Class: Gamma Proteobacteria
Description and Significance
In Greek, Pseudomonad literally means 'false unit', being derived from pseudo and monas (Applied, 2002). The term "monad" was used in the early history of microbiology to denote single-celled organisms (Applied, 2002).
Characteristics of Pseudomonas chloroaphis includes secretion of pyoverdin (picture to the right), or fluorescent (Tombolini, 1999). This fluorescent is generally a yellow-green pigment and comes out when the organism is attached to the desired plant species, within the hystol section of soil, under iron limiting conditions (Meyer, 2002). Emission of these pigments allow for easy detection, using siderophore typing (Meyer, 2002).
In addition, Pseudomonas chlororaphis is an effective biocontrol agent against Pythium aphanidermatum, a casual damping affect of hot pepper seedlings in greenhouse vegetable production, and this microorganism reduces and often eliminates soft-rot in leaves of the tobacco plant that is caused by Erwinia carotovora (European, 2009).
Many applications of Pseudomonas chlororaphis are in agriculture and horticulture by acting against various fungal plant pathogens by creating phenazine (antibiotic to root rot of cucumbers, peppers, tomatoes, and many other agricultural crops) (Woeng, 2000).
The genome of Pseudomonas chlororaphis has not been mapped at this current time.
Cell Structure, Metabolism and Life Cycle
Pseudomonas chlororaphis are rod-shaped, non-spore forming, gram-negative bacteria with one or more polar flagella (Todar, 2006). The microorganisms' flagella allow for motility (Asano et al, 1981).
The organism is typically an aerobic heterotroph, but has also been shown to perform denitrification within the rhizosphere of Glyceria maxima (Reed mannagrass). The end product of dentrification by P. chlororaphis tends to be N20 (Bodelier et al, 1997). Growth of P. chlororaphis is stimulated by the roots of G. maxima, not only in the direct rhizosphere, but also within the surrounding sediments (Bodelier and Laanbroek, 1997). It was also shown that P. chlororaphis competes with Nitrosomonas europaea for oxygen in the rhizosphere of plants, but competition is controlled by the oxidation kinetics of the electron donor ("instead of the oxygen uptake kinetics of the respective organisms." (Bodelier and Laanbroek, 1997)
As described above, The United States Environmental Protection Agency (EPA) states that some strains of P. chlororaphis act as effective fungicides when found in situ, as well as when used in soil inoculation. The bacteria can be applied directly to cereal seeds prior to sowing, which has been shown to act as an effective biocontrol agent in over 11 European countries (Tombolini et al, 1999). The organisms shield plant roots by producing antibiotics and by immobilizing iron that is needed for fungal growth (EPA, 2009). P. chlororaphis also produces cytokinin and other plant growth factors that help plants resist fungal infection (EPA, 2009). Efficacy of P. chlororaphis as an antifungal agent is dependent upon the characteristics of each strain, thus, several companies (such as Lantmännen BioAgri AB of Sweden) have performed extensive research comparing strains and method of inoculation (Tombolini et al, 1999).
Pseudomonas chlororaphis has also been used in industrial acrylamide production. Specific strains actively produce nitrile hydrases that hydrate nitriles to amides (Yamada and Kobayashi, 1996). This technique of enzymatic acrylamide production consumes 30% less energy and produces 7% less CO2 than conventional acrylamide production (includes steam, electric power, and raw materials; OECD, 2001). Common uses of acrylamide include adhesives, coagulants, paints, paper, and soil ammendments (Yamada and Kobayashi, 1996).
Ecology and Pathogenesis
Pseudomonas chlororaphis is a heterotrophic, soil bacteria that can be found in the rhizosphere, phyllosphere and surrounding sediments (Bodelier and Laanbroek, 1997; Legard et al. 1994). It is mesophilic with an ideal growth temperature range between 20°C-28°C (Selin et al., 2010; Palmfeldt et al., 2003; Bardas et al., 2009; Bodelier et al., 1997) and growth best around a pH of 6.3-7.5 (Rij ET, 2004; Bodelier and Laanbroek, 1997).
Pseudomonas chlororaphis has been observed to occupy the same site (the grooves along the junctions of epidermal cells) as Pseudomonas fluorescens when applied to tomato seedlings (Bloemberg et al., 2001); however, a clear symbiotic relationship has not been defined for P. chlororaphis. Additionally, many soil microorganisms are difficult to culture, and non-culturable microorganisms may account for a large part of the microflora, this does not take away the possibility of a symbiosis being discovered as non-culturable techniques improve, should be considered. biogeochemical significance.
Due to their ability to perform denitrification, P. chlororaphis have a biogeochemical significance of producing dinitrogen gas from nitrate (Palleroni et al., 2005)
Several strains of P. chlororaphis have been shown to be efficient root colonizers (Bloemberg et al., 2001); capable of producing a variety of antifungal substances including phenazine-1-carboxamide (PCN), hydrogen cyanide, chitinases and proteases (Bloemberg et al., 2001); The effectiveness of P. chlororaphis as a biocontrol agent has made it an organism of interest for agriculture (Selin et al., 2010, Khan et al., 2003).
Although P. chlororaphis is an effective biocontroller of certain fungi, it is generally considered a nonpathongenic bacterium. The Environmental Protection Agency states that,”Pseudomonas chlororaphis has shown no toxicity or pathogenicity to humans, wildlife, or the environment (EPA, 2009).” However, there have been limited reports of P. chlororaphis acting as a fish toxin (Hatai K, 1975).
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Page authored by Brad J. Wardynski, Michael Wandersee, and Erika White, students of Prof. Jay Lennon at Michigan State University.