Preface Emergence of new pathogens and increasing antibiotic resistance among existing microorganisms has become a major problem to the humanity. The time has come to get rid of this problem and the biologists should rise to the occasion to discover novel sources of medicine. Taking this into consideration, a global attention has arisen towards finding new chemicals, with lead structures, which either directly or after small modifications can be used for development of new drugs. The advantage of microorganisms, which can be cultured, such as cyanobacteria, is that a sustainable supply of desired metabolites can be achieved, which is not always possible for a product derived from sources based on macro-organisms. Moreover, cyanobacteria promise greater opportunities with all relatively inexpensive and easier approaches against some expensive and technically complex methods presently in use for new drug discovery, such as – combinatorial chemistry and molecular biotechnology. The various properties of cyanobacteria include antibacterial, antifungal, anti-HIV, anticancerous and antialgal characteristics. Present study deals with some cyanobacterial species from Nostocaceae, Oscillatoriaceae and Stigonemataceae. Each culture was harvested and spent medium was collected by filtration of the biomass. Hexane, ethyl acetate, dichloromethane and methanol were used as the solvents for obtaining the extracts from biomass of each culture. The extracts and spent medium thus obtained were investigated for antibacterial activity against selected bacterial strains.

Some cyanobacteria (Blue-green algae) like Nostoc are known to work as one of the two coponenents (photosynthetic partner or phycoboint) of lichens. The second partner of lichen is a lichen fungus or mycobiont. The lichens have not been described as a therapeutic agent in Charak Samhita, the monumental work on materia medica prepared by great Acharya Charak and his group in India more than three thousand years ago. However, these have been used in folklore medicine in many countries of the world and have been regarded to bear antibacterial properties (Katiyar and Katiyar, 2009). They are found in tundra even, the treeless plain of the arctic regions of Russia, Siberia, marshy in summer and frozen hard in winter. It is common to see gunny bags full of lichens for sale in the Masala market near Kesa House, Express Canal Road, at Kanpur. They also comprise a part of meat masala (spices for meat). There are references that Raja (King) Todarmal studied algae in relation to purification of water. However, the search for antibiotics began in the late 1800s, with the growing acceptance of the germ theory of diseases; a theory which linked bacteria and other microbes to the causation of a variety of ailments. As a result, scientists began to devote time searching for drugs that would kill these disease-causing bacteria.

Cyanobacteria have been identified as one of the most promising groups of organisms from which novel and biochemically active natural products are isolated. Cyanobacteria such as Microcystis, Anabaena, Nostoc and Oscillatoria produce a great variety of secondary metabolites. The only group comparable to cyanobacteria is actinomycetes, which has yielded a tremendous number of secondary metabolites. The rate of discovery from traditional microbial drug producer like actinomycetes, which is in the focus of pharmaceutical research for decades, is decreasing and it is the time to turn to cyanobacteria and exploit their potential. Recently, there has been an increasing interest in cyanobacteria as a potential source of new drugs (Glombitza and Koch, 1989; Schwartz et al., 1990). This is of paramount importance to fight increasingly resistant pathogens and newly emergent diseases (Hayashi et al., 1994). Cyanobacteria are photosynthetic microorganisms that have flourished on earth for more than 3 billion years with some genera showing only minor morphological changes since that time (Hagmann and Juttner, 1996). The medicinal and nutrient qualities of cyanobacteria were first appreciated as early as 1500 BC, when Nostoc species were used to treat gout, fistula and several forms of cancer (Pietra, 1990; Bladon, 2002; Liu and Chen, 2003).

Cyanobacterial species Cyanobacterial species viz., Anabaena variabilis, Anabaena fertilissima, Nostoc muscorum, N. punctiforme, N. linckia, N. commune, Spirulina platensis, Westiellopsis prolifica and Hapalosiphon sp. were obtained from National Center for Conservation and Utilization of Blue-green Algae, Indian Agricultural Research Institute, New Delhi. Cultures were maintained in BG-11 growth medium throughout the study in the laboratory.

