Microorganisms, in particular bacteria, play far more important ecological roles in natural environments than their small sizes would suggest. The environment for bacteria is everything that surrounds and sustains them including air, plant, animal surfaces and interiors, soil, water and even the micrometer sized organic particles. Thus, from an ecological perspective, bacteria are integral parts of the organismis communities that interact variously with each other and between other, higher and lower forms of life. These interactions in any ecosystem are of greater significance both in terms of ecological dynamics and stability. Some microbes are autotrophic, capable of generating new organic matter. However, most microbes, in particular bacteria, are heterotrophic. Heterotrophic bacteria are largely responsible for biodegradation and recycling of organic matter. Thus, they are intimately involved in biogeochemical reaction of the key elements of living systems viz. C, H, N, S, P, O in addition to a few trace elements. In simple terms, biogeochemical reactions are all those changes and element undergoes in its oxidation state as it moves through an ecosystem, in and out of organisms. Microbiology is a many faceted science. Its understanding is essential for a better appreciation of ecological and technological events to which microbes are intimately linked. Efficient and economically beneficial industrial applications of microbes have been possible by understanding the basic ecology, physiology, biology and biochemistry of microbes. The results of these studies on the usefulness of marine luminous bacteria in marine pollution pre-screening, the direct viable counts of bacteria in sensing marine environmental pollution stress are reported.