The study of the rhizosphere of Calotropis gigantea revealed that during all Its stages of growth the microbial population in the rhizosphere was higher than that occurring in the control soil. The bacterial, actinomycetal and mould populations showed their individual characteristic variations proving that the rhizosphere, of each plant, is a special zone of microbial activity. These population changes were accompanied by a rhizosphere effect, the degree of which varied with the development of plant. The high count of actinomycetes in the rhizosphcre, a factor -which led to this systematic study was established to be caused by a Nocardia sp. dependent upon glutamate for it's growth. This Nocardia sp. showed antibiotic activity against a culture of Saccharomyces cerevisiae and a yeast sp. flourishing well in the soil away from the rhizosphere influence. The reason(s) for this unusual association of a plant with a Nocardia sp. remains to be settled. The HTPI method proved useful in the isolation of actinomycetes from the rhizosphere. It facilitated equally well in the isolation of the heat-resistant types (mostly spore formers) of microorganisms occurring in rhizosphere. All the isolated actinomycetes strains were found to be pectinolytic.

The antibacterial activity of 112 mushroom cultures from India was screened, and showed antibacterial activity in 18 cultures belonging to 11 genera. Good antibacterial activity of 9 species from the genera Amanita, Claudopus, Lepista, and Tricholoma was compared, and antibacterial activity was reported for the first time for Claudopus byssisedus and Amanita foetens species. Based on fast rate of growth, easy availability, cultivability, and edibility of the mushroom, in addition to a very low minimum inhibitory concentration (MIC), the strain of Lepista nuda was finally selected for further studies and was found to possess a MIC of 0.0042 μg/ml against Staphylococcus aureus and required a pH of 5.2 and temperature of 25°C for maximum production of the antibacterial substance(s). The water-soluble antibacterial substances extracted from the culture filtrate of L. nuda were found to be thermostable and acidic and were identified on the basis of ultraviolet (UV) absorption spectra as polyacetylenic compound(s).

Spermidine was found to be the predominant polyamine in all the acidophilic as well as neutrophilic strains of chemolithotrophic iron- and sulphur-oxidizing bacteria and associated organotrophic cultures inhabiting a copper mining ecosystem. Adaptation of neutrophilic Thiobacillus thioparus strain to pH 5.0 was found to increase the spermidine content of the cells 2.3 times while the biomass yield decreased by 50%. However, exogenous supplementation of spermidine could restore the biomass yield to levels obtainable at pH 7.0. These observations indicate that spermidine plays a significant role in adaptive behaviour of microorganisms in natural ecosystems, especially under acid conditions.

Microbial mining of copper sulphide ores, has been practiced on an industrial scale since the late 1950s. Since then, advances in microbial mining and the role of microorganisms involved in solubilization of metals have assumed commerical importance. The fact that bioleaching processes save energy, have a minimum pollution potential and are able to yield value-added by-products make these processes invaluable. The metal extraction processes using microorganisms, which are currently in active use, concern copper and uranium bioleaching. Biobeneficiation is also applied at an industrial scale for recovery of gold from arsenopyrites. The developments in these processes during the last 15 years, with particular reference to developing nations, are reviewed. Information gathered on molecular genetics of these microorganisms should lead to a better understanding and control of microbial leaching processes. Areas still needing research to sustain economic expansion of microbial mining techniques are indicated.

Biometallurgical processing of minerals is a fast-developing science and is of considerable importance especially to nations like India where rapid industrialization has increased the domestic demand for metallic raw material which has to be satisfied by heavy imports. One of the ways of leading the country to self-sufficiency is to attempt to produce the metals from indigenously available low-grade/waste ores or beneficiate their quality using an appropriate technology like biometallurgy. We have developed a culture collection and data bank in respect of this technology in India for microbial leaching of copper and bioconversion of manganese. In this programme, 207 potentially-useful micro-organisms such as iron-, sulphur-and manganese-oxidizing bacteria were isolated from 60 copper and manganese mines in the country, and they were used for leaching copper and converting manganese to a better variety. These two processes were scaled-up to the 300-kg level and the isolated microorganisms were stored in an active, ready-to-use form by devising suitable preservation methods. Such a compilation of information on ores and cultures, with a centralized facility for supply of useful cultures, was referred as a ‘culture collection and data bank’. Various Indian mining industries have shown interest in trying these processes on a large scale at their mines, using the cultures and the data available from us.

