Unit 2: Isolation and Characterization of Biopesticides - Practice Quiz

1 Which environmental sample is commonly collected to isolate beneficial microorganisms associated with plant roots?

2 What is the phyllosphere?

3 Which sample is especially useful for isolating fungi that infect insect pests?

4 What is the main purpose of serial dilution during microbial isolation?

5 Which technique spreads a measured volume of diluted sample over the surface of solid agar?

6 What is the purpose of a selective culture medium?

7 Why are aseptic techniques used during microbial isolation?

8 What does the term pure culture mean?

9 Which method is commonly used to obtain isolated bacterial colonies from a mixed culture?

10 Which feature is part of colony morphology?

11 Which instrument is used to observe the shape of microbial cells or fungal structures?

12 Gram staining is mainly used for the basic characterization of which group?

13 Which stain is commonly used to observe fungal hyphae and spores?

14 Which bacterial feature helps some Bacillus species survive unfavorable environmental conditions?

15 Which gene is commonly analyzed for molecular identification of bacteria?

16 Which DNA region is commonly used for molecular identification of fungi?

17 What is the main purpose of a bioassay when characterizing a potential biopesticide?

18 Why is an untreated control included in a biopesticide bioassay?

19 What does CFU stand for in microbial counting?

20 Why should environmental samples be collected in sterile containers?

21 Which sampling method is most appropriate for isolating microorganisms closely associated with the rhizosphere of a healthy plant?

22 A researcher wants to isolate epiphytic biocontrol bacteria from leaf surfaces without recovering many internal endophytes. Which method is most suitable?

23 Compost is being screened for thermotolerant antagonistic microorganisms. Which isolation condition would most directly favor their recovery?

24 A soil suspension is heated at for 10 minutes before plating. This treatment is most useful when isolating which potential biopesticide?

25 Which pretreatment is commonly used to improve the recovery of actinomycetes from soil containing many rapidly growing bacteria?

26 Soil is baited with susceptible insect larvae, and several larvae later die with fungal growth emerging from their bodies. What should be done next to isolate a likely entomopathogenic fungus?

27 A diseased caterpillar is suspected of containing a baculovirus. Which observation would best support this preliminary diagnosis?

28 A researcher plates mL of a soil dilution and counts 48 colonies. What is the estimated population in the original sample?

29 A bacterial colony selected from a soil dilution plate shows two colony types after transfer. Which procedure is best for obtaining a pure culture?

30 In a dual-culture assay, a pathogen grows 60 mm in the control and 24 mm toward an antagonist. What is the percentage inhibition of radial growth?

31 Which experimental setup best tests whether an isolate suppresses a fungal pathogen through volatile compounds?

32 A bacterial isolate produces an orange halo on chrome azurol S agar. Which biocontrol trait does this result indicate?

33 An isolate forms a clear zone around its colony on agar containing colloidal chitin. Which mechanism is most strongly supported?

34 Which marker combination is most appropriate for preliminary molecular identification of bacterial and fungal biopesticide isolates, respectively?

35 Two antagonistic bacterial isolates have identical 16S rRNA sequences but differ substantially in biocontrol activity. Which approach would best distinguish them genetically?

36 Rhizosphere samples must be transported for several hours before microbial isolation. Which practice best preserves the original culturable community?

37 A candidate antagonist reduces disease in detached leaves. Which treatment is essential for determining whether the reduction is caused by the antagonist rather than the application procedure?

38 A microorganism is being isolated from saline coastal soil for use against a root pathogen in the same environment. Which medium is most appropriate during initial screening?

39 A bacterial isolate creates a clear inhibition zone against a pathogen. How can a researcher help distinguish bactericidal activity from temporary growth inhibition?

40 After a promising isolate has been purified and characterized, which storage method best supports long-term preservation with minimal genetic change?

41 A researcher homogenizes 10 g of rhizosphere soil in 90 mL sterile diluent. After a further dilution of this homogenate, plating 0.1 mL produces a mean of 86 colonies. Assuming complete recovery and no clumping, what was the population density in the original soil?

42 Soil suspensions are heated at for 10 minutes before plating to isolate potential Bacillus biopesticides. Which interpretation of the resulting colonies is most defensible?

43 An antibiotic-containing enrichment broth yields the same antagonistic bacterium from 18 of 20 compost samples. Which conclusion is invalid without direct quantitative analysis of the original samples?

44 A bacterial isolate suppresses a fungal pathogen in a dual-culture agar assay but fails to protect plants in sterile potting mix. Which follow-up experiment best tests whether failure results from poor rhizosphere competence rather than loss of antifungal activity?

45 Insect-baiting of soil recovers Metarhizium frequently but no Beauveria, although metabarcoding detects both genera. What is the best explanation?

46 A bacterium is isolated after surface sterilization and maceration of healthy leaves. Which evidence most strongly supports its classification as an endophyte rather than a surface contaminant?

47 Two bacterial isolates with different pathogen-suppression spectra have identical full-length 16S rRNA gene sequences. Which approach is most appropriate for determining whether they are distinct strains and identifying candidate biocontrol traits?

48 Direct ITS sequencing of a presumptive fungal biopesticide produces reproducible overlapping peaks beginning at several positions. Microscopy also reveals two conidial morphologies. What should be done first?

49 A bacterial culture causes a strong color change in a chrome azurol S siderophore assay, but it also lowers the medium from pH 7.0 to pH 3.8. Which validation most directly addresses a potential false-positive result?

50 Cell-free culture filtrate inhibits a pathogen, but inhibition disappears after the filtrate is adjusted from pH 4.0 to pH 7.0. Which conclusion is best supported?

51 Which assay design best demonstrates that an isolate inhibits a fungal pathogen through volatile compounds rather than diffusible metabolites?

52 A wild bacterial isolate suppresses damping-off, whereas a mutant disrupted in a candidate antibiotic gene does not. Which additional result most strongly supports a causal role for that gene?

53 After application to leaves, strain-specific qPCR indicates target copies per gram for four weeks, but plate counts fall below detection after one week. Which method combination best distinguishes viable but nonculturable cells from persistent extracellular or dead-cell DNA?

54 An antagonistic fungal isolate progressively loses sporulation and disease suppression during repeated transfer on nutrient-rich agar. Which preservation strategy best minimizes further phenotypic drift?

55 A root-associated isolate shows excellent disease suppression and is identified as a member of a bacterial group containing opportunistic human pathogens. What is the most appropriate next characterization step before development?

56 Metagenomic analysis predicts abundant nonribosomal peptide biosynthesis genes in disease-suppressive soil, yet routine nutrient agar yields no isolates carrying them. Which isolation strategy is most rational?

57 A rare biocontrol bacterium is randomly distributed so that each enrichment well receives an average of 0.2 viable cells. Under a Poisson model, what is the probability that a well receives at least one viable cell?

58 Occlusion bodies resembling a baculovirus are recovered from diseased insect larvae. Why is propagation on cell-free bacteriological medium an unsuitable test of viability?

59 A Trichoderma isolate is assigned to a species from conidial morphology, but multilocus sequencing places it in a different cryptic species with distinct metabolite and safety profiles. Which identification should guide characterization?

60 A candidate bacterium reduces disease only when applied at very high density in low-nutrient substrate. Which experiment best separates nutrient competition from direct antibiosis as the principal mechanism?