LAB REPORT- PHENOTYPIC DIVERSITY AMONG SOILBORNE STREPTOMYCETES

Lab Report- Phenotypic Diversity Among Soilborne Streptomycetes



Lab Report- Phenotypic Diversity Among Soilborne Streptomycetes

Question 1

In this study, isolation of streptomycetes were done as well as inhibition assays. Four streptomycete isolates were found in soil sample and assayed against each isolate and with other organism, namely E. coli, P. flourescens, M. luteus, and B. subtilis. Total CFU g-1 in soil sample was found to be 2,160,000. Additional nutrients are added by having the oatmeal agar resulting to artificially high streptomycetes cfu count. Another methos used was serial dilution which can be used to quantify the number of streptomycetes in soils. Such approaches of quantifying and isolation Streptomycetes from soil were also done by other research groups. Figures 1-4 shows the inhibition rates of each organism. Streptomycete 1 showed no inhibition on Streptomycete 4, E. coli, and P. flourescens while Strep. 2 have inhibitions only on Strep. 3, and B. subtilis. Strep. 4 with same number of inhibitions with Strep. 2, inhibited Strep. 1, 3 and E. coli. Strep. 3 showed the lowest number of inhibited organism, only E. coli. Tables 1-2 show the size of the zone of inhibition with antibiotics.

Fig. 1. Pathogen antagonism by Streptomyces isolates from virgin prairie meadow and never tilled no-till monoculture plots, based on average values by block. (A) The proportion of isolates showing inhibitory activity against each of four plant pathogens. (B) The intensity of inhibition (measured as inhibition zone size) against each of four plant pathogens. Values shown are means and standard errors. No significant differences were found between treatments (p > 0.1, by t-test). 

Question 2

A majority of isolates showed inhibitory activity; 64% of isolates inhibited at least one of the four plant pathogens tested. Among our isolates, the frequency of inhibition against Fusarium, Rhizoctonia, Verticillium, and Streptomyces was 0.24, 0.40, 0.40, and 0.39, respectively. When all isolates were considered, antagonistic activity, including measures of both frequency and intensity, did not differ significantly by isolate origin (monoculture vs. prairie plant communities; Fig. 1).

Question 3

The inhibition assay was able to distinguish among 16 different inhibitory phenotypes. All but 3 ('Frvs', 'FrvS', and 'FRvS') of the 16 possible phenotypes were observed. The most frequently observed phenotypes were 'frvs' (36% of isolates), 'frvS' (13% of isolates), and 'FRVS' (11% of isolates). The distribution of isolates among the phenotypic groups differed slightly between treatments (Fig. 2). A significantly higher proportion of the monoculture isolates showed no inhibitory activity compared to the prairie isolates (phenotype 'frvs'; t = 2.98, p = 0.04). There was a trend toward a higher proportion of prairie isolates inhibiting Streptomyces only compared to monoculture isolates (phenotype 'frvS'; t = -2.53, p = 0.06). Intensity of inhibition within phenotypes differed only in one case; among isolates with the 'fRVS' phenotype, intensity of inhibition against Streptomyces was significantly greater for prairie isolates than for monoculture isolates (t = -3.54, p = 0.02). Intensity of inhibition did not differ between the two treatments for any of the other phenotypes (data not shown).

Fig. 2. Pathogen-inhibitory phenotypes of a Streptomyces isolate collection from diverse prairie (left) and from monoculture (right) plant communities, based on in vitro inhibition of four test pathogens. Each letter of the phenotype label corresponds to one of the four ...