S. Matei, Gabi Mirela Matei, Amelia Anghel


The presence of humus enhances and stimulates the growth of micro- and macro-level biodiversity of flora and fauna. It also appears consisting of organic residues and by-products which contain microbial type bio-synthesized substances as prehumic substances.

Prehumic compounds are made up of carbohydrates, lipids, proteins, amino acids, DNA, etc. Their importance appears well highlighted while the balance between formation and microbial decomposition of humus is disrupted, their concentration being strongly influenced by the dynamics of soil processes mediated by microorganisms.

To assess exometabolites of the edaphic microflora, as the main source of biosynthetic precursors of humus, 66 microorganisms were initially isolated to set up a base wide enough for analysis and selection. Microorganisms belonging to 11 genera have been identified on the basis of morphological and biochemical tests. Strains producing colouring exometabolites were selected and isolated on PDA and Topping media (yellow, yellow-green by bacterial isolates of genera Streptomyces, Azotobacter and Xanthomonas, or green-orange, red by bacterial isolates of genera Pseudomonas and Streptomyces). Isolates 7 and 5 of Bacillus spp. had the highest content of brown compounds. Indole test performed on bacterial isolates belonging to the genera Streptomyces, Bacillus, Pseudomonas, Azotobacter, and Xanthomonas were positive for the 3 bacterial isolates of Azotobacter (10, 11 and 12). Isolates belonging to the genus Pseudomonas (8 and 9) had nitrate reductase activity, those belonging to the genera Bacillus and Azotobacter had a variable response on this activity, and isolates of genera Streptomyces and Xanthomonas showed no nitrate reductase activity. The highest content of polysaccharide compounds was synthesized by isolates 9 of Pseudomonas sp., 12 of Azotobacter sp. and 5 of Bacillus sp. Polyphenolic compounds were excreted in large quantities by isolates 6 (Bacillus sp.), 8 (Pseudomonas sp.) and 11 (Azotobacter sp).  Among isolates tested, the isolate 9 of Pseudomonas sp. was the most active in biosynthesis of protein compounds.

Understanding the complexity of soil microorganisms extracellular matrix will allow better management for humus regeneration, the biologically-mediated nutrient circuit and soil health.

Full Text:



Bailey I., and Scott, F., (1994). Diagnostic Microbiology, 9th ed. St. Louis, Mo., Mosby, 900pp.

Bergey, D.H., Holt, J.G., 1994. Manual of Determinative Bacteriology. 9th Edn, Baltimore: Williams and Wilkins. U.S.A., 787pp.

Campbell, W.H., Song, P., Barbier, G.G., (2006). Nitrate reductase for nitrate analysis. Environ Chem Lett 4, 69–73

Domsch, K.H., Gams, W., (1970). Fungi in agricultural soils. Vol. 1-2, eds. T&A Constable Ltd.Edinburg,London, 290 pp.

Dubois, M., K.A. Gilles, J.K., Hamilton, P.A., Rebers, F., Smith, (1956). Colorimetric method for determination of sugars and related substances. Analytical Chemistry 28, 350–356.

Dufossé, L. (2006). Microbial production of food grade pigments. Food Technol. Biotechnol. 44(3), 313–321.

Keneni, A. and Gupta, V.K., (2011). Characterization of a Red bacterium strain isolated from root nodule of a Faba Bean (Viciafaba L.) for Growth and Pigment production. J. Advanced Laboratory Research in Biology 2(3), 138-146.

Pohlon, E., Ochoa Fandino, A. and Marxsen J., (2013). Bacterial community composition and extracellular enzyme activity in temperate stream bed sediment during drying and rewetting PLoS ONE 8, e83365.

Ramasamy, A. and Manokaran, K., (2015). Screening and Isolation of pigment producing Actinomycetes from soil samples. International Journal of Biosciences and Nanosciences 2(2), 24-28.

Shubhangi, A Rajguru, Neha Sawant, Akshayaveni Valmiki, Padma V Deshmukh (2015). Isolation and identification of pigment producing bacterial isolates from different terrestrial habitats in Thane district, India. World journal of pharmacy and pharmaceutical sciences 5(1), 618-628.

Singleton, V.L., and Rossi, J.A., (1965). Colorymetry of total phenolics with phosphomolybdic-phosphotungstic acid reagents. Amer. J. Enol. Viticult. 16, 14458.

Watanabe, T., (2002), Pictorial Atlas of Soil and Seed Fungi Morphologies of Cultured Fungi and Key to Species. Second Edition. CRC Press LLC, 455pp.



  • There are currently no refbacks.

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 International License.