Culture-Dependent Study of Microbial Diversity of Lake Chaka

Jiang and colleagues described the microbial diversity of Lake Chaka, a hypersaline lake in China (2). Numerous typographical errors occur in the names of taxa (e.g., “Salinibacter rubber,” “Holomonas,” “Euryarchaeaota,” “Haloanaerobium lacurosei,” and “Halosimplex carlsbadensis”). The “culture-dependent” methods used to assess microbial diversity were inadequate, as only liquid enrichment cultures were used, which would be expected to recover highly biased, relatively homogeneous populations. Direct plating with extended incubation periods has been shown to recover significant fractions of the dominant microbial groups in soil (4) and in salt water (1). Indeed, the success of such methods in cultivating salt lake microbes is eminently demonstrated by the Maras salterns study (3) that was published in the very same issue as that of Jiang et al. The Lake Chaka study gives no estimate of the ratio of haloarchaea to bacteria in the water column, but it is likely that a large proportion of the >10⁶ cells/ml are haloarchaea. However, only three such isolates are described, a number that is insufficient to assess the microbial diversity of the lake and speaks of serious problems with the culture-dependent aspect of the study. The salt concentration in the lake water is stated as 32.5% (i.e., 32.5 g/100 ml), yet ion concentrations given in the lake water chemistry section (Results) add up to about 3%. Even more confusing is that many ions are stated to have two levels, e.g., 4 and 957 mg/liter for K⁺. Presumably, these are more typographical errors but in this type of study it is important to present the water chemistry correctly. The soluble salt concentration in the water-sediment interface sample (Fig. 2B, 0 cm) was also surprisingly low (∼3%) given that it is in direct contact with the 32.5% salt lake water and the sediment itself is stated to be rich in halite (solid salt).