Pink-Pigmented Facultative Methylotrophs

Pink-Pigmented Facultative Methylotrophs, commonly abbreviated to PPFMs, are bacteria that are members of the genus Methylobacterium and are commonly found in soil, dust, various fresh water supplies and on plant surfaces.[1] Although Gram negative, Methylobacteria often stain gram variable and are easily isolated using methanol-based mineral medium.[2] Their pigmentation, which is frequently pink but may also be yellow or orange, is thought to provide protection from solar UV radiation which damages the DNA of bacteria at low doses because of their small cell size. This color is present due to the carotenoid pigments within the cell.[3]

Metabolism

The metabolism of PPFMs is unusual because, as their name suggests, they are able to utilize C1 compounds such as formaldehyde, methanol and methylamine.[4] PPFM bacteria can undergo methylotrophy, a process in which the bacteria oxidize methanol with the help of the enzymes methanol dehydrogenase (MDH) and pyrroloquinoline quinone (PQQ)-linked protein.[3] In dense and diverse communities like those found in the phyllosphere and rhizosphere, this enables them to utilize nutrients other bacteria cannot, enhancing their competitive ability. In certain environments there are limited concentrations of elements such as carbon and phosphate in a usable form. Research suggests that PPFMs breakdown unusable forms of carbon into usable forms for other species forming symbiotic relationships.

Symbiosis with plants

PPFM bacteria form symbiotic relationships with numerous species of plants. PPFMs are horizontally transmitted to the next generation of plants through their seeds.[5] This relationship is beneficial for plants, as the PPFMs produce cytokines.[6] Plants with more growth showed an increased concentration in cytokine production, but credit has yet to be given to the bacteria.[5] It has also been established that PPFM symbionts produce additional growth factors such as ethylene,[7] auxins,[8] and gibberellic acid[9] which benefit the plants. This relationship is a model for plant-microbe interactions. As mentioned, PPFMs are known for their ability to utilize methanol as a sole energy source. It has been reported that trees and crop species emit large amounts of the alcohol methanol from their stomata, which potentially attracts symbiotic species. Interestingly, younger trees emit even more methanol which may encourage a healthy population of PPFM from an early stage of growth. Methanol breakdown by PPFMs allows plants to grow in different niches. Without this process, plants would not have access to enough carbon to grow efficiently. Studies also indicate that PPFM can break down additional carbon sources and also utilize phosphate efficiently,[3] potentially providing additional assistance to plants.

Overall, research in this field suggests that a plant's growth, survival, and reproductive success are significantly better when grown symbiotically with PPFMs. So far this relationship is only beneficial to haploid gametophytes, such as liverworts and mosses, but additional relationships are being investigated. There is a global application to this research, implying that PPFMs would be appropriate probiotic for some species of plants. Research by Mark Holland suggests that the normal storage of seeds for market use (after drying in a 50°C oven for 48h) rids the seeds of their native PPFM species. Incubating seeds with PPFM prior to germination encouraged germination and growth compared to controls.[5] Research suggests that this relationship extends to marine and freshwater plant species as well.[5] Additional research in this field will allow scientists to understand the complicated, yet important, relationship between plants and bacteria. PPFMs offer a low-cost biotech application to encourage enhanced growth, reproduction, and preferred characteristics of plant species in numerous environments.

See also

• Phyllosphere
• Rhizosphere

References

1. Omer ZS, Tombolini R, Gerhardson B (March 2004). "Plant colonization by pink-pigmented facultative methylotrophic bacteria (PPFMs)". FEMS Microbiology Ecology. 47 (3): 319–26. doi:10.1016/S0168-6496(04)00003-0. PMID 19712320.
2. Green PN (2001). "Methylobacterium". In Dworkin M (ed.). The Prokaryotes: An Evolving Electronic Resource for the Microbiological Community (3rd, release 3.7 ed.). New York: Springer-Verlag.
3. Kutschera U (March 2007). "Plant-associated methylobacteria as co-evolved phytosymbionts: a hypothesis". Plant Signaling & Behavior. 2 (2): 74–8. doi:10.4161/psb.2.2.4073. PMC 2633902. PMID 19516971.
4. Balachandar D, Raja P, Sundaram S (January 2008). "Genetic and metabolic diversity of pink-pigmented facultative methylotrophs in phyllosphere of tropical plants". Brazilian Journal of Microbiology. 39 (1): 68–73. doi:10.1590/s1517-83822008000100017. PMC 3768351. PMID 24031182.
5. Holland MA (April 2016). "Probiotics for Plants? What the PPFMs told us and some ideas about how to use them". Journal of the Washington Academy of Sciences. Washington Academy of Sciences. 102 (1): 31. ProQuest 1835329526.
6. Koenig RL, Morris RO, Polacco JC (April 2002). "tRNA is the source of low-level trans-zeatin production in Methylobacterium spp". Journal of Bacteriology. 184 (7): 1832–42. doi:10.1128/JB.184.7.1832-1842.2002. PMC 134930. PMID 11889088.
7. Madhaiyan M, Poonguzhali S, Senthilkumar M, Seshadri S, Chung H, Jinchul YA, Sundaram S, Tongmin SA (October 2004). "Growth promotion and induction of systemic resistance in rice cultivar Co-47 (Oryza sativa L.) by Methylobacterium spp. Botanical". Bulletin of Academia Sinica: 45.
8. Doronina NV, Ivanova EG, Trotsenko I (2002). "[New evidence for the ability of methylobacteria and methanotrophs to synthesize auxins]". Mikrobiologiia (in Russian). 71 (1): 130–2. PMID 11910802.
9. Siddikee M, Hamayun M, Han GH, Sa TM (2010). "Optimization of gibberellic acid production by Methylobacterium oryzae CBMB20". Korean Journal of Soil Science and Fertilizer. 43 (4): 522–7.