. The band pattern of DGGE was essentially identical between two samples obtained from different depths in the same borehole (KH-1). Samples from the other sites differed from one another. The partial sequences of 16S rRNA genes (about 350 base pairs) isolated from bands were determined and analyzed for phylogenetic position. Almost half the sequences from two samples of the KH-1 belonged to the cluster of spore-forming, gram-positive sulfate reducer, Desulfotomaculum. The other bands also were related to those of obligate anaerobes. This suggests that the environment in both sites of KH-1 was highly anaerobic. Although only a few sequences were retrieved from the other sites, they were phylogenetically distanced from known isolates.