Publications

4467

ABSTRACT The distribution of endosymbiotic bacteria in different tissues of queens, males, and workers of the carpenter ant Camponotus floridanus was investigated by light and electron microscopy and by in situ hybridization. A large number of bacteria could be detected in bacteriocytes within the midguts of workers, young virgin queens, and males. Large amounts of bacteria were also found in the oocytes of workers and queens. In contrast, bacteria were not present in oocyte-associated cells or in the spermathecae of mature queens, although occasionally a small number of bacteria could be detected in the testis follicles of males. Interestingly, the number of bacteriocytes in mature queens was strongly reduced and the bacteriocytes contained only very few or no bacteria at all, although the endosymbionts were present in huge amounts in the ovaries of the same animals. During embryogenesis of the deposited egg, the bacteria were concentrated in a ring of endodermal tissue destined to become the midgut in later developmental stages. However, during larval development, bacteria could also be detected in other tissues although to a lesser extent. Only in the last-instar larvae were bacteria found exclusively in the midgut tissue within typical bacteriocytes. Tetracycline and rifampin efficiently cleansed C. floridanus workers of their symbionts and the bacteriocytes of these animals still remained empty several months after treatment had ceased. Despite the lack of their endosymbionts, these adult animals were able to survive without any obvious negative effect under normal cultivation conditions.

AbstractAn enteritic syndrome affecting farmed rainbow trout and occurring predominantly in summer has recently been described and related to the massive accumulation of a segmented filamentous bacterium (SFB), ‘Candidatus Arthromitus’, in the digestive tract of fish. Details of the clinical manifestations, the characteristics of the bacterium and the possible aetiology of the disease are presented in this paper. No other bacterial pathogen than ‘Candidatus Arthromitus’ was characterized in trout undergoing the enteritic syndrome. From clinical and histopathological observations, a toxin or toxic product accumulation was suspected in affected trout, and could account for the massive destruction of the intestinal mucosa. However, the origin and aetiological role of the SFB could not be clearly elucidated, although most of the filaments appeared to beviable and to produce and release strings of endospores in the lumen of the gut. The organism could not be cultured in the conditions tested, shared several morphological and structural characteristics with related bacteria described in the intestinal microflora of different vertebrate species, but no attachment structure was definitively recognized. All attempts to detect similar SFB in the fish diet orin the environment of affected fish farms were unsuccessful. It is unclear whether this organism represents a normal and not previously detected inhabitant of the intestine of trout stressed after environmental perturbation, or whether it results directly from external sources of contamination.

ABSTRACT The participation of organisms related to Rhodocyclus in full-scale enhanced biological phosphorus removal (EBPR) was investigated. By using fluorescent in situ hybridization techniques, the communities of Rhodocyclus -related organisms in two full-scale wastewater treatment plants were estimated to represent between 13 and 18% of the total bacterial population. However, the fractions of these communities that participated in polyphosphate accumulation depended on the type of treatment process evaluated. In a University of Cape Town EBPR process, the percentage of Rhodocyclus -related cells that contained polyphosphate was about 20% of the total bacterial population, but these cells represented as much as 73% of the polyphosphate-accumulating organisms (PAOs). In an aerated-anoxic EBPR process, Rhodocyclus -related PAOs were less numerous, accounting for 6% of the total bacterial population and 26% of the total PAO population. In addition, 16S ribosomal DNA sequences 99.9% similar to the sequences of Rhodocyclus -related organisms enriched in acetate-fed bench-scale EBPR reactors were recovered from both full-scale plants. These results confirmed the involvement of Rhodocyclus -related organisms in EBPR and demonstrated their importance in full-scale processes. In addition, the results revealed a significant correlation between the type of EBPR process and the PAO community.

ABSTRACT Fluorescent in situ hybridization with a 16S rRNA probe specific for Verrucomicrobia was used to (i) confirm the division-level identity of and (ii) study the behavior of the obligate intracellular verrucomicrobium “ Candidatus Xiphinematobacter” in its nematode hosts. Endosymbionts in the egg move to the pole where the gut primordium arises; hence, they populate the intestinal epithelia of juvenile worms. During the host's molt to adult female, the endosymbionts concentrate around the developing ovaries to occupy the ovarian wall. Some bacteria are enclosed in the ripening oocytes for vertical transmission. Verrucomicrobia in males stay outside the testes because the tiny spermatozoids are not suitable for transmission of cytoplasmic bacteria.