Magnetic bacteria

First discovered in 1975 by Blakemore, the magnetotactic bacteria are bottomdwelling micro-organisms which are either anaerobic or microaerophilic [88]. It seems that the tendency of the bacteria to migrate downward along the component of the magnetic field is an evolutionary tactic that the anaerobic bacteria use to 

Note that the earth s magnetic field has a strength of the order of 1 G, see [88]. 

But what does all this have to do with corrosion and MIC There is some indirect and direct evidence here magnetotactic cells can accumulate iron approximately 20,000- to 40,000-fold over its extracellular concentration [118]. Between 14% and 79% by weight of the magnetosome is magnetite (Fe304), where the existence of. .. other oxides of iron or. .. iron sulphides in certain magnetotactic bacteria cannot be mled out [118]. If these bacteria need this much iron, from where can they get it  

Could magnetosome formation mechanisms contribute to corrosion in the way that iron-reducing bacteria do by consuming ferric iron ions While this is yet not known about magnetic bacteria, there is indirect evidence showing that the bacteria with magnetic properties could indeed be very important in MIC. 

Bahaj et al. were able to establish a way to explain, at least theoretically, how magnetic fields may be effective in encouraging biofilm formation and MIC. Ja-vaherdashti [119] proposed using magnetotactic bacteria to, literally, corral corrosion-enhancing bacteria at a suitable comer of a system and then expose them to MIC chemical (biocide application) or physical (filtration) mitigation methods. 

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Vali, H. Kirschvink, J.L. (1991) Observations of magnetosome organization, surface stmc-ture, and iron biomineralization of undescribed magnetic bacteria Evolutionary speculations. In Frankel, R.B. Blakemore, R.P. (eds.) Iron biominerals. Plenum Press, New York, 97-115... 

This chapter will deal with MIC, its definition and importance, and how historically both our understanding of and research methods for the study of MIC have evolved. We will then have a look at the parameters that can be used for categorising bacteria, and also the steps involved in biofilm formation. After discussing the ways by which biofilms can both accelerate and decelerate corrosion, we will look at three examples of bacteria that are involved in corrosion, the well-known SRB (sulphate-reducing bacteria), the rather shy , infamous IRB (iron-reducing bacteria) and almost unknown magnetic bacteria. 

Certainly, there are still many puzzles in dealing with magnetic bacteria. However, using these bacteria in mitigation programs may prove to be more efficient than other MIC control methods, if research in this very new and exotic area of MIC is supported in the manner it deserves. 

Sakaguchi T, Tsujimura N, Matsunaga T (1996) A novel method for isolation of magnetic bacteria without magnetic collection using magnetotaxis. J Microbiol Meth (26) 139-145... 

Javaherdashti R (1997) Magnetic bacteria against MIC. Paper No. 419, CORROSION 97, NACE International... 

Magnetic Bacteria May Remove Metals from Contaminated Soils (1997) Chemical News, Mater Perform 36(1) 47... 

A possible, yet stiU theoretical, use of magnetic bacteria (Chapter 4) could be using them in a system contaminated with, say, SRB to corral the SRB and, literally speaking, pushing them to a spot under the effect of a magnetic field and then apply biocide to them. See [57]. 

Selifonov SA, PJ Chapman, SB Akkerman, JE Gurst, JM Bortiatynski, MA Nanny, PG Hatcher (1998) Use of nuclear magnetic resonance to assess fossil fuel biodegradation fate of [l- C]acenaphthene in creosote polycyclic aromatic compound mixtures degraded by bacteria. Appl Environ Microbiol 64 1447-1453. 

When the bacteria to be detected are less than 1% of the total population in a sample, IFAs cannot be used because of interference from unrelated particles that are concentrated when large volumes of sample are filtered. To overcome this problem, the organism of interest may be concentrated by immunomagnetic separation.10,51 62 For this procedure magnetic beads coated with monoclonal or polyclonal antibodies are mixed with the sample. The beads are collected with a magnet, and the cells attached to the beads then are removed, enumerated, and identified by IFAs. 

DNA,83 which produces one million or more copies of amplified DNA in a short time. For identification of bacteria, PCR can be used to amplify DNA either after extraction from a sample or after lysis of the cells.83,84 Methods using washing, filtration, or magnetic beads with specific antibodies can be used to collect bacterial cells for PCR.85,86 PCR can be modified for the detection of bacteria from various sources32 and can even amplify DNA from dead cells.87... 

Comonomers, such as 3-hydroxyvalerate (3HV, ethylene R-unit (-CH2-CH3) in Fig. 1) and 4-hydroxybutyrate, have been incorporated in the PHB chains using specific additives in the growth medium of the bacteria [21-25]. It has been shown by nuclear magnetic resonance (NMR) studies that poly(3HB-co-3HV) has a statistically random distribution of the monomer units throughout a range of compositions varying from 0 to 90 mol % 3HV [23-26]. 

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