FlhF Is Required for Swarming Motility and Full Pathogenicity of Bacillus cereus

Abstract

Besides sporulation, Bacillus cereus can undergo a differentiation process in which short swimmer cells become elongated and hyperflagellated swarmer cells that favor migration of the bacterial community on a surface. The functionally enigmatic flagellar protein FlhF, which is the third paralog of the signal recognition particle (SRP) GTPases Ffh and FtsY, is required for swarming in many bacteria. Previous data showed that FlhF is involved in the control of the number and positioning of flagella in B. cereus. In this study, in silico analysis of B. cereus FlhF revealed that this protein presents conserved domains that are typical of SRPs in many organisms and a peculiar N-terminal basic domain. By proteomic analysis, a significant effect of FlhF depletion on the amount of secreted proteins was found with some proteins increased (e.g., B component of the non-hemolytic enterotoxin, cereolysin O, enolase) and others reduced (e.g., flagellin, L2 component of hemolysin BL, bacillolysin, sphingomyelinase, PC-PLC, PI-PLC, cytotoxin K) in the extracellular proteome of a ΔflhF mutant. Deprivation of FlhF also resulted in significant attenuation in the pathogenicity of this strain in an experimental model of infection in Galleria mellonella larvae. Our work highlights the multifunctional role of FlhF in B. cereus, being this protein involved in bacterial flagellation, swarming, protein secretion, and pathogenicity.

Enteropathogenic Potential of Bacillus thuringiensis Isolates from Soil, Animals, Food and Biopesticides

“…So far, all B. thuringiensis isolates in this study showed the genetic premises (presence of enterotoxin genes) to provoke the diarrhoeal type of food poisoning. Nevertheless, prerequisites for B. cereus enterotoxin production and cytotoxicity are also spore germination [ 14 , 40 , 41 , 42 , 43 ] and motility [ 14 , 44 , 45 , 46 ] in the host’s intestine.…”

“…In order to assess the potential health risk originating from (biopesticidal) B. thuringiensis isolates in more detail, we additionally investigated germination and motility behaviour of the strain set, which are further crucial prerequisites for the onset of the diarrhoeal disease [ 14 , 40 , 41 , 42 , 43 , 44 , 45 , 46 ]. Although different germination patterns emerged, spores of most isolates were able to germinate, even in cRPMI medium with preceding heat treatment mimicking re-heating of stored foods and subsequent consumption.…”

Consumed Foodstuffs Have a Crucial Impact on the Toxic Activity of Enteropathogenic Bacillus cereus

“…In routine diagnostics, the enteropathogenic potential of a new isolate is so far determined via its ability to produce enterotoxins after growth under standard laboratory conditions ( Jessberger et al, 2015 ). However, in the meantime B. cereus food infections are rather understood as multifactorial processes including various steps such as (i) the survival of spores during stomach passage ( Clavel et al, 2004 ; Wijnands et al, 2009 ; Ceuppens et al, 2012a ; Berthold-Pluta et al, 2015 ), (ii) germination of spores in the small intestine ( Clavel et al, 2004 ; Wijnands et al, 2006 , 2007 ),(iii) motility ( Ghelardi et al, 2007 ; Salvetti et al, 2007 ; Mazzantini et al, 2016 ), (iv) adhesion of spores and vegetative cells to the intestinal epithelium ( Minnaard et al, 2004 ; Ramarao and Lereclus, 2006 ), and afterward (v) the production of enterotoxins under intestinal conditions ( Jessberger et al, 2017 ). Furthermore, the impact of complex foodstuffs has also been tested, mainly focusing on bacterial survival.…”

Necrosignaling: Cell death triggers antibiotic survival pathways in bacterial swarms

“…Bacteria employ many appendages for movement and dispersal in their ecological niches 9 . Flagella-enabled swarming offers bacteria a competitive advantage in both ecological and clinical settings 10,11 . An unexpected and clinically relevant property of swarms is their SR at conditions lethal to free-swimming planktonic cells of the same species 2-5,12 .…”

“…S1a, b). At low concentrations (e.g, Kan 2.5 ; 2.5μg/ml), and during the early phase of growth (0.5 h), swarm cells were surprisingly more susceptible to killing than planktonic cells, a trend maintained for up to Kan 10 (Fig. S1a).…”