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Preliminary investigations on the effect of spore chain persistence on inoculum potential of Streptoverticillium strains R.W.ATTWELL and A. SURREY Department of Biological Sciences, Manchester Polytechnic, Manchester M1 5GD, UK
Code Number: AC91002
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Graphics: No associated graphics filesAbstract. The low numbers of Streptoverticillium isolates recovered from natural substrates may be due, in part, to the tendency of their spore chains to remain intact thereby reducing the inoculum potential. The need for an effective isolation system for members of the genus Streptoverticillium is well known (Attwell et al., 1985; Cardinali and Firrao, 1990). Such a system would facilitate industrial exploitation and an unbiased re- view of the taxonomy of the genus.
Similarities between Streptoverticillium and Streptomyces strains make elimination of the latter, from systems designed to isolate streptoverticillia, a major problem. Workers have attempted to discover characteristics which could be used to differentiate between the two genera in isolation procedures (Attwell et al., 1985; Hanka et al., 1985). An example is the difference between the gen- era in their sensitivity to lysozyme in liquid culture (Attwell et al., 1985) and on solid media (Cardinali and Firrao, 1990). But an isolation system which exploits the obvious selective potential of this enzyme has yet to be developed.
A second problem is the small numbers of Streptoverticillium colonies generally encountered on isolation media. This paper reports preliminary findings on the inoculum potential of Streptoverticillium spores, which may have a bearing on the low frequency of isolation. Materials and methods The Streptoverticillium and Streptomyces strains used are listed in Table 1. Spores were obtained from cultures grown on ISP2 medium for 14 days at 28 C. They were dislodged from the culture surface by means of a glass spreader and suspended into 0.01% Triton 100 solution.
Spore suspensions were examined microscopically to determine the numbers of spore chains and the chain lengths in each suspension. Enumeration was achieved by means of standard microscopic counting procedures.
Spore suspensions of Streptoverticillium aureoversales were subjected to sonication at 20Kc/second for periods ranging from 1 to 8 minutes and then examined microscopically.
Results and discussion The inoculum potential of each suspension is expressed as a % of the theoretical maximum value, in Tables 1 and 2. The theoretical maximum is the total number of spores present, assuming that each spore is one colony forming unit (CFU). The real inoculum potential is less than this value because many spores are aggregated into chains, or chain fragments, which constitute only one CFU irrespective of the number of spores they contain.
The tendency of spore chains of Streptoverticillium strains to remain intact in conditions where those of Streptomyces strains disintegrated was noticed during studies involving a wide range of members of both genera. It was more closely examined in the organisms listed in Table 1. The difference in inoculum potential between members of the two genera (Table 1) was significant (P<0.5) and a consequence of the persistence of the spore chain in Strepto- verticillium. It may also reflect differences in the spore sheath of these genera (Cross et al., 1973).
-------------------------------------------------------------- Species Strain Inoculum Potential (%) -------------------------------------------------------------- Streptoverticillium baldaccii ATCC 23654 20 Stv.olivoreti culi IPV 2252 32 Stv. biverticillatum ATCC 23615 36 Stv.aureoversales IPV 2051 39 Streptomyces fradiae ATCC 10745 74 Stm.diastaticus ATCC 3315 80 Strn.griseus ATCC 23345 89 Stm.viridochromogenes NCIB 9597 93 --------------------------------------------------------------Table 1. The inoculum potential of spore suspensions of representative Streptoverticillium and Streptomyces strains expressed as a % of the theoretical maximum (ATCC= American Type Culture Collection, Maryland, USA; IPV= Istituto di Patologia Vegetale, Milan, Italy; NCIB= National Collection of Industrial Bacteria, Aberdeen, UK). -------------------------------------------------------------- The possibility of persistence of the Streptoverticillium spore chain in environments such as soil requires further investigation since it may depress recovery levels. If this does prove to be a problem it could be counteracted by ap- plication of treatments, such as sonication (Table 2), which break up chains thereby increasing inoculum potential.
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Sonication Period (minutes) Inoculum Potential (%)
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0 39
1 45
2 51
4 54
8 53
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Table 2. The inoculum potential of spore suspensions of
Streptoverticillium aureoversales, expressed as a % of
the theoretical maximum, following various periods of
sonication.
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We do not claim to have devised an improved isolation
procedure for Streptoverticillium. However the char-
acteristic reported here, if taken together with other
distinctive features (Attwell et al.,1985; Hanka and
Schaadt 1988) of the genus, may form the basis of a successful
isolation system for these intriguing actinomycetes. |
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