Abundance, viability and culturability of Antarctic bacteria

Abstract

The viability of total number of bacteria decide the mineralisation rate in any ecosystem and ultimately the fertility of the region. This study aims at establishing the extent of viability in the standing stock of the Antarctic bacterial population I different niches besides estimating their retrievable numbers as colony forming units (CFU). It is also for the first time that retrievable anaerobic groups have been enumerated and the viability of the potential fraction capable of growing in reduced/anoxic conditions deciphered. About (0.01-1.0% of the flora have been retrieved either as aerobic or anaerobic CFUs. The total number as estimated by the AODC (Acridine Orange Director Counts0 showed that it varied from 2.62 x 10 sup(8) to 4.21 x 10 sup(10) in lakes and from 4.3 to 8.51 x 10 sup(10) 1 sup(-1) in sea water. The anaerobic retrievability in the lakes was sometimes more by 2 orders. The mean percentages of viability in different lakes varied from 4.3 to 64.5% under aerobic and from 64 to 99.3% under anaerobic conditions. The average percentage of viability in sea water was maximum at 5 m (58.5%) under aerobic conditions, and at 50 m under anaerobic conditions (78.2%). The percentage viability in the different niches suggest that the bacterial population could be active in the turnover of matter. This could particularly be tune in some of the lakes and sub-surface oceanic waters where not only the bacterial standing stock is high but also the viable forms. As growth under anaerobic conditions is generally lower, it is suggested that the propensity for higher viability and retrievability under anaerobic conditions could be a strategy for survival exhibited by the bacterial flora to overcome the double stress of low temperature and oxygen supersaturation in the Antarctic fresh waters