MICROBIOLOGICAL OBSERVATIONS IN THE ANOXIC BASIN GOLFO-DULCE, COSTA-RICA

Our basic microbiological studies of the water column and the sediment of Golfo Dulce, Costa Rica, were focused on aerobic and denitrifying sulfur-oxidizing bacteria and anaerobic sulfate-reducing bacteria. We observed no increasing numbers of total bacterial counts within the wa ter column. Although no oxygen was present hydrogen sulfide was only d etectable close to the sediment. The highest numbers of sulfate-reduci ng bacteria measured by Most-Probable-Number counts were found in or c lose to the sediment. In the anoxic bottom water sulfide-oxidizing bac teria typically containing large sulfur globules were observed microsc opically. They were identified as free-swimming Thiovulum and Thiospir a species. At one station large vacuolated forms of the filamentous co lourless sulfur bacterium Beggiatoa were noted. Together with these su lfur containing bacteria there were long free swimming rods showing no sulfur inclusions of unknown character. The microscopic observations showed good correlation with Most-Probable Number-counts and molecular biological techniques for sulfate-reducing bacteria.