Dynamics of Bacillus thuringiensis var. israelensis and Lysinibacillus sphaericus spores in urban catch basins after simultaneous application against mosquito larvae - PubMed (original) (raw)

Dynamics of Bacillus thuringiensis var. israelensis and Lysinibacillus sphaericus spores in urban catch basins after simultaneous application against mosquito larvae

Valeria Guidi et al. PLoS One. 2013.

Abstract

Bacillus thuringiensis var. israelensis (Bti) and Lysinibacillus sphaericus (Lsph) are extensively used in mosquito control programs. These biocides are the active ingredients of a commercial larvicide. Quantitative data on the fate of both Bti and Lsph applied together for the control of mosquitoes in urban drainage structures such as catch basins are lacking. We evaluated the dynamics and persistence of Bti and Lsph spores released through their concomitant application in urban catch basins in southern Switzerland. Detection and quantification of spores over time in water and sludge samples from catch basins were carried out using quantitative real-time PCR targeting both cry4A and cry4B toxin genes for Bti and the binA gene for Lsph. After treatment, Bti and Lsph spores attained concentrations of 3.76 (± 0.08) and 4.13 (± 0.09) log ml(-1) in water, then decreased progressively over time, reaching baseline values. For both Bti and Lsph, spore levels in the order of 10(5) g(-1) were observed in the bottom sludge two days after the treatment and remained constant for the whole test period (275 days). Indigenous Lsph strains were isolated from previously untreated catch basins. A selection of those was genotyped using pulsed field gel electrophoresis of SmaI-digested chromosomal DNA, revealing that a subset of isolates were members of the clonal population of strain 2362. No safety issues related to the use of this biopesticide in the environment have been observed during this study, because no significant increase in the number of spores was seen during the long observation period. The isolation of native Lysinibacillus sphaericus strains belonging to the same clonal population as strain 2362 from catch basins never treated with Lsph-based products indicates that the use of a combination of Bti and Lsph for the control of mosquitoes does not introduce non-indigenous microorganisms in this area.

PubMed Disclaimer

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1

Figure 1. Standard curves for the quantification of Lysinibacillus sphaericus (A) and Bacillus thuringiensis israelensis (B).

Each spore concentration was tested with 9 replicates on 3 different runs. Linear regressions, Lsph: y = 3.59x+40.71, R2 = 0.98; Bti: y = 3.39x+37.50, R2 = 0.97. The dashed line represents the LOQ of the real-time PCR assay.

Figure 2

Figure 2. Evolution of Lysinibacillus sphaericus and Bacillus thuringiensis israelensis spores in water and sludge samples collected in treated catch basins (average±SE).

Symbols: ○ = Lsph spores per ml of water; • = Bti spores per ml of water; □ = Lsph spores per gram of sludge; ▪ = Bti spores per gram of sludge.

Figure 3

Figure 3. PFGE patterns of _Sma_I digested genomic DNA of the 11 Lysinibacillus isolates and references (strains 2362 and the ATCC14577T).

Sb: Salmonella serotype Braenderup H9812 restricted with _Xba_I.

Figure 4

Figure 4. Neighbour-joining phylogenetic tree based on 16S rRNA gene sequences of isolates 4.1, 4.2, 9.3 and 11.5, as well as strain 2362 and some other strains belonging to related taxa.

The evolutionary distances are based on the Kimura 2-parameter model. Bootstrap values (>50%) based on 1000 replications are shown at branch nodes. Gene Bank accession numbers are given in parentheses. Paenibacillus polymyxa NCDO 1774T was used as outgroup. Phylogenetic analysis was performed using MEGA version 4.

References

    1. Ahmed I, Yokota A, Yamazoe A, Fujiwara T (2007) Proposal of Lysinibacillus boronitolerans gen. nov. sp. nov., and transfer of Bacillus fusiformis to Lysinibacillus fusiformis comb. nov. and Bacillus sphaericus to Lysinibacillus sphaericus comb. nov. Int J Syst Evol Microbiol 57: 1117–1125. -PubMed
    1. Poopathi S, Abidha S (2010) Mosquitocidal bacterial toxins (Bacillus sphaericus and Bacillus thuringiensis serovar israelensis): Mode of action, cytopathological effects and mechanism of resistance. J Physiol 1: 22–38.
    1. Lacey LA (2007) Bacillus thuringiensis serovariety israelensis and Bacillus sphaericus for mosquito control. J Am Mosq Control Assoc 23: 133–163. -PubMed
    1. Krych VK, Johnson JL, Yousten AA (1980) Deoxyribonucleic acid homologies among strains of Bacillus sphaericus . Int J Syst Bacteriol 30: 476–484.
    1. Priest FG (1992) Biological control of mosquitoes and other biting flies by Bacillus sphaericus and Bacillus thuringiensis . J Appl Microbiol 72: 357–369. -PubMed

MeSH terms

Substances

LinkOut - more resources