Culture Media and Reagents The media used throughout the study were procured from Hi- Media Laboratories, Mumbai, India and the chemicals used were procured locally. Composition of each medium is as follows:

Nine cyanobacterial strains viz., Anabaena variabilis, A. fertilissima, Nostoc muscorum, N. punctiforme, N. linckia, N. commune, Spirulina platensis, Westiellopsis prolifica and Hapalosiphon sp. were cultured in the laboratory. The growth curve for each culture was studied by growing them in Erlenmeyer flask using BG-11 growth medium. They were examined to determine the early stationary phases of their life-cycle, which are believed to be the most appropriate period for the production of secondary metabolites by an organism. After 23-25 days of incubation period, each culture was harvested and spent medium was collected by filtration of the biomass. Hexane, ethyl acetate, dichloromethane and methanol were used as the solvents for obtaining the extracts from biomass and spent medium of each culture which were then investigated against five pathogenic bacteria viz., Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae and Salmonella typhi. Antibacterial activity of different cyanobacterial sp. has been shown in various tables.

In the present investigation, nine cyanobacterial species viz. Anabaena variabilis, Anabaena fertilissima, Nostoc muscorum, Nostoc punctiforme, Nostoc linckia, Nostoc commune, Spirulina platensis, Westiellopsis prolifica and Hapalosiphon sp. were tested for their activity pattern against some selected bacterial species.   Each cyanobacterial species was initially subjected to determine the early stationary phase of their life-cycle, which is believed to be the most appropriate period for the production of secondary metabolites by an organism. The growth curve for each cyanobacterial species was prepared by culturing them in BG-11 growth medium. Optical densities (OD) recorded at 650 nm were plotted against number of incubation days for each cyanobacterium. After 23-25 days of incubation period, each culture was harvested to obtain the biomass and spent medium, which were then subjected to process of extraction by using various solvents viz., Hexane, ethyl acetate, dichloromethane and methanol. The extracts and spent medium thus obtained were then investigated for antibacterial activity against five pathogenic bacteria including Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pnumoniae and Salmonella typhi.

Present work was aimed to determine the antibacterial activity and minimum inhibitory concentration (MIC) of active crude extracts of selected cyanobacterial species. Nine cyanobacterial strains viz. Anabaena variabilis, A. fertilissima, Nostoc muscorum, N. punctiforme, N. linckia, N. commune, Spirulina platensis, Westiellopsis prolifica and Hapalosiphon sp. belonging to family; Nostocaceae, Oscillatoriaceae and Stigonemataceae were selected from the herbarium of Indian Agricultural Research Institute, New Delhi, and maintained in BG-11 growth medium throughout the study in the laboratory.

The objective of the present investigation was to evaluate the antibacterial properties of cyanobacterial species viz., Anabaena variabilis, Anabaena fertilissima, Nostoc muscorum, Nostoc punctiforme, Nostoc linckia, Nostoc commune, Spirulina platensis., Westiellopsis prolifica and Hapalosiphon sp. against some pathogenic species including Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pnumoniae and Salmonella typhi. The following are the major findings of the study.     •    Extracts prepared in methanol were found more active as compared to ethyl acetate, hexane and dichloromethane.       •    Antibacterial activity of extracts varied with the test organisms. Maximum antibacterial activity was shown against Staphylococcus aureus followed by Escherichia coli, Pseudomonas aeruginosa and Salmonella typhi. Klebsiella pneumoniae was found to be least susceptible against all tested cyanobacterial extracts.     •    Antibacterial activity was observed against both Gram-positive and a spectrum of Gram-negative bacteria by almost all the cyanobacterial species examined in the present study except Westiellopsis prolifica where activity was observed only against S. aureus, a Gram-positive bacterium.

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INDEX A Acetylated sulfoglycolipid 173 Acutiphycins 13, 29 Aerial 173 Aeruginosin 16, 173 Akinete 46, 173 Algaecides 173 Amino acids 5 Anabaena 16, 17, 21, 29, 30, 33, 44, 45, 47, 48, 97, 99, 100, 108, 109, 110, 111, 127, 128, 137, 138, 139, 142, 145, 146, 147, 151, 152, 157, 162, 163, 169, 174, 177, 178, 181, 184 Anabaenopeptin 165, 174 Anthraquinone 33, 174 Antibacterial 1, 6, 11, 20, 22, 27, 28, 30, 31, 32, 33, 34, 35, 58, 92, 97, 108, 110, 112, 114, 116, 118, 120, 122, 124, 137, 138, 139, 140, 141, 142, 143, 145, 146, 148, 155, 156, 157, 158, 160, 161, 162, 164, 166, 167,