Cultured diversity of anoxygenic phototrophic purple bacteria of diverse habitats of India

Abstract

Microbial diversity constitutes the most extraordinary reservoir of life in the biosphere and it is the key to human survival and economic well being and provides a huge reservoir of resources which can be utilized for our benefit. The microbial diversity of the Indian subcontinent is one of the richest in the world owing to its vast geographic area, varied topography and climate, and the combination of several biogeographical regions. Though India is recognized as a one of the top 12 mega diversity regions of the world, prokaryotic diversity is very little studied in our country and the situation is even worse in studying the diversity of an important group of bacteria called Anoxygenic Phototrophic Bacteria (APB), which has a lot of biotechnological potentials (Sasikala and Ramana, 1995). Based on sulfur metabolism, APB are broadly classified into four groups: Purple sulfur bacteria (PSB), Purple nonsulfur bacteria (PNSB), Green sulfur bacteria (GSB) and green nonsulfur bacteria (GNSB). These are physiologically and phylogenetically diverse group of bacteria with multiple colours, perform photosynthesis in the absence of air and without producing oxygen in the presence of light. They contain several types of bacteriochlorophylls and a variety of carotenoides as pigments, which function in the transformation of light into chemical energy. They are widely distributed in most of the habitats including extreme environments. Purple bacteria were extensively studied compared to green bacteria because green bacteria are obligate anaerobes, whose isolation is more complex than that of purple bacteria. These bacteria arebeing commercially used since many years for several purposes, such as bioremediation, hydrogen production, enzymes, hormones, carotenoides, ubiquinones, waste water treatment, single cell protein, aqua feed and etc. The study of bacterial diversity consists of classification, nomenclature and identification. However, the methods used in the bacterial taxonomy are being improved since their invention.