mentioned in any subsequent study. The emerging filament surrounded by a capsule Microbiology Comment provides a species was transferred to Leptothrix by Dorff (Fig. 1a). Subsequent growth is rapid with platform for readers of Microbiology to (5) in 1934, thus acquiring the name by which organisms approaching 100 µm in length in communicate their personal observations it has since been known. The late E. G. 2-d cultures (Fig. 1b). The organisms are and opinions in a more informal way than Mulder, the authority on sheathed iron bac- sometimes detached from their holdfasts (Fig. through the submission of papers. teria, grew L. discophora on agar media and, 1c), presumably due to the considerable shear- Most of us feel, from time to time, that with specially constructed apparatus, in run- ing forces generated when a coverslip is other authors have not acknowledged the ning ditch water (8). The wide capsular layer applied. The capsules, tinted brown with work of our own or other groups or have was observed on organisms from ditchwater ochre, disappear in a few minutes in 1% omitted to interpret important aspects of but not those from agar media. Holdfasts oxalic acid (a solvent for hydrated ferric their own data. Perhaps we have were not seen, and Mulder (7) concluded that oxide), but the sheaths, unlike those of observations that, although not sufficient within the genus holdfasts were confined to Leptothrix ochracea (3), are unaffected. In to merit a full paper, add a further Leptothrix lopholea. In 1986, Adams & 7-d cultures, few organisms remain attached dimension to one published by others. In Ghiorse (1) showed that L. discophora loses to their holdfasts, which continue to adhere to other instances we may have a useful piece the ability to form sheaths in culture. In 1992, the substratum. These mature holdfasts (Fig. of methodology that we would like to Emerson & Ghiorse (6) found cultural con- 1d) are darker than the capsule, presumably share. ditions that permitted the retention of the due to manganese deposition – L. discophora sheath and a rather limited development of has enzymes capable of iron and manganese The Editors hope that readers will take full the capsular layer, but in neither study were oxidation (4). The holdfasts have a central advantage of this section and use it to raise holdfasts seen. L. discophora has hence be- pore, corresponding in diameter to the sheath, matters that hitherto have been confined to come the disc-bearing Leptothrix that lacks and a concentric pattern of differing degrees a limited audience. discs. of darkening, perhaps a consequence of vari- Christopher M. Thomas, Editor-in-chief We have observed L. discophora in crude ations in the availability of manganese. culture during a study of an iron-rich water- Our observations confirm those of Schwers course in Berkshire (2). Samples were taken (9), who first described the species. The from the stream and nearby ditches where it question arises as to why holdfasts have not enters the Silwood wetland (Ordnance Survey been observed by other microbiologists who The discs of Leptothrix grid reference SU 940690), and consisted of have studied L. discophora. One possibility is discophora: lost for 89 stream water, anaerobic mud, and an over- that holdfasts, like capsules and sheaths (1), years? lying aerobic layer rich in ochre. They were are lost in culture. In addition, holdfasts are placed in loosely capped jars in the laboratory. probably initiated when a motile cell arrives The filamentous sheathed bacterium Lepto- When the mud had settled and the water had at a substratum, and so are unlikely to occur thrix discophora was described in 1912 by become clear, microscope slides were inserted Schwers (9), although he named it Megalo- so that the slide was exposed to anaerobic M GUIDELINES thrix discophora. He examined 1600 sediment mud, the intermediate zone where oxygen and Communications should be in the form samples from iron- and manganese-rich seep- ferrous iron both occur, and the supernatant of letters and should be brief and to the ages, springs and wells from sites in Europe water. At intervals from a day to a week, a point. A single small Table or Figure may and Africa and found the species to be slide was removed, wiped on one side and be included, as may a limited number of widespread and abundant. His photomicro- partially drained, and a large coverslip placed references (cited in the text by numbers, graphs show filaments about 1 µm wide and on the other side. Microscopy showed that and listed in alphabetical order at the end up to 100 µm long with sharply defined the iron bacteria, especially L. discophora of the letter). A short title (fewer than 50 sheaths, within which are a line of cells. The with its wide capsular layer, were abundant in characters) should