FRESHWATER CULTURE MEDIA

INTRODUCTION Various culture media have been developed and used for isolation and cultivation of freshwater algae. Some are modifications of previous recipes to meet a particular purpose, Some are derived from analysis of the water in the native habitat, Some are formulated after detailed study on the nutrient requirement of the organism Some are established after consideration of ecological parameters.

Materials Chemicals The most reagent grade salts and nutrients contain levels of trace metals or other contaminants that may inhibit oligotrophic species. In addition, trace metal impurities in major salt solutions prepared from reagent grade chemicals may exceed the nominal metal concentrations of some media. Equipment Certain minimal equipment (glassware, plasticware, pH meter), an autoclave, filtration equipment, disposable membran filters, sterile water, an ultrasonic washer, and refrigerator are necessary for preparing and maintaining stock solutions and culture media Glassware Water The earliest investigators used spring water because tap water and distilled water were heavily contaminated with metals.

Agar Ordinary agars consist of agarose and agaropectin that are contaminated with various impurities, and some agars contain water-soluble lytic agents against cyanobacteria. Soil A liquid soil extract or solid particulate soil is used for culturing algal species when precise knowledge of nutritional requirements in not necessary and when maintaining normal morphology is critical. Recommended sources for good soils are gardens or greenhouses where the soil has not been exposed to chemicals, undisturbed deciduous forests, and grasslands that have not been tilled or grazed. The soil should be of the loam type. For certain rare or sensitive algae, it is sometimes possible to obtain good soil near the lake or pond where they grow naturally. The soil must be taken from above the water level.

Stock Solutions Media are generally compose of three components: Macronutrients, trace elements (EDTA) and vitamins (vitamin B1,B12, and biotin), all three are often prepared as stock solutions. Stock solutions should be stored in tightly sealed glassware or plasticwre to avoid alteration of the initial concentration due evaporation. Refrigerate (4OC) or freeze stock solutions when not in use.

General Methods of Preparation of Media Freshwater media are divided broadly into 3 categories: 1. Synthetic Designed primarily to provide simplified, defined media, for both careful experimental studies and routine maintenance of strains. Ex: Bold’s Basal Medium, BG-11 medium, Chu #10 medium, WC medium, and v medium. 2. Enriched Adding nutrients to natural lake or stream waters or by enriching a synthetics medium with soil extract, plant extracts, yeast extract, etc. Ex: Alga-Gro lake water medium, Audouinella medium, Diatom medium, VS medium, Modified Porphyridium medium, Malt medium, and Polytoma medium. 3. Soil water

Solidified Media : Agar Standard Nutrified Agar Klebs and Tischutkin were among the first to use culture media solidified with agar for cultivating algae, and nutrified agar is still very useful for growing most freshwater algae. A small inoculum of cells is spread onto the surface of the agare, and generally the cells grow slowly on the agar surface. Nutrified Agar Pour Plates Some algae will not grow on the surface of agar , but they will grow if embedded in the agar. For algae that are sensitive to higher temperatures, low-gelling-temperature agarose or ultra low gelling temperature agarose can be used.