gcpA (stm1987) is critical for cellulose production and biofilm formation on polystyrene surface by Salmonella enterica serovar Weltevreden in both high and low nutrient medium
Authors: Patit Paban Bhowmick
Iddya Karunasagar
H A Darshanee Ruwandeepika
Thilo M Fuchs
Devananda Devegowda
Shabarinath Srikumar
Indrani Karunasagar
Journal: Microbial Pathogenesis (2011)
Discipline: IMMUNOLOGY
Keywords: Salmonella; biofilm formation; seafood isolates; Salmonella enterica serovar Weltevreden; nutrient conditions
Affiliations: Department of Fishery Microbiology, Karnataka Veterinary, Animal and Fisheries Sciences University, College of Fisheries, Mangalore, India.

Abstract:  Biofilm formation by Salmonella is a serious concern in the food-processing industry and the persistence of the organism in biofilms becomes a constant source of contamination. Since there is zero tolerance for Salmonella in foods, it is important to understand the mechanism of biofilm formation and to prevent the formation. Therefore, this study aimed at investigating the biofilm-forming ability of seafood isolates of Salmonella enterica serovar Weltevreden (S. Weltevreden) under two different nutrient conditions (normal strength trypticase soy broth (TSB) and 1:100 diluted TSB). The role of cellulose production in biofilm formation and in the expression of multicellular behavior (rough, dark, red morphotype: rdar) was investigated. Fourteen isolates of seafood associated S. Weltevreden were studied for biofilm production in polystyrene microtitre plates. Only one (SW49) of 14 was a strong biofilm former on polystyrene template and was able to produce biofilm in both undiluted TSB and 1:100 diluted TSB at 24h. All others produced moderate or weak biofilms which was higher in 1:100 diluted TSB compared to undiluted medium. All the isolates except one were positive by PCR for the three genes, gcpA (stm1987), adrA (yaiC) and csgD. Gene expression of gcpA, adrA and csgD was studied by real-time PCR with the one strong (SW49) and one representative weak (SW30) biofilm former. In SW49 at 24h of incubation, the expression of gcpA from biofilm cells was 33 and 36 times higher than from planktonic cells grown in TSB and diluted TSB respectively and at 72h the expression from biofilm cells was 57 and 61 times higher than that from planktonic cells. Quantification of gene expression did not reveal any significant difference in the expression of csgD and adrA gene. Deletion of gcpA in SW49 resulted in its inability to produce cellulose and consequent inability to bind calcoflour, inability to form rdar colony on Congo Red-agar plates and failure to produce biofilm on polystyrene substrate. The data indicated that, in case of S. Weltevreden, gcpA is critical for activating cellulose synthesis and biofilm formation both in undiluted and diluted TSB. The results of this study suggest the existence of an alternative biofilm regulatory pathway in S. Weltevreden. Role of adrA in cellulose production in nutrient rich medium is known but role of gepA in the above phenomenon is proved in this study. An understanding of the genes involved would help in looking at strategies of repression of the gene to control formation of biofilm. 

Retracted: No

PubPeer comments:
 The central argument of this paper is circular in the same way that appeals to projective geometric concepts and effects are circular in general when employed as explanatory concepts in visual perception (recently discussed here: https: psyarxiv.com n5mbf and with respect to the u201cheight in the visual field depth cueu201d here: https: psyarxiv.com ej796 ). Ooi et al do something fairly common, which is to confuse and conflate the actual structure of the physical environment with the structure of the perceived environment. As with their concepts they are careless with their words, and this creates confusion as to what they are claiming. One interpretation amounts to an impossibility; the other to a circularity. The text shifts continually from implying the one to implying the other. The article begins: u201cFigure 1a illustrates the relationship between the angular declination below the horizon (a) and the absolute distance (d) of an objecton the ground from the observer. Assuming that the observer s eyeheight (h) is known (11), the object distance can be determined by obtaining the angular declination below the horizon: d=h tan(a)(refs 2u00b14).u201d Those two opening sentences seem to indicate the adoption of the impossible option. Observers eyeheight is not known to their visual processes. First, I can t conceive of a possible avenue, and none has been proposed, by which eye height relative to some aspect of the physical environment could be independently ascertained - ascertained, that is, by means other than the visual processing of the proximal stimulation, which, as is well known, is indirect and fallible. Also, if eyeheight were known, directly knowable or involved in our perceptual processes, we would not be susceptible to depth illusions, including photos and movies. We would not be susceptible to the Ames room illusion (which involves a sloping floor that appears level). Our sense of depth relations would become confused every time we sat down, got in a car, on a bike, as we grow, etc. We would need to u201crecalibrateu201d constantly. Ooi et al proceed to show that distorting prisms alter our perception of the structure of our environment and that this affected distance judgments in a predictable way. But we know that our perception of the location and inclination of the ground plane, for example, simultaneously entails a sense of distance along that plane. Perception of both inclination and distance are products of one process, not two; one is not the cause of the other. So this finding in no way furthers the  eye height hypothesis. The authors then acknowledge mid-article that the putative success of their eyeheight hypothesis hinges on an untested assumption: u201cOur findings have confirmed the two [circular] predictions of the angular declination hypothesis. This hypothesis, however, hinges on the implicit assumption that the visual system uses the eye level as a reference for computing the angular declination of the object (Fig. 1a). But while this assumption is critical, it also lacks direct empirical support.u201d Again, the authors seem to be implying that eye height is an independently ascertainable, physically valid piece of data that may be used to assess angular declination etc. But again, eye height, the location orientation of the ground plane, distance of objects, are all mutually dependent parts of the same process deriving from the same total proximal stimulation (that has no depth) to produce the percept. To treat any one feature of this percept as a cause of other features is a logical error. Ooi et al s claimed u201cconfirmationu201d of their eye height assumption is, consequently, as circular as their angular declination distance correlation confirmation. Indeed, at various points, they clearly use the term u201ceye heightu201d to mean perceived eye height. u201cWe first measured the observer s eye level by having the observer instruct the experimenter to locate a red light at the observer s eyelevel from a viewing distance of 2.4 m...[under three conditions:] baseline, prism and after-effect.u201d It was found that: u201cthe eye level can be altered by prisms.u201d u201cWe next verified the possibility that prism adaptation affects the judgements of both distance and height, possibly stemming from a recalibration of the eye level.u201d Again, here we re not talking about actual eye level, which cannot be altered by prisms. But in this case the second sentence of the article, which I quoted above ( u201cAssuming that the observer s eyeheight (h) is known ...u201d) becomes irrelevant. They have not shown that u201ceye heightu201d is known u2013 in fact, they ve shown the opposite u2013 that it is subject to distortion. Earlier, Ooi et al had described their angular declination hypothesis as saying that  the visual system can access the information regarding the angular declination below the horizon for distance perception....u201d Here, it seems we re talking about true physical information. Anyway, to sum up: 1. The authors are constantly switching between making claims based on treating u201ceye heightu201d as a veridical assessment of the viewer s situation relative to the physical environment, and treating it as a perceptual state. 2. In the former case their claim is impossible and in the second circular. We might just as well have (invalidly) argued that the visual system uses object distance from the viewer to evaluate angular declination, or eye height. ,