Halotolerant bacteria from saline soils in Ballesteros, Cagayan, Philippines

The coastal soils of Ballesteros, Cagayan, Philippines have gotten more saline in recent years due to anthropogenic factors like aquifer over-pumping leading to saltwater intrusion. While detrimental to agriculture in the province, this presented an opportunity to explore the possibility of bioprospecting beneficial halotolerant soil bacteria in the area that could be used for salt-tolerant crop varietal improvement. For two climactic seasons in 2019, composite soil samples (0-30 cm depth) were collected from twenty (20) sampling points, five (5) from each salinity level (Severely Saline, Moderately Saline, Slightly Saline, and Non-Saline) as determined by the 2017 BSWM Soil Salinity Map of Ballesteros, Cagayan. The soil samples were subjected to plate counts and 16S metagenomic sequencing, alongside soil textural and field pH and EC analyses. The bacterial population counts cultured in R2A-9% NaCl medium showed that the Severely Saline soil samples had counts significantly lower than the other three Salinity Levels. Meanwhile, counts in R2A-15% NaCl medium were significantly lower in Severely Saline soils collected during the wet season. Statistically higher Shannon Diversity Indices (H’) were recorded during the Dry Season. Further, the sampled soils from the non-Saline level had significantly higher H’ values compared to the sampled soils of the Moderately and Severely Saline levels, while having similar H’ values with the Slightly Saline level, resultant of much lower salt levels making it more hospitable to more bacterial species. Five potential halotolerant bacteria of interest were detected: Planococcus maritimus, Pseudomonas fluorescens, Pseudomonas azotoformans, Bellilinea caldifistulae, and Ectothiorhodospira haloalkaliphila.