John H. Lobos

Acidiphilium organovorum sp. nov., an acidophilic heterotroph isolated from a Thiobacillus ferrooxidans culture

Acidiphilium organovorum sp. nov. is a gram-negative, heterotrophic bacterium that was isolated from a culture of Thiobacillus ferrooxidans which had been grown autotrophically on FeSO4-basal salts medium for several years. Purification of A. organovorum was carried out on a 1.0% glucose-basal salts medium (pH 3.0) solidified with agarose. Growth was enhanced by adding high concentrations of glucose (0.5 to 2.0%) and by supplementing the medium with yeast extract and trace amounts of FeSO4. However, these supplements were not necessary for growth. A wide variety of organic compounds were suitable substrates for growth, but inorganic forms of reduced sulfur or ferrous iron were not. Doubling times of 2.5 h and cell densities of >2 × 1010cells per ml were obtained at the optimal temperature of 37°C and pH 3.0. The guanine-plus-cytosine content of the deoxyribonucleic acid was 64 mol%. A. organovorum contains at least three distinct plasmids; one of these plasmids is larger than 30 kilobase pairs, and two are smaller than 4.0 kilobase pairs. Homology studies in which we compared the total deoxyribonucleic acid of A. organovorum with the total deoxyribonucleic acids of Acidiphilium cryptum and several Thiobacillus species indicated that A. organovorum is most closely related to A. cryptum. A. organovorum can be differentiated from Thiobacillus acidophilus by its higher temperature optimum, its faster growth rate, and its inability to utilize reduced forms of sulfur or iron as energy sources. The abundant cell growth that occurs in a medium which either is rich in organic compounds or completely lacks nutritional supplements distinguishes A. organovorum from A. cryptum. The other physiological and genetic characteristics which we examined are in close agreement with the characteristics of members of the genus Acidiphilium. The type strain of A. organovorum is strain ATCC 43141.

A Phylogenetic Analysis of Aerobic Polychlorinated Biphenyl-Degrading Bacteria

Several bacterial isolates were characterized based on their abilities to degrade specific polychlorinated biphenyls (PCBs) and their 16S rRNA gene sequences. The members of one group of bacteria consisting of Alcaligenes species, including the PCB-degrading bacterium Alcaligenes eutrophus H850, had strong abilities to degrade a broad range of PCBs but not the di-para-chlorine-substituted congeners. The members of another group, which included the PCB-degrading bacterium originally classified as Corynebacterium sp. strain MB1, had strong abilities to degrade di-para-chlorine-substituted PCBs. These bacteria were most likely different members of Rhodococcus species.

The use of genetic probes to detect microorganisms in biomining operations

SummaryMicroorganisms are currently used for the recovery of copper from mining dumps of low-grade ore. One of the most important microorganisms involved in copper-solubilization isThiobacillus ferrooxidans, although many other microbial genera are also thought to be implicated. A mining dump poses some special problems for the industrial microbiologist because it represents a non-sterile and heterogeneous substrate. Consequently, to enhance our knowledge of the role of microorganisms in metal recovery we must identify the indigenous microorganisms and understand their respective contributions to the process. In addition, when a superior strain of microorganism is developed in the laboratory, by genetic engineering or by other means, we must have a method to evaluate the maintenance of such a strain in the mining dump. In this paper, we describe DNA homology studies, using dot blot and Southern blot analysis of hybridizations of both whole genomic DNA and cloned DNA sequences, to identify and enumerate several bioleaching microorganisms. We demonstrate that it is possible to identify different species of microorganisms and, in one case, to discriminate between different strains of a single species. It is also possible to identify and quantitate certain species in a mixed culture. DNA hybridization analysis has several advantages over the more conventional bacteriological methods of identification, especially in a complex bioleaching situation.