Divergent Influence to a Pathogen Invader by Resident Bacteria
with Different Social Interactions
Received: 19 December 2017 /Accepted: 16 May 2018
Springer Science+Business Media, LLC, part of Springer Nature 2018
Bacterial social interaction is a potential influencing factor in determining the fate of invading pathogens in diverse environments.
In this study, interactions between two representative resident species (Bacillus subtilis and Pseudomonas putida) and a leading
food-borne disease causative pathogen (Vibrio parahaemolyticus) were examined. An antagonistic effect toward V.
parahaemolyticus was observed for B. subtilis but not for P. putida. However, the relative richness of the pathogen remained
rather high in B. subtilis co-cultures and was, unexpectedly, not sensitive to the initial inoculation ratios. Furthermore, two
approaches were found to be efficient at modulating the relative richness of the pathogen. (1) The addition of trace glycerol
and manganese to Luria-Bertani medium (LBGM) reduced the richness of V. parahaemolyticus in the co-culture with B. subtilis
and in contrast, increased its richness in the co-culture with P. putida, although it did not affect the growth of V. parahaemolyticus
by its own. (2) The relative richness of V. parahaemolyticus on semisolid medium decreased significantly as a function of an agar
gradient, ranging from 0 to 2%. Furthermore, we explored the molecular basis of bacterial interaction through transcriptomic
analysis. In summary, we investigated the interactions between a pathogen invader and two resident bacteria species, showing
that the different influences on a pathogen by different types of interactions can be modulated by chemicals and medium fluidity.
In many natural environments and human infections, micro-
organisms live in dense communities termed biofilms [1–3].
As multiple species frequently exist together in a single bio-
film, the cells interact intimately. It is becoming increasingly
evident that interspecies interactions, or social interactions, are
essential for the persistence of species and the development of
microbial communities [4–6].
Interspecies interactions can either improve fitness or cause
species to compete for space and nutrients, leading to different
effects. For example, interspecies competition increases the
virulence of pathogens in two-species polymicrobial infec-
tions [6, 7]. Moreover, specific interactions between resident
commensal species and invading pathogens commonly mod-
ulate disease outcome. Species within human gut microbiota
can secret low molecular weight factors that repress the ex-
pression of virulence genes and inhibit the production of toxic
protein by enterohemorrhagic Escherichia coli (EHEC) .
Conversely, a predominant member of the human gut micro-
biota, Bacteroides thetaiotaomicron, as well as a nonpatho-
genic E. coli strain, enhances the virulence gene expression of
EHEC [9, 10]. Thus, from the perspective of the human, some
of these interactions are beneficial, whereas others are detri-
Soil habitats contain vast numbers of microorganisms and
harbor a large portion of the planet’s biological diversity .
The resident microbial community significantly affects the
fate of invading pathogens as well. Recent advances on this
topic are mainly related to the Shiga toxin producing E. coli
(STEC) such as O157:H7. For example, survival of genetical-
ly marked E. coli O157:H7 in soils is affected by soil micro-
bial community shifts, as a progressive increase of depth of
fumigation coincided with a progressively enhanced inoculant
Electronic supplementary material The online version of this article
(https://doi.org/10.1007/s00248-018-1207-z) contains supplementary
material, which is available to authorized users.
* Peng Cai
State Key Laboratory of Agricultural Microbiology, College of
Resources and Environment, Huazhong Agricultural University,
Wuhan 430070, China