Abstract
BackgroundBacillus cereus 0–9, a Gram-positive, endospore-forming bacterium isolated from healthy wheat roots in our previous research, is considered to be an effective biocontrol strain against several soil-borne plant diseases. SpoVG, a regulator that is broadly conserved among many Gram-positive bacteria, may help this organism coordinate environmental growth and virulence to survive. This study aimed to explore the multiple functions of SpoVG in B. cereus 0–9.MethodsThe gene knockout strains were constructed by homologous recombination, and the sporulation process of B. cereus 0–9 and its mutants were observed by fluorescence staining method. We further determined the spore yields and biofilm formation abilities of test strains. Transcriptional fusion strains were constructed by overlapping PCR technique, and the promoter activity of the target gene was detected by measuring its fluorescence intensity. The biofilm production and colonial morphology of B. cereus 0–9 and its mutants were determined to study the functions of the target genes, and the transcription level of the target gene was determined by qRT-PCR.ResultsAccording to observation of the sporulation process of B. cereus 0–9 in germination medium, SpoVG is crucial for regulating sporulation stage V of B. cereus 0–9, which is identical to that of Bacillus subtilis but differs from that of Bacillus anthracis. In addition, SpoVG could influence biofilm formation of B. cereus 0–9. The transcription levels of two genes closely related to biofilm-formation, sipW and calY, were downregulated in a ΔspoVG mutant. The role of SpoVG in regulating biofilm formation was further explored by deleting the genes abrB and sinR in the ΔspoVG mutant, respectively, generating the double mutant strains ΔspoVGΔabrB and ΔspoVGΔsinR. The phenotypes of these double mutants were congruent with those of the single abrB and sinR deletion strains, respectively, which showed increased biofilm formation. This indicated that spoVG was located upstream of abrB and sinR in the regulatory pathway of B. cereus biofilm formation. Further, the results of qRT-PCR and the luminescence intensity of transcriptional fusion strains indicated that spoVG gene deletion could inhibit the transcription of Spo0A.ConclusionsSpoVG, an important regulator in the sporulation of B. cereus, is located upstream of Spo0A and participates in regulation of biofilm formation of B. cereus 0–9 through regulating the transcription level of spo0A. Sporulation and biofilm formation are crucial mechanisms by which bacteria respond to adverse conditions. SpoVG is therefore an important regulator of Spo0A and is crucial for both sporulation and biofilm formation of B. cereus 0–9. This study provides a new insight into the regulatory mechanism of environmental adaptation in bacteria and a foundation for future studies on biofilm formation of B. cereus.
Highlights
Bacteria have developed various mechanisms, some not yet known, to adapt and respond to adverse environmental factors during the long course of evolution
This study provides a new insight into the regulatory mechanism of environmental adaptation in bacteria and a foundation for future studies on biofilm formation of B. cereus
As a biocontrol bacterium derived from soil, B. cereus 0–9 has evolved various environmental adaptation mechanisms, such as swarming motility, biofilm formation, spore differentiation, etc
Summary
Bacteria have developed various mechanisms, some not yet known, to adapt and respond to adverse environmental factors during the long course of evolution. Biofilm formation and sporulation are two different effective survival strategies that enable bacteria to utilize a greater variety of nutrients, endure rapid environmental changes, and resist multiple adverse threats [1]. For Bacillus cereus, sporulation or biofilm formation is an effective self-protective behavior used to survive environmental pressures, such as nutrient deficiency, high temperature, high salt, antibiotics, etc. B. cereus produces a variety of biofilms that differ in their architecture and mechanism of formation, possibly reflecting an adaptation to various adverse environments [2]. The primary environmental signal for initiation of sporulation is nutrient limitation [6], which could induce characteristics of other adaptive responses, such as slow growth, non-proliferative stationaryphase cells, or biofilm formation. Bacillus cereus 0–9, a Gram-positive, endospore-forming bacterium isolated from healthy wheat roots in our previous research, is considered to be an effective biocontrol strain against several soil-borne plant diseases. This study aimed to explore the multiple functions of SpoVG in B. cereus 0–9
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