BIODIVERSITY OF CYANOBACTERIA IN FRESH WATER PONDS OF PUDUKKOTTAI DISTRICT, TAMILNADU, INDIA

Cyanobacterial species (blue-green algae) constitute the major part of the phytoplanktonic biomass during the summer in freshwater ponds. The aim of the research work was to study the biodiversity of cyanobacteria among 20 different freshwater ponds of the Pudukkottai district of Tamil Nadu, India. The morphological identification of cyanobacterial species was carried out using a trinocular microscope. The results showed that the maximum number of cyanobacterial species belonged to Oscillatoriaceae, Nostocaceae, Microcystaceae, Scenedesmaceae, and Desmidiaceae families. Among 25 different families of Cyanobacteria about 42 distinct species were identified. These results showed that the freshwater ponds of the Pudukkottai district have an abundance of cyanobacteria species.


Introduction
Fresh water ponds enclose a specific ecosystem with respect to the pond setting, and it's comprised of numerous plants, aquatic animals and bacteria [1]. Each element of freshwater pond's ecosystem is always dependent on the other elements and organisms for their survival The primary producers of fresh water ponds are phytoplanktons, the secondary are zooplankton and the ecosystem also contains decomposers [2,3]. Cyanobacteria (blue-green algae) are widely distributed in fresh water ponds and are capable of performing both carbon assimilation and N2 fixation, thereby enhancing productivity in a variety of environments. They secrete a number of biologically active substances rather than nitrogen fixation [4]. Tropical conditions prevailing in India provide a favorable environment for the abundant growth of these organisms in the fresh water ecosystems [5,6]. They constitute the greater part of the phytoplanktonic biomass during the summer [7,8]. Certain species of Cyanobacteria in the genera Anabaena, Aphanizomenon, Microcystis, and Oscillatoria most often form extensive and persistent blooms in freshwater aquaculture ponds [9]. The development of Cyanobacterial blooms is favored under conditions when the availability of nitrogen is limited compared to phosphorus, and in warm water temperatures. Under those conditions, dominance of phytoplankton communities by cyanobacteria is the result of certain unique physiological attributes (in particular, N2 fixation and buoyancy regulation) that allow Cyanobacteria to compete effectively with other phytoplankton. The ability to regulate cell buoyancy through environmentally-controlled collapse and reformation of intracellular gas vacuoles is perhaps the primary reason for the frequent dominance of aquaculture pond phytoplankton communities by Cyanobacteria [10], [11].
Cyanobacteria are always found in close association with a diverse array of microorganisms, including eubacteria, fungi, and protozoans [12]. Cyanobacteria are very important organisms for the health and growth of many plants. Cyanobacteria play an important role in the nitrogen cycle. They are one of very few groups of organisms that can convert inert atmospheric nitrogen into an organic form, such as nitrate or ammonia and also they provide oxygen as a by-product of photosynthesis [13], a food source for other organisms such as zooplankton, insects and snails, and in the case of larger filamentous algae, a habitat for small animals [14]. The most common toxic Cyanobacteria in fresh water are Microcystis spp., Cylindrospermopsis raciborskii, Planktothrix (syn. Oscillatoria) rubescens, Synechococcus spp., Planktothrix (syn. Oscillatoria) agardhii, Gloeotrichia spp., Anabaena spp., Lyngbya spp., Aphanizomenon spp., Nostoc spp., some Oscillatoria spp., Schizothrix spp. and Synechocystis spp. This study presents the isolation and characterization of different types of Cyanobacterial species in fresh water ponds of Pudukkottai district, Tamil Nadu, India.

Collection of samples
There are 20 different ponds in a different monthly intervals for a period ranging from Aug 2018 to Sep 2019 in Pudukkottai dictrict located in Tamil Nadu, India. Pond water samples were collected in sterilized bottles of 500 ml capacity at a depth of about 30 cm. The sample is fixed soon after collected and taken to the laboratory for analysis.

Morphological identification of Cyanobacteria
Morphological identification of Cyanobacteria was done by spreading a Cyanobacterial culture on glass slides using forceps. Culture were covered with glass cover slips and observed their size, shape, color and other features under low (10X) and high power (100 X) objective lens of Trinocular microscope.

Species identification of Cyanobacteria
Various species of Cyanobacteria present in fresh water ponds of Pudukkottai district were identified using the reference manual Cyanophyta by T.V. Desikachary and "Manual of freshwater algae of Tamil Nadu"by G. Mahendra Perumal and N. Anand (2009).

Isolation & identification of Cyanobacteria in fresh water ponds
Cyanobacterial species present in fresh water ponds of Pudukkottai district were identified and classified based on the reference manual. Nearly 25 different families of Cyanobacteria species were identified has been diverse in the fresh water ponds of Pudukkottai District. About 42 versatile species of Cyanobacteria belonging to 25 different families were found to reside in the freshwater ecosystem of Pudukkottai district. Each species has its own unique size and shape which distinguishes them to be classified under various families. Each and every species has its own significance in the ecosystem in which they live.

Conclusions
In any ecosystem, not a single species grow independently and indefinitely, because each and every species are interlinked and has cyclic transformation of nutrients. The physicochemical changes in the environment in which they reside might affect particular species and can induce the growth and abundance of other species, which leads to the succession of several species in a period of time. A large number of Cyanobacterial species has been isolated and classified into 42 different species belongs to 25 different families present in the 20 different fresh water ponds of Pudukkottai district, Tamil Nadu, India which shows the abundance of Cyanobacteria in fresh water ponds. (1)