The potential of Pseudomonas sp. as a phosphate solubilizer for phytoplankton in Penaeus vannamei rearing

Abstract

Phosphorus is an essential element in aquaculture waters, significantly influencing phytoplankton growth. However, phosphorus is often present in a limited organic form and is rarely found as free dissolved inorganic phosphorus (orthophosphate). The application of Pseudomonas AHN.4 offers an alternative approach to enhancing orthophosphate availability for phytoplankton in aquaculture systems through its phosphate-solubilizing capability. This study aimed to evaluate the potential of Pseudomonas AHN.4 as a phosphate-solubilizing bacterium and its effect on phytoplankton profile in the P. vannamei culture system. The Pseudomonas sp. isolate, sourced from the mangrove waters of BLUPP (Balai Layanan Usaha Produksi Perikanan) Karawang, demonstrated phosphate-solubilizing ability by producing a clear zone on Pikovskaya agar with a solubilization index of 2.4 mm. Molecular tests revealed a close genetic relationship to Pseudomonas oryzihabitans. Hemolytic assay showed non-pathogenic properties. The bacteria were applied to P. vannamei rearing media with three treatments and one control, using bacterial densities of 10¹, 10³, and 10⁵ CFU/mL, each replicated three times. The bacterial application significantly affected phytoplankton growth compared to the control (0 CFU/mL). The highest phytoplankton abundance was recorded in treatment 10⁵ CFU/mL, with 173,333 ± 10,006 cell/mL, a diversity index of 1.20, a uniformity index of 0.67, and dominance of 0.43. The increased phytoplankton supported an absolute growth of P. vannamei by 1.86 ± 0.02 g with the best survival rate of 86.67%. Although statistically not significantly different between treatments (P>0.05), these results suggest that treatment 10⁵ has relevant application potential and is more effective at providing orthophosphate to phytoplankton.

Keywords: aquaculture, orthophosphate availability, phytoplankton, Pseudomonas sp., P. vannamei