Air, the harbinger of life, one of the major ingredients of life support system, has become a serious threat to life of all living organisms including human beings because it is being loaded with several kinds of pollutants. The activities of modern world had been responsible for these changes in the atmosphere.
In addition to chemical pollutants, biological materials such as pollen, bacteria, viruses and spores are also present and are responsible for deteriorating quality of air. Bacteria play an important role in the geochemical cycle. They could be used for monitoring pollution and for removing/reducing pollution load as well. Bacteria tend to acquire genetic components for these processes and environmental forces .select the fittest organisms. In this manner bacteria varies from one environment to another and tend to be unique to an area. The aim of this study was to screen the phenotypic and genotypic characters of airborne bacteria isolated from different sites of Karachi city.
During this study four sites were selected for the isolation of airborne bacteria, these sites were Karachi University, Gaddani (Ship breaking area), Tanneries at Korangi sector 7-A and Civil Hospital. 55 pure strains were isolated from these sites, they were identified, gram stained and their resistance to various antibiotics and metals were studied. Most of the strains were found to be resistant to antibiotics and heavy metals, which indicated antibiotics and metal pollution in those sites.
On the basis of genotypic characteristics the strains were screened for reduction, accumulation and solubilization activity against heavy metals. Among the isolated strains CMG821 (Pseudomonas 'sp.) showed accumulation of copper salt, whereas in CMG480 (Cucurbit yellow vine disease bacterium) aerobic and anaerobic reduction of chromate was observed. Analysis of cell sections using transmission electron microscopy with energy dispersive X-ray analysis (EDAX) showed intracellular copper in CMG821 (Pseudomonas sp.) but CMG480 (Cucurbit yellow vine disease bacterium) precipitated chromate extracellularly.
CMG8I4. (Klebsiella sp.), CMG818 (Pseudomonas sp.), CMG823 (Pseudomonas sp.) and CMG826 (Pseudomonas sp.) showed metal solubilization activity. Among these CMG814 was found to have plasmid DNA of 9.9kb and 7.5 kb The plasmids were successfully transferred to E.coli J-53 and JM-I09 nonsolubilizing strains by conjugation and transformation. The zone of solubilization were formed by the transformants and transconjugants as well.
Tn mutants of CMG823 (which did not show the presence of plasmid) were produced these mutants lacked the solubilizing activity; this suggested that perhaps the solubilizing genes (Sol+) were present on chromosomes in this strain. The results of tn mutants, transformants and transconjugants have suggested that the solubilizing genes are perhaps spread on both chromosomes and plasmid and their location varies in various strains. To conclude this study has produced a collection of air-borne bacterial strains. This collection may also contribute towards discovery of novel species, native to this area and they could later on be exploited for bioremediation.