To decrease the polyhydroxyalkanoate (PHA) production cost by supplying renewable carbon sources has been an important aspect in terms of commercializing this biodegradable polymer. The production of biodegradable poly (3-hydroxyalkanoates) (PHA) from raw potato starch by the Bacillus cereus 64-INS strain (GenBank Accession no. JQ013099) isolated from domestic sludge has been studied in a lab-scale fermenter. The bacterium was screened for the degradation of raw potato starch by a starch hydrolysis method and for PHA production by Nile blue A and Sudan black B staining. Shake-flask cultures of the bacterium with glucose [2% (wv1)] or raw potato starch [2% (wv-1)] produced PHA of 64.3 5% and 34.68 % of dry cell weight (DCW), respectively. PHA production was also carried out in a 5-L fermenter under control conditions that produced 2.78 gl-1 of PHA and PHA content of 60.53 % after 21 hours of fermentation using potato starch as the sole carbon source. Gas chromatography–mass spectroscopy (GC-MS) analyses confirmed that the extracted PHA contained poly(3hydroxybutyrate) (PHB) as its major constituent (>99.99 %) irrespective of the carbon source used. The article describes, for what we believe to be the first time, PHB production being carried out without any enzymatic or chemical treatment of potato starch at higher levels by fermentation. More work is required to optimize the PHB yield with respect to starch feeding strategies. An efficient PHA producing bacterial strain Bacillus sp. AZR-1 (GenBank Accession no. JQ398616) was isolated and characterized morphologically and biochemically. The strain was identified as Bacillus sp. AZR-1 on the genetic basis of 16S rRNA gene sequence. Bacillus sp. AZR-1 produced 40% PHA contents when grown on N-limited mineral salt medium supplemented with glucose in shake flasks. Starch and sodium gluconate were found to be other putative carbon sources for PHA production as the bacterium produced 22 and 17% PHA on these sources. FTIR confirmed the presence of SCL-PHA monomers in the polymer extracted from the bacterium. The PHA synthase gene (phaC) was partially amplified and sequenced which showed maximum similarity with the PHA synthase of Bacillus weihenstephanensis KBAB4. Two potential PHA producing strains identified as Pseudomonas aeruginosa strain IFSand (GenBank Accession no. JQ041638) P. aeruginosa strain 30N (GenBank Accession no. JQ041639) based on 16S rRNA gene sequence identity were cultivated under nitrogen limited xvi conditions to study their PHA biosynthesis capabilities. The strain IFS and strain 30N produced 1.36 gl-1 and 1.40 gl-1 dry biomass with percentage PHA contents of 44.85 % and 45.74 % respectively when grown on glucose as carbon source. The PHA was identified as Poly(3hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) by Fourier transform infra-red spectroscopy (FTIR) and gas chromatography coupled with mass spectrometry (GC-MS). The PHA synthase genes of these strains was isolated, sequenced and were analyzed using bioinformatic tools that showed they belonging to type 2 PHA synthases and presented their evolutionary relationships with PHA synthases of other Pseudomonas species. The experimental results of this study highlight the importance of these strains for future use of bacterial biopolymer production growing on simple and in-expensive carbon sugars. PHAs are synthesized by many bacterial species under some unfavorable conditions, such as the limitation of any essential nutrient present in the growth medium. These limitations may refer to the very low amounts of either carbon, phosphorous, nitrogen, potassium or oxygen etc. But it was very unusual to see no PHA production at all by the isolated bacterial strains Pseudomonas sp. P65 (GenBank Accession no. KF573429) and Pseudomonas sp. F15 (GenBank Accession no. KF573430) under P-limited conditions and PHA production was only observed under nitrogen limitations. Although the strain P65 and strain F15 were found to produce PHA on various carbon sources yet they preferred the simple monomers like glucose, fructose and lactose for relatively higher cellular growth and PHA production. It seems that our strains follow the de novo biosynthetic pathway for the production of PHA using acetyl-coA produced from glucose as the precursor molecule. It was observed that the N-limited medium supported the growth of Pseudomonas sp. F15 to1.46 gl-1and 1.20 gl-1of dry cell weight (DCW) after 24 h and 48 h of incubation respectively. The PHA produced in terms of percentage content of DCW went down from 52.85 % to 22.59 % respectively during the above incubation period. In case of Pseudomonas sp. P65, N-limited medium proved to be ideal for the PHA accumulation of 55.56 % and 23.73 % after 24 h and 48 h. The dry cell biomass accounted to be 1.56 gl-1 and 1.23 gl-1 for the said period. Overall, the PHA production and DCW formation from fructose, lactose, sucrose and molasses by these strains were found to be lower to that of glucose supplemented media. Moreover, there was a general trend of decrease in cellular growth as well as PHA accumulation from 24 h of incubation towards the 48 h of incubation by these bacteria on these carbon sources. Gluconic acid, the oxidized form of glucose proved to be the best carboxylic acid as compared to heptanoic acid, xvii sodium salt of octanoic acid, nonanoic acid and decanoic acid, for the PHA production and DCW formation by these two strains. In fact, a higher DCW value of about 1.61 gl-1 was accounted for strain F15 with ~34 % PHA contents. In comparison the strain P65 grew up to the 1.34 gl-1 DCW and with PHA contents of 30.85 %. PHA yield from gluconic acid was nevertheless lower only to glucose for both strains. It was observed that high concentrations of nitrogen favoured the bacterial growth of both strains. C:N molar ratio of 1:1 resulted in highest DCW values of 2.82 gl-1 and 2.16 gl-1 for strain P65 and strain F15 respectively. Increase in the C:N molar values by reducing the nitrogen contents in the medium showed prominent negative effect on the growth of both strains. The PHA contents on the other hand went in sharp increase when the amount of nitrogen source was decreased gradually in the media. Accumulation of only MCL-PHA was observed for both Pseudomonas sp. P65 and Pseudomonas sp. F15 on glucose as sole carbon source at all the C:N molar ratios. Overall, the 3-hydroxyoctanoate (3-HO), 3-hydroxydecanoate (3-HD), 3hydroxydodecanoate (3-HDD), and 3-hydroxytetradecanoate (3-HTD) monomers were found to be prominent components while little amounts of 3-hydroxyhexanoate (3-HHx), 2hydroxydecenoate (2-HDE), methyl, 3-methoxytetradecanoate (3-MeTD) and tetradecanedioic, 3,6-epoxy, dimethyl ester (3,6-EDA) were also found. Pseudomonas sp. F15 and Pseudomonas sp. P65 accumulated some unusual monomers like 3-MeTD and C14 EDA as well. Production of medium-chain-length poly-3-hydroxyalkanoates (MCL-PHAs) was optimized by Pseudomonas sp. P65. A predetermined growth rate was selected for fed-batch feeding of glucose to get a high cell density bacterial culture in a 5 L Minifors bioreactor. Polymer was extracted from the bacteria and purified for characterization by GC-FID or GC-MS. MCLPHAs were produced from unrelated carbon source i.e. glucose, instead of the short chain length SCL-PHA, that is characteristic when glucose is used as the carbon source. Gas chromatographyFID and GC-MS confirmed the presence of MCL-PHAs i.e. 3-hydroxyoctanoate (3-HD), 3hydroxydecanoate (3-HD) and 3-hydroxydodecanoate (3-HDD) monomers. A modified Fed-batch fermentation strategy produced bacterial density of 15.23 gl-1 with PHA contents of 58.68 % of DCW. The isolated bacteria have shown great interest in their biopolymer production at higher levels using unrelated carbon source, glucose. The limitation of phosphate or nitrogen to produce unfavorable conditions has been addressed in this work as well.