An isolated, synthetic, or recombinant nucleic acid comprising: a sequence encoding a polypeptide having an alpha amylase activity optimum at pH 7 or less, wherein said sequence has at least 95%, 96%, 97%, 98%, 99% or 100% sequence identity to the sequence of SEQ ID NO: 127, or a sequence encoding a polypeptide having an alpha amylase activity optimum at pH 7 or less, wherein the amino acid sequence of the polypeptide has at least 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 128, or an enzymatically active fragment thereof, wherein the fragment has an alpha amylase activity optimum at pH 7 or less, or a sequence encoding a polypeptide having alpha amylase activity, wherein the amino acid sequence of the polypeptide has at least 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO:128, or an enzymatically active fragment thereof, or a sequence encoding a polypeptide having alpha amylase activity, wherein the polypeptide's amino acid sequence is the sequence of SEQ ID NO: 128, or enzymatically active fragments thereof, wherein the fragment has an alpha amylase activity optimum at pH 7 or less, the sequence of any of,,, or encoding a polypeptide lacking a signal sequence, (i) a sequence of any of,,, or encoding a polypeptide further comprising a heterologous nucleic acid sequence; (ii) the sequence of (i), wherein the heterologous nucleic acid sequence encodes a signal sequence; (iii) the sequence of (ii), wherein the heterologous signal sequence comprises an amylase signal sequence, or a nucleic acid sequence completely complementary to any nucleic acid sequence of to. a sequence encoding a polypeptide having an alpha amylase activity optimum at pH 7 or less, wherein said sequence has at least 95%, 96%, 97%, 98%, 99% or 100% sequence identity to the sequence of SEQ ID NO: 127, or a sequence encoding a polypeptide having an alpha amylase activity optimum at pH 7 or less, wherein the amino acid sequence of the polypeptide has at least 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 128, or an enzymatically active fragment thereof, wherein the fragment has an alpha amylase activity optimum at pH 7 or less, or a sequence encoding a polypeptide having alpha amylase activity, wherein the amino acid sequence of the polypeptide has at least 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO:128, or an enzymatically active fragment thereof, or a sequence encoding a polypeptide having alpha amylase activity, wherein the polypeptide's amino acid sequence is the sequence of SEQ ID NO: 128, or enzymatically active fragments thereof, wherein the fragment has an alpha amylase activity optimum at pH 7 or less, the sequence of any of,,, or encoding a polypeptide lacking a signal sequence, (i) a sequence of any of,,, or encoding a polypeptide further comprising a heterologous nucleic acid sequence; (ii) the sequence of (i), wherein the heterologous nucleic acid sequence encodes a signal sequence; (iii) the sequence of (ii), wherein the heterologous signal sequence comprises an amylase signal sequence, or (i) a sequence of any of,,, or encoding a polypeptide further comprising a heterologous nucleic acid sequence; (ii) the sequence of (i), wherein the heterologous nucleic acid sequence encodes a signal sequence; (iii) the sequence of (ii), wherein the heterologous signal sequence comprises an amylase signal sequence, or a nucleic acid sequence completely complementary to any nucleic acid sequence of to.