E. coli competence- Fish bacteria
chris at esb.ucp.pt
Fri Sep 23 09:40:04 EST 1994
I too am intersted in the communication, antagonism and
competitive balances of bacteria. My particular research is on fresh fish
spoilage (try saying that after eating a biscuit!). As has already been
mentioned in this series of messages, many Gram -ve bacteria are believed
to communicate (re. N-acyl homoserine lactones (Review, Swift et al.
Trends in Microbiol 2(6) 193-198)), information concerning cell densities,
energy, maturity, micronutrients and oxygen availability. For my
particular work micronutrients, especially ferric iron, are of interest.
The production of siderophores by fish bacteria (mostly Pseudomonadacae)
are interestingly controlled and are linked to other environmental
virulence factors (antibiotics and other toxins).
Fresh fish spoilage is quite rapid (about 15d at 4'C - depends upon
fish species) and mediated by the growth of bacteria, but it is fair to
say that most of the bacteria growing on fish do not produce significant
spoilage characteristics. Those bacteria that do spoil the fish are
generally in a significant minority, however if the balance of the
non-spoilling micro-organisms is upset spoilage may become more rapid.
This suggests that the spoilage organisms may be inhibitted to some
extent by the 'non-spoilage' competitors.
There are more mechanisms at work than just iron limitation, some
bacteria are able to enhance each-others growth (mechanism under
investigation- possibly homoserine lactones) on fish agar, others protect
eachother from the inhibition of a third (siderophore cross-feeding?).
There is a huge field waiting to be investigated further. The
implications of some of the results may also be felt by the
mathematicians who believe they can model mixed bacterial growth in complex
matrices such as foods...Ha! Believe it when I see it.
Is there anyone else who is tring to sort out mixed culture
growth? It is far more complicated than I thought it could ever be, fish
are a nightmare as the taxonomy of most of the marine bacteria is dubious
and the primary inoculum is very diverse. Remember lactic acid bacteria
are not the only ones to produce antimicrobials.
This is my first message to a list, and like most virgins I'm a little
nervous of the outcome. Appologies for being so verbose.
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