COMPARISON OF POLYHYDROXYALKANOATES BIOSYNTHESIS, MOBILIZATION AND THE EFFECTS ON CELLULAR MORPHOLOGY IN SPIRULINA PLATENSIS AND SYNECHOCYSTIS SP. UNIWGE

Abstract

Filamentous Spirulina platensis and unicellular Synechocystis sp. UNIWG showed capability of synthesizing poly(3-hydroxybutyrate) [P(3HB)] under nitrogen starvation conditions with a maximum accumulation of up to 10 and 14 wt% of the cell dry weight (CDW), respectively under mixotrophic culture conditions. Intracellular degradation (mobilization) of P(3HB) granules by both strains was initiated by the restoration of a nitrogen source. The mobilization of P(3HB) was faster in S. platensis (80% degradation in a period of 8 days) than in Synechocystis sp. (57% degradation in a period of 10 days). Transmission electron microscopy (TEM) revealed that the mobilization of P(3HB) involved changes in granule quantity and morphology. P(3HB) granules became irregular in shape and the boundary region was less defined. Ultrastructural analysis also revealed that Synechocystis sp. UNIWG cells from the growth phase was covered with pilus-like structures. However, these pilus-like structures were not observed in cells from the polyhydroxyalkanoate (PHA) accumulation phase. It is suggested that these pilus-like structures may play an important role for the survival of this cyanobacterium under stress conditions.

Spirulina platensis filamentus dan Synechocystis sp. UNIWG uniselular menunjukkan kebolehan mensintesis poli(3-hidroksibutirat) [P(3HB)] di bawah keadaan bebas nitrogen dengan akumulasi maksimum hingga 10% dan 14% P(3HB) masing-masing daripada berat kering sel (CDW) di bawah keadaan kultur miksotrofik. Pendegradan intraselular (mobilisasi) granul P(3HB) oleh kedua-dua strain dimulakan dengan pembekalan semula sumber nitrogen. Mobilisasi P(3HB) dalam S. platensis adalah lebih cepat (80% telah didegradasikan dalam masa 8 hari) berbanding Synechocystis sp. (57% telah didegradasikan dalam masa 10 hari). Mikroskop elektron transmisi (TEM) menunjukkan mobilisasi P(3HB) melibatkan perubahan dalam kuantiti dan morfologi granul P(3HB). Bentuk granul P(3HB) berubah menjadi tidak sekata dan sempadannya tidak jelas kelihatan. Analisis ultrastruktur juga menunjukkan sel Synechocystis sp. UNIWG daripada fasa pertumbuhan diselaputi oleh struktur seperti pilus. Walau bagaimanapun, struktur seperti pilus ini tidak kelihatan pada sel semasa fasa akumulasi polihidroksialkanoat (PHA). Adalah dicadangkan bahawa struktur seperti pilus mungkin memainkan peranan yang penting dalam kemandirian sianobakteria ini di bawah keadaan stres.