Bacterial diversity, physicochemical and geothermometry of South Asian hot springs

Abstract

Extreme ecosystems with enormous arrays of physicochemical or biological physiognomies serve as an important indicator of various processes occurred and/or occurring in and on the Earth. Among extreme habitats, hot springs represent geothermal features which are complex systems with a well-defined plumbing system. Besides geological tectonic based hypsography and orology annotations, the hot springs have served as hot spots for ages where there is an amalgamation of nature, religion, faith, health, and science. Thus, there remains an escalating scope to study these hot springs all over the world. The Himalayan Geothermal Belt (HGB) banquets three densely demographic countries i.e. Pakistan, India and China, that hosts numerous hot springs. Studies on the hot springs distributed over these countries reveal Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria as the predominant bacterial phyla. The bacterial diversity shows a significant positive correlation with physicochemical parameters like temperature, pH, Na⁺, HCO₃ ^-, etc. Physicochemical analyses of these hot springs indicate the water mainly as Na-Cl, Na-HCO₃, SO₄-Cl, and mixed type, with temperature ranging approximately between 100-250°C as predicted by various geothermometers. Numerous studies although done, not much of a comprehensive database of the analysis are provided on the hot springs harboured by the HGB. This review aims to give a cumulative illustration on comparative facets of various characteristic features of hot springs distributed over the HGB. These are found to be of great importance with respect to the exploitation of geothermal energy and microflora in various sectors of industries and biotechnology. They are also important sources in terms of socio-economic perspective, and routes to eco-medical tourism.

Keywords: Bacterial diversity; Himalayan geothermal belt; Hot springs; Metagenomics; Physicochemical.

Graphical abstract

Fig. 1

The spatial arrangement of Hot Springs of Himalayan Geothermal Belt, Geothermal areas of China, Central/ Peninsular India and Northern Pakistan

Fig. 2

Piper analysis: geothermal areas of China (left), geothermal areas of India and Northern Pakistan (right)

Fig. 3

Durov plot geothermal areas of India (left), geothermal areas of China and Northern Pakistan (right)

Fig. 4

Giggenbech plot, plotting geothermal areas of India, China, and Northern Pakistan.

Fig. 5

Xkms plot (left) and Xkmc plot (right) for hot springs residing in geothermal areas of India, China, and Northern Pakistan.

Fig. 6

Bubble plot representing the microbial diversity of various hot springs located in Indian, China, and Northern Pakistan

Fig. 7

Principle component analysis representing the microbial diversity and contribution of various phylum's within the hot springs of the particular country such as India (red), China (Blue) and Northern Pakistan (green)

Fig. 8

Venn diagram: a comparative analysis on the basis of bacterial diversity of four randomly categorized geothermal areas viz Indian Himalayan Geothermal Area (IHGA), Other Indian Geothermal Areas (OIGA), China Himalayan Geothermal Area (CHGA) and Northern Pakistan Geothermal Areas (NPGA).

Fig. 9

Principal Component Analysis: a correlation between various variables such as between physicochemical parameters and various phyla corresponding to various hot springs studied in this review.

Fig. 10a

Scatter analysis between Proteobacteria and various variables such as Temperature, pH, HCO₃⁻, Na⁺, etc.

Fig. 10b

Scatter analysis between Firmicutes and various variables such as Temperature, pH, HCO₃⁻, Na⁺, etc.

Fig. 10c

Scatter analysis between Cyanobacteria and various variables such as Temperature, pH, HCO₃⁻, Na⁺, etc.

Fig. 10d

Scatter analysis between Chloroflexi and various variables such as Temperature, pH, HCO₃⁻, Na⁺, etc.