Alkalotolerant and Alkalophilic Bacteria in Seawater

Numerous alkalotolerant and alkalophilic bacteria, with concentrations ranging from 10 to 103 cells 100 ml-' water sample, were isolated from seawater in the Pacific and Indian Oceans using a buffered medium of pH 10.6. The pH effects on growth rates were used to define the occurrence of three types of alkalotolerant and alkalophilic bacterial groups: (1) bacteria exhibiting high growth rates throughout the pH range of 7.3 to 10.6; (2) bacteria growing well at pH 9 and below, but to a lesser extent also at pH 10.6; (3) bacteria which grow only at pH 10 to 10.6. Isolates of Type (1) are more abundant than those of the other two groups. Types (1) and (2) are tentatively named alkalotolerant; Type (3), alkalophilic. In the alkaline medium, pH fluctuation during growth was not observed, probably due to the buffer action of Na,CO, added to the medium. The alkalotolerant bacteria isolated from the Pacific Ocean consisted of Pseudornonas spp.; those isolated from Sagami Bay were Vibrio and Pseudornonas spp.; these species are common in the water area investigated. INTRODUCTION MATERIALS AND METHODS It has generally been assumed that most bacterial Water Samples species grow best in media with relatively restricted pH ranges, i, e. close to neutrality. This would be in Seawater samples were collected using a sterilized line with the situation in natural ecosystems which ORIT sampler (Taga, 1968) at the stations shown in usually feature neutral pH conditions, except in Figure 1. Seawater temperatures at different water extreme environments. However, even in normally depths were measured using protected reversing therneutral environments, wide fluctuations of pH are mometers attached to the Nansen Bottles. often observed. Rapid growth of phytoplankton, for example, can cause the environmental pH to increase temporarily to more than 10, even in seawater. Under Media such circumstances, certain bacterial populations may become subject to rapid pH fluctuations. Hitherto, the The composition of the alkaline medium for the question has remained unanswered whether or not growth of alkaline bacteria (alkalotolerant and these bacteria represent particular strains or are comalkalophilic) was as follows (g) : NaCl, 18.0; KC1, 0.6; mon members of the local ecosystem. MgC12 . 6 H20, 8.1; CaCl,, 0.8; Bacto-peptone, 1.5; While there are several reports concerning the Bacto-soytone, 1.5; Bacto-yeast extract, 1; ferric citrate, occurrence of alkaline bacteria in terrestrial soil and 0.1; agar, 15; Na2C03, 10; 1000 m1 distilled water. fresh water, this paper is the first assessment of the Na2C03 was sterilized separately and added to the distribution of alkaline bacteria in the marine environother components after cooling to 50 "C. This gave the ment. The generic composition of the bacteria isolated medium a pH of 10.6 and a Na+' concentration of and their growth versus pH fluctuations have been about 0.4 M. For media of pH 7.3, 8.0, 9.0 and 10.0, the determined. The bacteria concerned are Pseudomonas amount of Na2C03 added to the basic medium was spp. and Vibrio spp., isolated from the Pacific Ocean 0.07, 0.15, 0.42 and 2.35 g 1-l, respectively. and from Sagami Bay, Japan. The composition of the medium for heterotrophic