be provided. filament is surrounded by a wide, diffuse the area of the slide corresponding to the mud capsular layer impregnated with ochre (hydra- surface. Occasionally, L. lopholea, the ac- Approval for the publication rests with ted ferric oxide). Sometimes at one end of the cepted holdfast-producing Leptothrix, was the Editor-in-Chief, who reserves the organism there is a basal disc or holdfast, seen, but was readily distinguished from L. right to edit letters and\or to make a which can be up to 10 µm wide. The capsular discophora by the absence of a capsular layer. brief reply. Other interested persons may layer tapers from the same width as the The development of L. lopholea is initiated also be invited to reply. The Editors of holdfast to disappear completely at the far when a motile cell contacts a solid object and Microbiology do not necessarily agree end of the filament. Discs detached from the becomes attached, probably by excreting a with the views expressed in filament are also shown. Schwers gave the sticky substance that hardens to initiate the Microbiology Comment. organism the epithet discophora (disc-bear- holdfast (8). This is likely to be true also for L. Contributions should be addressed to the ing) because of the frequent occurrence of discophora, but the earliest stage that we Editor-in-Chief via the Editorial Office. holdfasts. These holdfasts have not been observed consisted of a disc with a short Microbiology 147, June 2001 1393 Microbiology Comment pure culture may require freshly isolated material and the provision of surfaces that can be removed for examination. Two general points of interest emerge from the above: that very old reports may still be of value, and that supplementing pure cultures by observations in which natural (a) (d) conditions are simulated can be rewarding. Michael J. Carlile1† and A. William L. Dudeney2 1Department of Biology, Imperial College, Silwood Park, Ascot SL5 7PU, UK 2T. H. Huxley School of Environment, Earth Science and Engineering, Imperial College, London SW7 2BP, UK (b) †Present address: 42, Durleigh Road, Bridgwater TA6 7HU Author for correspondence: A. William L. Dudeney. Tel: j44 20 7594 7332. Fax: j44 20 7594 7444. e-mail: a.dudeney!ic.ac.uk 1. Adams, L. F. & Ghiorse, W. C. (1986). Physiology and ultrastructure of Leptothrix discophora SS-1. Arch Microbiol 145, 126–153. 2. Carlile, M. J. & Dudeney, A. W. L. (2000). Iron transport and retention in ochre-rich watercourses. Miner Resour Eng 9, 357–375. 3. Carlile, M. J. & Dudeney, A. W. L. (2000). A (c) microbial mat composed of iron bacteria. Microbiology 146, 2092–2093. 4. De Vrind-de Jong, E. W., Corsteigns, P. L. A. M., Fig. 1. Photomicrographs of L. discophora. Photography presents considerable problems, since features Kempers, E. S., Westbroek, P. & De Vrind, J. P. M. are not all in the same plane of focus, and ochre deposits in the capsule obscure details. (a–c) Two-day (1990). Oxidation of manganeses and iron by Leptothrix cultures, (d) 7-d culture. (a) A recently established organism. The filament, surrounded by a capsule, discophora: use of N,N,Nh,Nh-tetramethyl-p- has grown to the left from the initial point of attachment, now surrounded by an incipient disc. (b) An phenylaminediamine as an indicator of metal oxidation. older, attached organism, growing from a larger and darker disc at the right of the field. The filament Appl Environ Microbiol 56, 3458–3462. can be distinguished within the capsule for a short distance to the left of the disc. (c) A detached 5. Dorff, P. (1934). Die Eisenorganismen. Pflanzenforschung 16, 1–62. organism of similar age. The filament, being approximately in the same plane of focus throughout its 6. Emerson, D. & Ghiorse, W. C. (1992). Isolation, length, can be seen within the capsule. (d) A disc from which the filament, probably well over 100 µm cultural maintenance, and taxonomy of a sheath-forming long, has become detached. The central clear area of approximately 1 µm diameter, a feature of mature strain of Leptothrix discophora and characterisation of discs, corresponds in width to the central filament and marks its point of attachment to the surface. manganese-oxidizing activity associated with the sheath. The concentric pattern of differing degrees of darkening is usual in older discs. The base of the capsule Appl Environ Microbiol 58, 4001–4010. in old, detached filaments also commonly shows blackening. Bar, 20 µm (applies to entire figure). 7. Mulder, E. G. (1989). Genus Leptothrix.InBergey’s Manual of Systematic Bacteriology, vol. 3, pp. 1998–2003. Edited by J. T. Staley, M. P. Bryant, N. Pfennig, & J. G. Holt. Bailtimore: Williams & Wilkins. 8. Mulder, E. G. & Dienema, M. H. (1992). The in the agar cultures used in many studies. Our holdfasts are likely to remain attached to sheathed bacteria.