Microbial Flora Associated with the Digestive System ofUpogebia Stellata(Crustacea: Decapoda: Thalassinidea)

The digestive system of the thalassinidean mud-shrimpUpogebia stellatawas investigated using scanning electron microscopy (SEM). Within the lumen of the midgut both filamentous and rod-shaped bacteria were observed. The hindgut microbial populations were dominated by dense mats of epimural rod-shaped bacteria. The gut contents were often dominated by diatoms but also contained bacteria, dinoflagellates, plant and algal fragments. Direct bacterial counts by epifluorescence microscopy along the length of the gut revealed a slight decrease in numbers within the midgut moving from the anterior to the posterior regions, and then a dramatic rise in numbers within the hindgut. Numbers decreased again in the posterior regions of the hindgut. Common in the transient / resident samples (bacterial population when gut contents were present) were enterobacteria and an unidentified fermenter conforming to an isolate named X-ferm. However, nearly 30% of the bacterial isolates remained unidentified. The resident-only bacterial isolates from the gut (determined when the gut was empty) were dominated by the X-ferm bacteria and to a lesser extent by the generaVibrioandAeromonas. With respect to the enzyme capabilities of the gut bacteria, the resident-only collection of bacterial isolates showed much higher levels of amylase, cellulase, chitinase, protease and lipase activity than the transient/resident bacterial isolate collections, suggesting that the indigenous bacteria are likely to play a significant role in the digestion of the gut contents. Thalassinidean shrimps are likely to play an important role in the breakdown of plant and detrital material, and the recycling of nutrients in marine benthic systems.