Cultivation-Dependant Assessment, Diversity, and Ecology of Haloalkaliphilic Bacteria in Arid Saline Systems of Southern Tunisia

Abdellatif Boudabous,Amel Guesmi,Ameur Cherif,Afef Najjari,Hanen Cherif,Darine El Hidri,Besma Ettoumi,Chadlia Hamdi

doi:10.1155/2013/648141

Abdellatif Boudabous, Amel Guesmi + Show 6 more

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https://doi.org/10.1155/2013/648141

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Abstract

Haloalkaliphiles are polyextremophiles adapted to grow at high salt concentrations and alkaline pH values. In this work, we isolated 122 haloalkaliphilic bacteria upon enrichments of 23 samples from 5 distinct saline systems of southern Tunisia, growing optimally in media with 10% salt and at pH 10. The collection was classified into 44 groups based on the amplification of the 16S–23S rRNA internal transcribed spacers (ITS-PCR). Phylogenetic analysis and sequencing of the 16S rRNA genes allowed the identification of 13 genera and 20 distinct species. Three gram-positive isolates showing between 95 and 96% of 16S rRNA sequence homology with Bacillus saliphilus could represent new species or genus. Beside the difference in bacterial diversity between the studied sites, several species ecological niches correlations were demonstrated such as Oceanobacillus in salt crust, Nesterenkonia in sand, and Salinicoccus in the rhizosphere of the desert plant Salicornia. The collection was further evaluated for the production of extracellular enzymes. Activity tests showed that gram-positive bacteria were mostly active, particularly for protease, lipase, DNase, and amylase production. Our overall results demonstrate the huge phenotypic and phylogenetic diversity of haloalkaliphiles in saline systems of southern Tunisia which represent a valuable source of new lineages and metabolites.

Highlights

Extreme environments are distributed on Earth which were thought to prevent the existence of life
Enrichment was performed on Soap lake Basal Medium (SLBM) [25], an enrichment medium for moderately haloalkaliphilic bacteria, containing (L−1): CaSO4 4 mg; FeSO4 1 mg; NaCl 10 g; SiO2 5 mg; MgCl2 4 mg; MnSO4 4 mg; NH4O3 50 mg; Na2SO4 13 g; KH2PO4 3 g; K2HPO4 3 g; Na2CO3 1 g, and 1 mL trace element stock solution consisting of (L−1) sodium nitriloacetate 1.5 g; MgSO4⋅7H2O 3 g; MnSO4⋅7H2O 0.5 g; NaCl 1 g; FeSO4⋅7H2O 0.1 g; CaCl2⋅2H2O 0.1 g; CoCl2⋅6H2O 0.1 g; ZnCl2 0.13 g; CuSO4⋅5H2O 0.01 g; AlK (SO4)2⋅12H2O 0.01 g; H3BO3 0.01 g; Na2MoO4⋅2H2O 0.025 g; NiCl2⋅6H2O 0.024 g, and Na2WO4⋅2H2O 0.025 g
The diversity of cultivable haloalkaliphilic bacteria was evaluated using culture enrichment followed by isolation on haloalkaliphile medium

Summary

Introduction

Extreme environments are distributed on Earth which were thought to prevent the existence of life. These habitats are characterized by extreme conditions including physical (temperature and pressure) and chemical parameters (salinity and pH) [1]. In 1982, the term haloalkaliphile was used for the first time to describe bacteria that are both halophilic and alkaliphilic [2]. This group of bacteria is able to grow optimally or very well at pH values at or above 10 along with high salinity (up to 25% (w/v) NaCl) [3]

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