ABUNDANCE AND SALT TOLERANCE OF OBLIGATELY AEROBIC, PHOTOTROPHIC BACTERIA IN A MARINE MICROBIAL MAT

Data have been collected on the abundance of obligately aerobic, bacte riochlorophyll-a-containing bacteria in a marine microbial mat on the West Frisian Island of Texel, The Netherlands. Plate counts on media r ich in organic matter revealed average numbers of 310(5).cm-3 sedimen t in the top 10 mm of the mat; the number of purple non-sulphur bacter ia was of the same magnitude. Due to the relatively small dimensions o f obligately aerobic anoxygenic phototrophic bacteria and purple non-s ulphur bacteria, compared to those of purple sulphur bacteria, the con tributions of either of the two former groups to the biomass of Bchl-a -containing organisms was approximately 3%. The specific Bchl-a-conten t of the isolated obligately aerobic phototrophs was very low (0.8 to 1.0 mug.mg-1 protein) compared to that. of purple non-sulphur bacteria (16 to 20 mug.mg-1 protein), and purple sulphur bacteria (27 to 30 mu g.mg-1). As a consequence, the relative contribution to the total Bchl a concentration of the two former groups (0.1% and 2.1%, respectively ) was negligible, compared to that of the purple sulphur bacteria (97. 8%). Salinities <50 had little effect on growth rate and yield of isol ates; at salinities between 50 and 100 the doubling time increased pro gressively with a concomitant decrease in yield; no growth occurred at salinities >140.