HIGH RECOVERY OF CULTURABLE BACTERIA FROM THE SURFACES OF MARINE-ALGAE

The culturability of heterotrophic marine bacteria obtained from the s urfaces of two species of marine algae (Lobophora variegata and Halime da copiosa) was assessed by comparing total DAPI-stained cell counts t o colony-forming bacterial counts on two agar media. The colony-formin g bacterial counts on a low-nutrient medium (LN) consisting of seawate r and agar were significantly greater for both algal species than coun ts obtained on a high-nutrient medium (HN) similar in composition to t hat typically used for the isolation of heterotrophic marine bacteria. On average, 14 and 58%, respectively, of the total bacteria from L. v ariegata and H. copiosa were culturable on LN. These recovery rates fa r exceed those typically reported for marine bacteria. Of 119 LN strai ns obtained in pure culture, 55% failed to grow on HN. The yeast extra ct component of HN (1.5 gl(-1)) was responsible for the majority of th e observed inhibition, suggesting that this nutrient can be highly tox ic to marine bacteria. Eighty-nine percent of the strains inhibited by HN were capable of growth when the nutrients in this medium were dilu ted by a factor of 100 with seawater. Of 66 epiphytic strains, 30 (45% ) initially inhibited by HN showed the ability to adapt to this medium after a period of laboratory handling. The initial inability of low-n utrient-adapted bacteria to grow on high-nutrient media may be due to nutrient shock. The results presented here indicate that the culturabi lity of specific populations of marine bacteria can be dramatically im proved by the use of low-nutrient media. Further, the importance of de veloping new medium formulations that eliminate traditional nutrients, some of which are clearly toxic to bacteria, is demonstrated.