An effective microorganism refers to any of the predominantly anaerobic organisms blended in commercial agricultural amendments, medicines, and nutritional supplements based on the trademarked product originally marketed as EM-1 Microbial Inoculant, aka Effective Microorganisms and EM Technology. These blends are reported to include:
- Lactic acid bacteria: Lactobacillus casei
- Photosynthetic bacteria: Rhodopseudomonas palustris
- Yeast: Saccharomyces cerevisiae
- Others: beneficial microorganisms that exist naturally in the environment may thrive in the mixture.
EM Technology is purported to support sustainable practices in farming and to improve and support human health and hygiene, compost and waste management, disaster clean-up (the Bangkok floods of 2011, the Southeast Asia tsunami of 2004, the Kobe earthquake, and Hurricane Katrina remediation projects).
EM has been employed in many agricultural applications, but is also used in the production of several health products in South Africa and the USA.
The concept of "friendly microorganisms" was developed by Professor Teruo Higa, from the University of the Ryukyus in Okinawa, Japan. He reported in the 1980s that a combination of approximately 80 different microorganisms is capable of positively influencing decomposing organic matter such that it reverts into a "life promoting" process. Higa invokes a "dominance principle" to explain the effects of his "Effective Microorganisms". He claims that three groups of microorganisms exist: "positive microorganisms" (regeneration), "negative microorganisms" (decomposition, degeneration), "opportunist microorganisms". In every medium (soil, water, air, the human intestine), the ratio of "positive" and "negative" microorganisms is critical, since the opportunist microorganisms follow the trend to regeneration or degeneration. Therefore, Higa believes that it is possible to positively influence the given media by supplementing with "positive" microorganisms.
The Effective Microorganisms (EM) concept is considered controversial in some quarters and there is no scientific evidence to support all of its proponents' claims. This is acknowledged by Higa in a 1994 paper co-authored by Higa and soil microbiologist James F Parr, a USDA Research, they conclude in that, "the main limitation...is the problem of reproducibility and lack of consistent results.".
Parr and Higa mention soil pH, shading, soil temperature and flooding as factors affecting the interaction of EM with local microbiological organisms, and with each other. The philosophical approach that Higa and Parr invoke is the maintaining of pH and soil temperature within conditions known to be detrimental to negative microorganisms as well as the addition of EM to favorably tip the balance of positive and negative microorganisms in favor of the positive microorganisms.
For these reasons the two proponents of the technology (Higa and Parr) dismiss "silver bullet" beneficial microorganism inoculants that are only a single microorganism (single strain/single genus) as generally ineffective due to the host of uncertainty about the conditions a single microorganism would be effective in. They cite the acknowledgment by the scientific community that multiple microorganisms (as in the case of Bokashi, invented and marketed by Higa) in coordination with good soil management practices positively influence soil microorganisms and plant growth and yield. They call for additional research to develop more information on soil microorganisms and their interactions.
Recently, peer reviewed research is coming out on the technology. Many of the claims are being put to the test. An example is a paper written by Myint Lwini and S. L. Ranamukhaarachchi. The paper discusses biological controls of bacterial wilt disease and showed that application of EM and EM Bokashi were most-effective as bio-control agents. Other articles, such as those by Yamada and Xu examine the use of EM in making organic fertilizers. Hui-Lian Xu has been researching Effective Microorganisms for several years. Some of his research has been on photosynthesis and yield of sweet corn, Physiological characteristics in peanuts, and fruit yield and quality of tomato plants. Others are also looking at pre-harvest  and post-harvest  applications of EM-1.
Many of the earlier peer reviewed papers were on EM-X Rice Bran Supplement, a product sold for human consumption. These papers include papers written by Chui, CH, Datla, KP, and Ke B. Most of this research was on the antioxidant effects, anti-inflammatory effects, and effects on various forms of cancers.
The use of EM in the bokashi intensive composting process for home kitchen waste has been in use in Christchurch, New Zealand for several years, backed by the local city council, and its use as a plant fertilizer is beginning to be researched locally.
- "Trademark Guidelines". emrojapan.com. 2011 [last update]. Retrieved November 13, 2011.
