Diseases and Management of Crops under Protected Cultivation

(Diseases and Management of Crops under Protected Cultivation)
Use of Biolog for Identification of Bacterial Plant Pathogens
R.P. Singh and Smita Puri
Department of Plant Pathology, G.B.P.U.A&T., Pantnagar- 263 145 (UK)
In recent years, popular methods for studying plant pathogens community structure were
based on the analysis of phospholipid fatty acids (PLFA) or denaturing/temperature gradient gel
electrophoresis (DGGE/TGGE) etc. The above-mentioned methods are based on molecular
assays. Measurements of physiological activity of microorganisms represent another approach,
allowing the study of different characteristics of microbial communities. The Biolog technique is
one of the methods which rely on measurements of utilizing different carbon substrates by
microorganisms. Measurements of substrate use enable qualifying microbial metabolic capabilities
and hence functional diversity of a microbial community.
The Principle of the Biolog Method - The Biolog plate’s method was first used to compare
metabolic activity of heterotrophic microbial communities from different habitats such as water, soil
and wheat rhizosphere. The technique is based on a redox system. Various types of plates are
used, but Biolog GN plates for gram-negative bacteria are the most popular ones. Biolog Microbial
Identification System is based on metabolic phenotypes. Biolog plates are plastic microtiter plates
containing 95 different carbon substrates in wells, and no substrate in one well which is used as
control. Among the 95 substrates one can distinguish a few groups of chemical compounds, for
example, carbohydrates, amino acids, carboxylic acids, amines, amides and polymers. Biolog is
based on the theory that a species of bacteria develops a unique metabolic finger-print on a set of
carbon sources and biochemicals. The cultured bacteria are tested for utilization of different
carbon sources and biochemicals, which are pre-filled and dried into a 96 well test plate.
Additionally, each well contains a colourless Tetrazolium redox dye, used to colorimetrically
indicate utilization of the substrates. Cells utilizing nutrient, respire and release energy which
reduces proprietary Tetrazolium dye to form a distinct purple colour. Biolog data collection
software is used to record the unique metabolic profile into the computer which can be compared
with thousands of profiles (corresponding to thousands of species) stored in the Biolog databases.
If the profile is matched, computer displays the identified species.
Biolog has designed proprietary microplates for identification of a wide range of microbes
up to species level, such as Gen III plate (for gram negative and gram positive aerobic bacteria),
AN plate (for anaerobic bacteria), YT plate (for yeast) and FF plate (for filamentous fungi). Nearly
2550 species are covered by Biolog for identification.
Application- It has been used for clean room analysis of microbial identification prevalent in
environment, industrial quality control in analysis of food and/or agricultural products, plant disease
diagnosis, veterinary, analysis of clinical samples including dangerous pathogens of human,
animal and plant origin, education and research involving general and applied microbiology.
Different types of Biolog plates- The Biolog GNplates have been designed for identification of
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