Cultures of Thiobacillus ferrooxidans and Thiobacillus thiooxidans, used in biohydrometallurgical processes of economic importance, are very difficult to preserve by conventional methods. Hence, to preserve the cultures with their activity intact, various techniques were tried, after determining their respective activity in terms of Iron Oxidation Rate (IOR) and Sulfur Oxidation Rate (SOR). Among the methods tested, along with the recommended method of serial transfer in a liquid medium, were methods such as lyophilization, storage in a liquid nitrogen and mixing with sterile, inert carriers like lignite or chalcopyrite ores. After a period check-up at 4 months and 8 months storage, it was found that out of these methods, mixing with sterile ore followed by storage at 8°C, kept both types of activities intact. The temperature of storage was observed to have a definite effect on activity, in that when the preserved cultures were stored at 8°C, the activity was retained, whereas at 28–30°C (RT) storage, the activity of all the cultures preserved by various techniques, dropped significantly.

Fatty acids of 18 strains representing 10 species of Thiobacillus were extracted from whole cells and examined as methyl esters by gas-liquid chromatography. Both visual and quantitative comparison of the resulting chromatograms for the presence and relative amounts of major peaks allowed rapid differentiation between such closely related species as Thiobacillus neapolitanus and T. thioparus and of eight other species. Except for a feature common to all thiobacilli tested, T. thiooxidans, T. neapolitanus and T. thioparus each possessed a characteristic fatty acid methyl ester profile that was exhibited by all the strains of that species. Hence, the thiobacilli could be divided into three distinct groups. It was possible to use the gas-liquid chromatographic patterns of the cellular fatty acids for rapid identification or grouping of these microorganisms since the fatty acid composition of the genus Thiobacillus thus appeared to be of taxonomic significance.

During the stationary growth phase, the phospholipids of Thiobacillus neapolitanus consisted of phosphatidyl glycerol (PG), diphosphatidyl glycerol (DPG), phosphatidyl-N-monomethylethanolamine (PME) and phosphatidyl ethanolamine (PE) in increasing amounts. In general, the phospholipids increased to a maximum concentration during the stationary phase and then decreased in concentration. Individually, PG and PE increased to a maximum in late lag or early exponential phase and then decreased in concentration. DPG and PME increased during the transition between the exponential and the stationary phase and reached a maximum concentration in the stationary phase. In older cultures, a quantitative interconversion between PG and DPG and PE and PME was observed. A lyso-phospholipid compound also appeared in the late stationary phase.

Transport of ferrous iron by phospholipids, from various Thiobacillus species and commercial sources, was studied as a liquid membrane permeability phenomenon using a modified apparatus of Schulman. It was observed that phosphatidyl serine enhanced the iron transport at a considerably higher level than phosphatidyl glycerol, phosphatidyl ethanolamine or phosphatidyl choline in that order. No difference was observed in the iron transporting ability of the phospholipids from thiobacilli and the standard phospholipids. Phosphatidyl serine was found to have more cation exchanging properties under the given conditions, than any of the other phospholipids tested.

An extracellular complex was isolated from the culture filtrate of Ferrobacillus ferrooxidans grown on either iron or sulfur. The complex isolated from the culture filtrate of iron-grown cells was red with an absorption maxima at 500–510 mμ. This complex consisted of approximately 60% non-phosphorus lipid. Ferrous iron was exclusively associated with a lipopolysaccharide–phospholipid fraction of the complex. The sulfur complex unlike the iron complex contained approximately 70% phospholipid and was yellowish. On the basis of hexosamine and heptose values, less lipopolysaccharide appeared to be associated with the phospholipid fraction of the complex from sulfur-grown cells than from the iron-grown cells.

The chemoautotroph Ferrobacillus ferrooxidans like other gram-negative bacteria possesses a multi-layered cell envelope (Remsen & Lundgren 1966) which is believed to be involved in Fe++ ion oxidation-the primary energy yielding reaction of the organism (Dugan and Lundgren, 1965). This report presents a phase of our study concerning the characterization of phospholipids in membranes of F. ferrooxidans. Reports of phospholipids in other chemoautotrophs have been published (Schaeffer and Umbreit, 1962; Jones and Benson, 1965; Hagen, Goldfine, and Williams, 1966).

A comparison of pectinolytic properties of actinomycetes isolated from soils by the use of the High Temperature Pre-Incubation method and the conventional method has revealed the advantage of using, the former method for the isolation of pectinolytic species. This method thus holds promise of its exploitation for the isolation of the pectinolytic actinomycetes from any desired ecosystem.