- Szymanski, N.; Patterson, R.A. (2003). "Effective Microorganisms (EM) and Wastewater Systems in Future Directions for On-site Systems: Best Management Practice." (PDF). In R.A. and Jones, M.J. (Eds). Proceedings of On-site '03 Conference. Armidale, NSW, Australia: Lanfax Laboratories. pp. 347–354. ISBN 0-9579438-1-4. Retrieved 2006-11-14.
- Higa, Dr. Teruo; Dr. James Parr (1994). "Beneficial and Effective Microorganisms for a Sustainable Agriculture and Environment." (PDF). Atami, Japan: International Nature Farming Research Center. p. 7. Retrieved 21 January 2008.
- MYINT LWIN1 AND S.L. RANAMUKHAARACHCHI. Development of Biological Control of Ralstonia solanacearum Through Antagonistic Microbial Populations. International Journal of Agriculture & Biology. 8(5), 2006. Pp 657–660.
- Yamada, K and Xu, H. Properties and Applications of an Organic Fertilizer Inoculated with Effective Microorganisms. Journal of Crop Production. 3(1) June 2001. Pp 255–268.
- Xu, Hui-Lian. Effects of a Microbial Inoculant and Organic Fertilizers on the Growth, Photosynthesis and Yield of Sweet Corn. Journal of Crop Production. 3(1). June 2001. Pp 183–214.
- Yan, P.S. and Xu, H.L. Influence of EM Bokashi on Nodulation, Physiological Characteristics and Yield of Peanuts in Nature Farming Fields. Journal of Sustainable Agriculture. Vol. 19, 2002. Pp 105–112.
- Xu, H.L.; Wang, R; Mridha, A.U. Effects of Organic Fertilizers and a Microbial Inoculant on Leaf Photosynthesis and Fruit Yield and Quality of Tomato Plants. Journal of Crop Production. 3(1) 2001. Pp 173–182.
- Daiss, N.; Lobo, M.G.; Socorro, A.R.; Bruckner, U.; Heller, J.; Gonzales, M. The effect of three organic pre-harvest treatments on Swiss Chard (Beta vulgaris. L var. cycla L.) quality. European Food Research and Technology. 226(3). Pp 345–353.
- Daiss, N; Lobo, M.G.; Gonzalez, M. Changes in Postharvest Quality of Swiss Chard Grown Using 3 Organic Preharvest Treatments. Journal of Food Science. 73(6), August 2008. Pp S314-S320.
- Chui CH, Hau DK, Lau FY, Cheng GY, Wong RS, Gambari R, Kok SH, Lai KB, Teo IT, Leung TW, Higa T, Ke B, Tang JC, Fong DW, Chan AS. Apoptotic potential of the concentrated effective microorganism fermentation extract on human cancer cells. International Journal of Molecular Medicine. 2006 Feb: 17(2): 279-84.
- Datla KP, Bennett RD, Zbarsky V, Ke B, Liang YF, Higa T, Bahorun T, Aruoma OI, Dexter DT. The antioxidant drink effective microorganism-X (EM-X) pre-treatment attenuates the loss of nigrostriatal dopaminergic neurons in 6-hydroxydopamine-lesion rat model of Parkinson's disease. Journal of Pharmacy and Pharmacology. 2004 May; 56(5): 649-54.
- Ke B; Xu Z; Ling, Y; Qiu, W; Xu, Y.; Higa, T; Aruoma, OI. Modulation of experimental osteoporosis in rats by the antioxidant beverage effective microorganisms-X (EM-X). Biomed Pharmacother 2009 Feb; 63(2): 114-9. Epub 2008. Apr 16.
Further reading 
- Amon B, Kryvoruchko V, et al.: Einfluss von "Effektiven Mikroorganismen" auf Ammoniak-, Lachgas- und Methanemissionen und auf das Geruchsemissionspotential während der Lagerung von Schweineflüssigmist und -festmist. Bericht der Universität für Bodenkultur Wien im Auftrag der Multikraft GmbH, 2004 PDF
- Faculty of Agriculture, University of Agriculture, Faisalabad
- Teruo Higa (1991)"Microorganisms for Agriculture and Environmental Preservation" Publishers site