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S.E. Potter, unpublished data). Dense bioÝlms were found within the midgut of these Þies, with less
complex but prevalent bioÝlms elsewhere in the alimentary tract. BioÝlms were also found in all life
stages of
R. completa
(Potter, 2001) and
C. capitata
(Lauzon et al., 2002).
BioÝlms form within the adult tephritid within the Ýrst few hours post eclosion. We found that
upon emergence,
C. capitata
,
A. ludens
,
R. pomonella
, and
R. completa
Þies lack a peritrophic
membrane and, thus exposed, lush carpets of microvilli extend into the lumen and with very few
bacteria present. A peritrophic membrane, or matrix, forms within hours, and subsequently bacterial
numbers increase. Initially, the bacteria can be seen studded primarily along the perimeter of the
peritrophic membrane. Bacterial numbers continue to increase, and microcolonies and subsequently
late-stage bioÝlms form. A complete bioÝlm is formed typically within a tephritid gut 12 to 18 h
post eclosion. Planktonic bacteria, either ingested as natural food or from the outer layers of gut
microcolonies, likely arrive at and leave these bioÝlms routinely.
To further characterize bioÝlm formation within the fruit Þy gut, we used strains of
E. agglo-
merans
and
K. pneumoniae
that were transformed to express different colored Þuorescent proteins
(Peloquin et al., 2000, 2002) and monitored their establishment within the
R. completa
and
C.
capitata
gut. Newly emerged Þies fed on diet containing the bacteria, and we subsequently examined
their alimentary canal and reproductive organs for the presence and arrangement of the bacterial
species. We paid particularly close attention to the density and channels that deÝned the bioÝlm
structures. To reiterate, the structure of a bioÝlm can lend important insight to the functions that
occur within a bioÝlm. Though biochemical events are often the deÝning parameters of a bioÝlm,
we cannot overlook the fact that physically these bioÝlms prevent nonindigenous or threatening
microbial species from becoming established in the tephritid alimentary canal organs and provide
a physical barrier to toxic or noxious compounds. BioÝlms likely direct ingested materials that are
not digested efÝciently through the alimentary canal.
We found that
Enterobacter
and
Klebsiella
spp. colonized rapidly within the alimentary canals
of both fruit Þy species. Similarly, the different bacterial strains routinely colocalized, notably in
areas bordering channels and pores that coursed throughout and meandered within the bioÝlms.
There were areas within the bioÝlm where the two species did not colocalize, but typically the
colocalized bacteria were present at the borders of the channels and pores. Indeed, this suggests
that colocalization relates to the joint participation of
Enterobacter
and
Klebsiella
spp. in nitrogen
cycling. Nitrogenous uric acid enters the midgut and
Enterobacter
spp. that produce enzymes, such
as uricase, that catabolize the uric acid to urea.
Klebsiella
spp. typically produce urease that
catabolizes the urea to ammonia or ammonium products that are assimilated across the Þy epithe-
lium and used in anabolic processes for the Þy (Lauzon et al., 2000). Urease activity does occur
within the midgut of
C. capitata
and
R. completa
, and this enzymatic action resulted in the
production of ammonia or ammonium products produced by bacteria-degrading protein including
uric acid (Lauzon and Potter, 1999).
Catabolic processes are unlikely to be the exclusive biochemical activities that occur with the
gut bioÝlms. We have found that bioÝlms also exist in the crops of
C
.
capitata
, although their
structure is not as extensive as those seen in the midgut of the Þies. Though the crop is considered
to be a holding chamber for ingested materials, Lu and Teal (2001) found that mating pheromone
components were produced within the crop of
A. suspensa
, the Caribbean fruit Þy. It is possible
that bacteria within the crop may contribute to the synthesis of these compounds.
Enterobacter
and
Klebsiella
spp. have been isolated from the Caribbean fruit Þy (C.R. Lauzon and N.D. Epsky, 1990,
unpublished results). Epsky et al. (1998) found that
A. suspensa
were attracted to odors produced
by
E. agglomerans
. It is likely that different bioÝlms in different areas of the alimentary tract of
fruit Þies are engaged in a variety of metabolic activities.
While examining the gut using our transformants we found that the bacteria also migrated to
the ovaries and formed bioÝlms on the egg surface. Moreover, the transformants were detected in
all life stages of
C. capitata
through two successive generations (C.R. Lauzon et al., 2002, unpub-
lished results). The vertical transmission of these two bacterial species fortiÝes our hypothesis that
